Neurology_Adams

Neurology_Adams. Hysterical, or psychogenic blindness, is described in Chap. 47, along with other features of hysteria, but a few comments are in order here. Feigned or hysterical visual loss is usually detected by attending to the patient’s activities when he thinks he is unobserved, and it can be confirmed by a number of simple tests. Complete feigned blindness is disproved by observing the normal ocular jerk movements in response to a rotating optokinetic drum or strip, or by noting that the patient’s eyes follow their own image in a mirror that is moved in front of them. The hysterical nature of total monocular blindness is apparent from the presence of a normal direct pupillary response to light. An optokinetic response in the nonseeing eye (with the good eye covered) is an even more convincing test. The visual evoked potential from the allegedly blind eye is also normal. Hysterical monocular loss may also be revealed by the use of red-green glasses and an acuity chart with red and green letters,


Neurology_Adams

Neurology_Adams. The visual evoked potential from the allegedly blind eye is also normal. Hysterical monocular loss may also be revealed by the use of red-green glasses and an acuity chart with red and green letters, where each eye can only see letters with the color of its lens. The patient cannot tell which letters should be visible to them, and the intact acuity in the involved eye is soon exposed. Hysterical homonymous hemianopia is rare and is displayed mostly by practiced malingerers; all manner of field defects are common in this population (Keane). The uniformly constricted tubular field defect of hysteria, which does not expand as the testing distance is increased, has already been mentioned. Starand spiral-shaped visual fields results obtained by manual kinetic (Goldmann) perimetry are also indicative of psychogenic visual loss.


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Neurology_Adams. Cerebral Forms of Blindness and Visual Agnosia (See Also Chap. 21) The ability to recognize visually presented objects and words depends on the integrity not only of the visual pathways and primary visual area of the cerebral cortex (area 17 of Brodmann) but also of those cortical areas that lie just anterior to area 17 (areas 18 and 19 of the occipital lobe and area 39—the angular gyrus of the dominant hemisphere). Blindness that is the result of destruction of both visual and adjacent regions of the occipital lobes is termed cortical or cerebral blindness. Another remarkable condition exists in which the patient denies or is oblivious to blindness despite overt manifestations of the defect (Anton syndrome).


Neurology_Adams

Neurology_Adams. In distinction to these forms of blindness, there is a less-common category of visual impairment in which the patient cannot understand the meaning of what he sees, that is, visual agnosia. Primary visual perception is more or less intact, and the patient may accurately describe the shape, color, and size of objects and draw copies of them. Despite this, he cannot identify the objects unless he hears, smells, tastes, or palpates them. The failure of visual recognition of words alone is called pure word blindness, or alexia. Visual-object agnosia rarely occurs as an isolated finding: as a rule, it is combined with alexia, homonymous hemianopia, or both. These abnormalities arise from lesions of the dominant occipital cortex and adjacent temporal and parietal cortex (angular gyrus) or from a lesion of the left calcarine cortex combined with one that interrupts the fibers crossing from the right occipital lobe (see Fig. 21-6). In the latter case, fibers responsible for writing are


Neurology_Adams

Neurology_Adams. from a lesion of the left calcarine cortex combined with one that interrupts the fibers crossing from the right occipital lobe (see Fig. 21-6). In the latter case, fibers responsible for writing are spared, and the patient remains with a syndrome of alexia without agraphia.


Neurology_Adams

Neurology_Adams. Failure to understand the meaning of an entire picture even though some of its parts are recognized is referred to as simultanagnosia, and is found in bilateral lesions of the occipital–parietal junction. When combined with deficits in visual control of hand and eye movements (optic ataxia and ocular apraxia), the resulting condition is referred to as Balint syndrome. A failure to recognize familiar faces is called prosopagnosia and typically results from occipital–temporal lesions. These and other variants of visual agnosia (including visual neglect) and their pathologic bases are dealt with more fully in Chap. 21.


Neurology_Adams

Neurology_Adams. Other cerebral disturbances of vision include various types of distortion in which images seem to recede into the distance (teleopsia), appear too small (micropsia), or, less frequently, seem too large (macropsia). If such distortions are perceived with only one eye, a retinal lesion should be suspected. If perceived with both eyes, they usually signify disease of the temporal lobes, in which case the visual disturbances tend to occur in attacks and are accompanied by other manifestations of temporal lobe seizures (see Chap. 15). Palinopsia, a persistence of repetitive afterimages, similar to the appearance of a celluloid movie strip, occurs with right parietooccipital lesions; it has been a consequence of seizures in the cases we have encountered, but instances associated with static disorders (tumor, infarction) have been described as well. Patients describe the images as “trailing” or “echoing.” With parietal lobe lesions, objects may appear to be askew or even turned upside down.


Neurology_Adams

Neurology_Adams. (tumor, infarction) have been described as well. Patients describe the images as “trailing” or “echoing.” With parietal lobe lesions, objects may appear to be askew or even turned upside down. More often, lesions of the vestibular nucleus or its immediate connections produce the illusion that objects are tilted or turned upside down (tortopsia), or that straight lines are curved. Presumably this is the result of a mismatch between the visual image and the otolithic, vestibular input to the visual system.


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Neurology_Adams. Abnormalities of Color Vision Normal color vision depends on the integrity of cone cells, which are most numerous in the macular region. When activated, they convey information to special columns of cells in the striate cortex. Three different cone pigments with optimal sensitivities to short (blue), middle (green), and long (orange-yellow) wavelengths are said to characterize these cells. Transmission to higher centers for the perception of color is effected by neurons and axons that encode at least two pairs of complementary colors: red-green in one system and yellow-blue in the other. In the optic nerves and tracts, the fibers for color are of small caliber and seem to be preferentially sensitive to certain noxious agents and to pressure; thus, dyschromatopsia is a common feature of many optic neuropathies. The visual fields for blue-yellow are smaller than those for white light, and the red and green fields are smaller than those for blue-yellow.


Neurology_Adams

Neurology_Adams. Diseases may affect color vision by abolishing it completely (achromatopsia) or partially by quantitatively reducing one or more of the three attributes of color—brightness, hue, and saturation. Alternatively, only one of the complementary pairs of colors may be lost or reduced, usually the red-green axis. The disorder may be congenital and hereditary or acquired. The most common form, and the one to which the term color blindness is usually applied, is a male sex-linked inability to see red and green while normal visual acuity is retained. The main problem arises in relation to traffic lights, but patients learn to use the position of the light as a guide. Several other genetic abnormalities of cone pigments and their phototransduction have been identified as causes of achromatopsia. The defect cannot be seen by inspecting the retina. A failure of the cones to develop or a degeneration of cones may cause a loss of color vision, but in these conditions visual acuity is often


Neurology_Adams

Neurology_Adams. The defect cannot be seen by inspecting the retina. A failure of the cones to develop or a degeneration of cones may cause a loss of color vision, but in these conditions visual acuity is often diminished, a central scotoma may be present, and, although the macula also appears to be normal ophthalmoscopically, fluorescein angiography shows the pigment epithelium to be defective. Whereas congenital color vision defects are usually protan (red) or detan (green), leaving yellow-blue color vision intact, most acquired lesions affect all colors, at times disparately. Lesions of the optic nerves usually affect red-green more than blue-yellow; the opposite is true of retinal lesions. An exception is a rare, dominantly inherited, optic atrophy, in which the scotoma mapped by a large blue target is larger than that for red.


Neurology_Adams

Neurology_Adams. Damasio has drawn attention to a group of acquired deficits of color perception with preservation of form vision, the result of focal damage (usually infarction) of the visual association cortex, and subjacent white matter. Color vision may be lost in a quadrant, half of the visual field, or the entire field. The latter, or full-field achromatopsia, is the result of bilateral occipitotemporal lesions involving the fusiform and lingual gyri, a localization that accounts for its frequent association with visual agnosia (especially prosopagnosia), and some degree of visual field defect. A lesion restricted to the inferior part of the one occipitotemporal lobe, sparing both the optic radiations and striate cortex, may cause a contralateral hemiachromatopsia. With a left-sided lesion in this location, alexia may be associated with the right hemiachromatopsia.


Neurology_Adams

Neurology_Adams. In addition to the losses of perception of form, movement, and color, lesions of the visual system may also give rise to a variety of positive sensory visual experiences. The simplest of these are called phosphenes, that is, flashes of light and colored spots in the absence of luminous stimuli. Mechanical pressure on the normal eyeball may induce them at the retinal level, as every child discovers. Or they may occur with disease of the visual system at many different sites. As mentioned earlier, elderly patients commonly complain of flashes of light in the peripheral field of one eye, most evident in the dark (Moore lightning streaks); these are related to vitreous tags that rest on the retinal equator, and may be quite benign, or may be residual evidence of retinal detachment. Autoimmune and cancer associated retinopathy is frequently associated with photopsias prior to visual loss. Retinal toxicity from digitalis causes chromatopsia with a characteristic “yellowish vision” and may


Neurology_Adams

Neurology_Adams. and cancer associated retinopathy is frequently associated with photopsias prior to visual loss. Retinal toxicity from digitalis causes chromatopsia with a characteristic “yellowish vision” and may also cause photopsias. In patients with migraine, cortical spreading depression through the occipital lobe gives rise to the bright zigzag lines of a fortification spectrum. Stimulation of the cortical visual pathways accounts for stereotyped, repetitive simple or unformed visual hallucinations in epilepsy. Formed or complex visual hallucinations (of people, animals, landscapes) are observed in a variety of conditions, notably in old age when vision fails (Charles Bonnet syndrome, discussed in “Visual Hallucinations” in Chap. 21), with infarcts of the occipitoparietal or occipitotemporal regions (release hallucinations), in the withdrawal state following chronic intoxication with alcohol and other sedative-hypnotic drugs (see Chap. 41), and with lesions in the diencephalon (“peduncular


Neurology_Adams

Neurology_Adams. (release hallucinations), in the withdrawal state following chronic intoxication with alcohol and other sedative-hypnotic drugs (see Chap. 41), and with lesions in the diencephalon (“peduncular hallucinosis”). These disorders are also discussed in Chap. 21.


Neurology_Adams

Neurology_Adams. Occasionally, patients with a parietal lesion may perceive transposition of images, flipped across the vertical or horizontal axes (visual allesthesia), or a visual image may persist for minutes to hours or reappear episodically, after the exciting stimulus has been removed (palinopsia mentioned earlier). Polyopia, the perception of multiple images when a single stimulus is presented, is said to be associated predominantly with right occipital lesions and can occur with either eye. Usually there is one primary and a number of secondary images, and their relationships may be constant or changing. Bender and Krieger, who described several such patients, attributed the polyopia to unstable fixation. Oscillopsia, or illusory movement of the environment, is a perception caused by nystagmus and occurs mainly with lesions of the labyrinthine-vestibular apparatus; it is described with disorders of ocular movement. In patients describing intermittent monocular oscillopsia, myokymia of one


Neurology_Adams

Neurology_Adams. and occurs mainly with lesions of the labyrinthine-vestibular apparatus; it is described with disorders of ocular movement. In patients describing intermittent monocular oscillopsia, myokymia of one superior oblique muscle should be considered (see “Fourth Nerve Palsy” in Chap. 13).


Neurology_Adams

Neurology_Adams. Chapter 21 further discusses the clinical effects and syndromes that result from occipital lobe lesions. Amblyopia Because of Early Life Strabismus (Amblyopia Ex Anopsia)


Neurology_Adams

Neurology_Adams. As noted in the introductory part of this chapter, the generic term “amblyopia” has been adopted for a special circumstance in which a normal eye fails to acquire its potential visual acuity because images are not properly projected onto the fovea during a formative period of cerebral development. It is a disorder, as in the quip by van Noorden and Campos, “in which the patient sees nothing and the doctor sees nothing,” meaning that the pupillary response and fundus are observed to be normal despite the visual deficit. The degradation of vision and disuse of the fovea may be the result of a number of processes, including misaligned ocular axes (strabismus), reduced monocular inputs (deprivation, from ptosis or cataract), or unequal refractive errors (anisometropia; discussed in Chap. 13). The period of risk is during the first 7 years but is greatest in the earlier part of this epoch, and the visual loss may still be rectifiable beyond the time.


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Neurology_Adams. The developmental deficiency in the occipital cortex that gives rise to amblyopia has been extensively studied in animals and humans; a discussion of the subject can be found in numerous texts including the one by van Noorden and Campos. Neurologists should be aware that screening children for the disorder is highly valuable even if treatment is not always successful. The correction of refractive errors, cataract, and other correctible ocular problems are attended to first. Attempts are then made to force the utilization of the disadvantaged eye in preference to the normal one; patching and atropine drops are the typical methods to accomplish this. Other techniques of management and a summary of clinical trials of each can be found in the review by Holmes and Clarke. Chapter 14 discusses the problem of strabismus and the latent phorias that create confusion in the neurologic examination. Antonetti DA, Klein R, Gardner TW: Diabetic Retinopathy. N Engl J Med 366:1227, 2012.


Neurology_Adams

Neurology_Adams. Antonetti DA, Klein R, Gardner TW: Diabetic Retinopathy. N Engl J Med 366:1227, 2012. Arruga J, Sanders M: Ophthalmologic findings in 70 patients with evidence of retinal embolism. Ophthalmology 89:1336, 1982. Bender MB, Krieger HP: Visual function in perimetric blind fields. Arch Neurol Psychiatry 65:72, 1951. Benton S, Levy I, Swash M: Vision in the temporal crescent in occipital infarction. Brain 103:83, 1980. Biousse V, Newman NJ: Neuro-Ophthalmology Illustrated. Thieme, New York, 2009. Blythe IM, Kennard C, Ruddock KH: Residual vision in patients with retrogeniculate lesions of the visual pathways. Brain 110:887, 1987. Brown GC, Tasman WS: Congenital Anomalies of the Optic Disc. New York, Grune & Stratton, 1983. Chester EM: The Ocular Fundus in Systemic Disease. Chicago, Year Book, 1973. Corbett JJ: Neuro-ophthalmologic complications of hydrocephalus and shunting procedures. Semin Neurol 6:111, 1986.


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Neurology_Adams. Chester EM: The Ocular Fundus in Systemic Disease. Chicago, Year Book, 1973. Corbett JJ: Neuro-ophthalmologic complications of hydrocephalus and shunting procedures. Semin Neurol 6:111, 1986. Damasio AR: Disorder of complex visual processing: Agnosia, achromatopsia, Balint’s syndrome and related difficulties of orientation and construction. In: Mesulam M-M (ed): Principles of Behavioral Neurology. Philadelphia, Davis, 1985, pp 259–288. DeJong PT: Age-related macular degeneration. N Engl J Med 355:1474, 2006. Digre KB, Kurcan FJ, Branch DW, et al: Amaurosis fugax associated with antiphospholipid antibodies. Ann Neurol 25:228, 1989. Dryja TP, McGee TL, Reichel E, et al: A point mutation of the rhodopsin gene in one form of retinitis pigmentosa. Nature 343:364, 1990. Fisher CM: Observations on the fundus in transient monocular blindness. Neurology 9:333, 1959. Goodale MA, Milner AD:Separate visual pathways for perception and action. Trends in Neurosci. 15:20, 1992.


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Neurology_Adams. Goodale MA, Milner AD:Separate visual pathways for perception and action. Trends in Neurosci. 15:20, 1992. Grant WM: Toxicology of the Eye. Springfield, IL, Charles C Thomas, 1986. Grunwald GB, Klein R, Simmonds MA, Kornguth SE: Autoimmune basis for visual paraneoplastic syndrome in patients with small cell lung carcinoma. Lancet 1:658, 1985. Hayreh SS: Anterior ischemic optic neuropathy. Arch Neurol 38:675, 1981. Hayreh SS: Blood supply of the optic nerve head and its role in optic atrophy, glaucoma, and oedema of the optic disc. Br J Ophthalmol 53:721, 1969. Hayreh SS: Pathogenesis of oedema of the optic disc (papillo-edema). Br J Ophthalmol 48:522, 1964. Holmes JM, Clarke MP: Amblyopia. Lancet 367:1343, 2006. Horton JC: Wilbrand’s knee of the primate optic chiasm is an artefact of monocular enucleation. Trans Am Ophthalmol Soc 95:579, 1997. Hubel DH, Wiesel TN: Functional architecture of macaque monkey visual cortex. Proc R Soc Lond B Biol Sci 198:1, 1977.


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Neurology_Adams. Hubel DH, Wiesel TN: Functional architecture of macaque monkey visual cortex. Proc R Soc Lond B Biol Sci 198:1, 1977. Jacobson DM: The localizing value of a quadrantanopia. Arch Neurol 54:401, 1997. Jacobson DM, Thurkill CE, Tipping SJ: A clinical triad to diagnose paraneoplastic retinopathy. Ann Neurol 28:162, 1990. Jiang GL, Tucker SL, Guttenberger R, et al: Radiation-induced injury to the visual pathway. Radiother Oncol 30:17, 1994. Keane JR: Patterns of hysterical hemianopia. Neurology 51:1230, 1998. Kornguth SE, Klein R, Appen R, Choate J: The occurrence of anti-retinal ganglion cell antibodies in patients with small cell carcinoma of the lung. Cancer 50:1289, 1982. Lee LA, Roth S, Cheney FW, et al: The American Society of Anesthesiologists Postoperative Visual Loss Registry: Analysis of 93 spine surgery cases with postoperative visual loss. Anesthesiology 105:652, 2006.


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Neurology_Adams. Levin BE: The clinical significance of spontaneous pulsations of the retinal vein. Arch Neurol 35:37, 1978. Levine DN, Warach J, Farrah M: Two visual systems in mental imagery: Dissociation of “what” and “where” in imagery disorders due to bilateral posterior cerebral lesions. Neurology 35:1010, 1985. Marshall J, Meadows S: The natural history of amaurosis fugax. Brain 91:419, 1968. Meienberg O: Sparing of the temporal crescent in homonymous hemianopia and its significance for visual orientation. Neuroophthalmology 2:129, 1981. Minckler DS, Tso MOM, Zimmerman LE: A light microscopic autoradiographic study of axoplasmic transport in the optic nerve head during ocular hypotony, increased intraocular pressure, and papilledema. Am J Ophthalmol 82:741, 1976. Pandit RJ, Gales K, Griffiths PG: Effectiveness of testing of visual fields by confrontation. Lancet 358:1339, 2001.


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Neurology_Adams. Pandit RJ, Gales K, Griffiths PG: Effectiveness of testing of visual fields by confrontation. Lancet 358:1339, 2001. Pomeranz HD, Smith KH, Hart WM, Egan RA: Nonarteritic ischemic optic neuropathy developing soon after use of sildenafil (Viagra): A report of seven cases. J Neuroophthalmol 25:9, 2005. Rizzo JF, Lessell S: Optic neuritis and ischemic optic neuropathy. Arch Ophthalmol 109:1668, 1999. Rucker CW: Sheathing of retinal venous in multiple sclerosis. Mayo Clin Proc 47:335, 1972. Sadun RA, Martone JF, Muci-Mendoza R, et al: Epidemic optic neuropathy in Cuba: Eye findings. Arch Ophthalmol 112:691, 1994. Schumacher M, Schmidt D, Jurklies B, et al: Central retinal artery occlusion: local intra-arterial fibrinolysis versus conservative treatment, a multicenter randomized trial. Ophthalmology 117:1367, 2010. Slavin M, Glaser JS: Acute severe irreversible visual loss with sphenoethmoiditis-posterior orbital cellulitis. Arch Ophthalmol 105:345, 1987.


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Neurology_Adams. Slavin M, Glaser JS: Acute severe irreversible visual loss with sphenoethmoiditis-posterior orbital cellulitis. Arch Ophthalmol 105:345, 1987. The Cuba Neuropathy Field Investigation Team: Epidemic optic neuropathy in Cuba—clinical characteristics and risk factors. N Engl J Med 333:1176, 1995. Traquair HM. An Introduction to Clinical Perimetry. St. Louis, CV Mosby, 1948. Tso MOM, Hayreh SS: Optic disc edema in raised intracranial pressure: III. A pathologic study of experimental papilledema. Arch Ophthalmol 95:1448, 1977. Tso MOM, Hayreh SS: Optic disc edema in raised intracranial pressure: IV: Axoplasmic transport in experimental papilledema, Arch Ophthalmol 95:1458, 1977. Ungerleider LG, Mishkin M. Two cortical visual systems. In: Ingle DJ and Goodale MA, and Mansfield RJW (eds.): Analysis of visual behavior, Cambridge, MA: MIT press. Van Noorden GK, Campos E: Binocular Vision and Ocular Motility, 6th ed. St. Louis, Mosby, 2002.


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Neurology_Adams. Van Noorden GK, Campos E: Binocular Vision and Ocular Motility, 6th ed. St. Louis, Mosby, 2002. Weiskrantz L, Warrington EK, Sanders MD, Marshall J: Visual capacity in the hemianopic field following a restricted occipital ablation. Brain 97:709, 1974. Winterkorn J, Kupersmith MJ, Wirtschafter JD, Forman S: Treatment of vasospastic amaurosis fugax with calcium-channel blockers. N Engl J Med 329:396, 1993. Young LHY, Appen RE: Ischemic oculopathy. Arch Neurol 38:358, 1981. Figure 12-1. A. Conventional Snellen chart and B. Jaeger card for the estimation of visual acuity. The Snellen chart is placed 20 ft from the subject. The Jaeger card is used at 16 in from the subject’s eyes and approximates Snellen acuity if convergence and accommodation are normal.


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Neurology_Adams. Figure 12-2. Diagram showing the effects on the fields of vision produced by lesions at various points along the optic pathway. A. Complete blindness in left eye from an optic nerve lesion. B. A left “junctional scotoma” with vision loss in the left eye coupled with a superotemporal defect in the right eye. C. Chiasmatic lesion causing bitemporal hemianopia. D. Right homonymous hemianopia from optic tract lesion. E and F. Right superior and inferior quadrant hemianopia from interruption of visual radiations. G. Right homonymous hemianopia caused by lesion of occipital striate cortex. H. Hemianopia with macular sparing, typically from posterior cerebral artery infarction.


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Neurology_Adams. Figure 12-3. Diagram of the cellular elements of the retina. Light entering the eye anteriorly passes through the full thickness of the retina to reach the rods and cones (first system of retinal neurons). Impulses arising in these cells are transmitted by the bipolar cells (second system of retinal neurons) to the ganglion cell layer. The third system of visual neurons consists of the ganglion cells and their axons, which run uninterruptedly through the optic nerve, chiasm, and optic tracts, synapsing with cells in the lateral geniculate body. (Courtesy of Dr. E.M. Chester.) LateralventricleChiasmTemporal horn(Meyer’s loop)CalcarineareaTemporaldetourOpticnerveOpticradiationLat. geniculatebodyOptictract Figure 12-4. The geniculocalcarine projection, showing the detour of lower fibers around the temporal horn. Note that a very small proportion of the pathway traverses the parietal lobe.


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Neurology_Adams. Figure 12-4. The geniculocalcarine projection, showing the detour of lower fibers around the temporal horn. Note that a very small proportion of the pathway traverses the parietal lobe. Figure 12-5. Diagrammatic depiction of the retinal projections, showing the disproportionately large representation of the macula in the lateral geniculate nucleus and visual (striate) cortex. (Redrawn by permission from Barr ML, Kiernan J: The Human Nervous System, 4th ed. Philadelphia, Lippincott, 1983.) Figure 12-6. Hypertensive retinopathy, showing optic disc edema, cotton wool spots, hard exudates, and intraretinal hemorrhages. Figure 12-7. Preretinal (subhyaloid) hemorrhage extending through the macular of the left eye, precipitated by strong Valsalva maneuvering.


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Neurology_Adams. Figure 12-7. Preretinal (subhyaloid) hemorrhage extending through the macular of the left eye, precipitated by strong Valsalva maneuvering. Figure 12-8. Appearance of the fundus in central retinal artery occlusion. In addition to the paucity of blood flow in retinal vessels, the retina has a creamy gray appearance, and there is a “cherry-red spot” at the fovea. (Courtesy of Dr. Shirley Wray.) Figure 12-9. Glistening “Hollenhorst plaque” occlusion of a superior retinal artery branch (arrow). These occlusions represent atheromatous particles or, less often, platelet-fibrin emboli. Some are asymptomatic and others are associated with segmental visual loss or are seen after central retinal artery occlusion. (Courtesy of Dr. Shirley Wray.) Figure 12-10. Occlusion of the central retinal vein with suffusion of the veins, swelling of the disc, and florid retinal hemorrhages. (Courtesy of Dr. Shirley Wray.)


Neurology_Adams

Neurology_Adams. Figure 12-10. Occlusion of the central retinal vein with suffusion of the veins, swelling of the disc, and florid retinal hemorrhages. (Courtesy of Dr. Shirley Wray.) Figure 12-11. Mild papilledema with hyperemia of the disc and slight blurring of the disc margins. (Courtesy of Dr. Shirley Wray.) Figure 12-12. Fully developed papilledema. The main characteristics are marked swelling and enlargement of the disc, vascular engorgement, obscuration of small vessels at the disc margin as a result of nerve-fiber edema, and white “cotton-wool spots” that represent superficial infarcts of the nerve-fiber layer. (Courtesy of Dr. Shirley Wray.) Figure 12-13. Chronic papilledema with beginning optic atrophy, in which the disc stands out like a champagne cork. The hemorrhages and exudates have been absorbed, leaving a glistening residue around the disc. (Courtesy of Dr. Shirley Wray.)


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Neurology_Adams. Figure 12-14. Acute optic neuritis. Right, The disc is mildly swollen from an inflammatory process near the nerve head (papillitis). Left, MRI of the orbits with fat-saturation shows pathologic contrast enhancement of the right optic nerve. Figure 12-15. Nonarteritic anterior ischemic optic neuropathy (NAION) related to hypertension and diabetes. There is diffuse disc swelling from infarction that extends into the retina as a milky edema. The veins are engorged. “Cotton-wool” infarcts can be seen to the left of the disc and a “flame” hemorrhage extends from the right disc margin. Chapter 12 Disturbances of Vision Disorders of Ocular Movement and Pupillary Function


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Neurology_Adams. Chapter 12 Disturbances of Vision Disorders of Ocular Movement and Pupillary Function Ocular movement and vision are virtually inseparable. A moving object automatically evokes movement of the eyes and almost simultaneously enhances attention and perception. To visually search, that is, to peer, requires coordinated eye movements interspersed with periods of stable fixation of the visual image on the center of the two retinas. One might say that the ocular muscles are at the service of vision.


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Neurology_Adams. Abnormalities of ocular movement are of three basic types. One category can be traced to a lesion of the extraocular muscles themselves, the neuromuscular junction, or to the cranial nerves that supply them (nuclear or infranuclear palsy). The second type is a derangement in the highly specialized neural mechanisms that enable the eyes to move together (supranuclear and internuclear palsies). This distinction, in keeping with the general concept of upper and lower motor neuron paralysis, hardly portrays the complexity of the neural mechanisms governing ocular motility. Perhaps more common but not primarily neurologic is a third group of disorders, congenital strabismus, in which there is an imbalance of the yoked muscles of extraocular movement. This early ocular misalignment is one cause of a developmental reduction in monocular vision (amblyopia), as discussed at the end of the previous chapter.


Neurology_Adams

Neurology_Adams. In no aspect of human anatomy and physiology is the sensory guidance of muscle activity more instructively revealed than in the neural control of coordinated ocular movement. Moreover, the entirely predictable and “hard-wired” nature of the central and peripheral oculomotor apparatus allows for a very precise localization of lesions within these pathways. To focus the eyes voluntarily, to stabilize objects for scrutiny when one is moving, to bring into sharp focus near and far objects—all require the perfect coordination of six sets of extraocular muscles and three sets of intrinsic muscles (ciliary muscles, sphincters, and dilators of the iris). The neural mechanisms that govern these functions reside mainly in the midbrain and pons, but are greatly influenced by centers in the medulla, cerebellum, basal ganglia, and the frontal, parietal, and occipital lobes of the brain. Most of the nuclear structures and pathways concerned with fixation and stable ocular movements are now known


Neurology_Adams

Neurology_Adams. cerebellum, basal ganglia, and the frontal, parietal, and occipital lobes of the brain. Most of the nuclear structures and pathways concerned with fixation and stable ocular movements are now known and much has been learned of their physiology both from clinical-pathologic correlations in humans and from experiments in monkeys.


Neurology_Adams

Neurology_Adams. Accurate binocular vision is actually achieved by the associated action of all the ocular muscles. Several terms are used, somewhat interchangeably but with different specific meanings to describe these movements. The term duction denotes the movement of one eye in a single direction. The synchronous movement of both eyes is a version. The commonly used term, conjugate gaze, simply indicates that the eyes are aligned and move in the same direction. Therefore, the simultaneous movement of the eyes in opposing directions is dysconjugate, or disjunctive. Dysconjugate movements are either convergent or divergent. Convergent movements are required when one looks at a near object. At the same time, the pupils constrict and the ciliary muscles relax to thicken the lens and allow near vision (the accommodative-near reflex, or triad). Divergence is required for distant vision.


Neurology_Adams

Neurology_Adams. Rapid voluntary conjugate movements of the eyes to the opposite side are initiated in area 8 of the frontal lobe (see Fig. 21-2) and relayed to the pons. These quick movements, whose peak velocity may exceed 700 degrees per second, are termed saccades. Their purpose is to rapidly change ocular fixation and bring images of new objects of interest onto the foveae. Saccades are so rapid that there is no subjective awareness of movement during the change in eye position. Saccadic movements can be elicited by instructing an individual to look to the right or left (commanded saccades), or to move the eyes to a target (refixation saccades). These two movements are sometimes differently affected in neurologic disease. Saccades may also be elicited reflexively, as when a sudden sound or the appearance of an object in the peripheral field of vision attracts attention and triggers an automatic movement of the eyes in the direction of the stimulus. Saccadic latency, the interval between the


Neurology_Adams

Neurology_Adams. of an object in the peripheral field of vision attracts attention and triggers an automatic movement of the eyes in the direction of the stimulus. Saccadic latency, the interval between the appearance of a target and the initiation of a saccade, is approximately 200 ms.


Neurology_Adams

Neurology_Adams. The neurophysiologic pattern of pontine neurons that produces a saccade has been characterized as “pulse-step” in type. This refers to the sudden increase in neuronal firing (the pulse) that is necessary to overcome the inertia and viscous drag of the eyes and move them into their new position; it is followed by a return to a new baseline firing level (the step), which maintains the eyes in their new, eccentric position by tonic contraction of the extraocular muscles (gaze holding).


Neurology_Adams

Neurology_Adams. Saccades are distinguished from the slower and smoother pursuit movements, for which the major stimulus is a moving target. The function of pursuit movements is to stabilize the image of an object that is moving relative to the position of the head and eyes, thus maintaining a continuous clear image of the object on the fovea. Unlike saccades, pursuit movements to each side are generated in the ipsilateral parietooccipital cortex, with modulation by the ipsilateral cerebellum, especially the vestibulocerebellum (flocculus and nodulus).


Neurology_Adams

Neurology_Adams. When following a moving target, as the visual image slips off the foveae, the firing rate of the governing motor neurons increases in proportion to the speed of the target, so that eye velocity matches target velocity. If the eyes fall behind the target, supplementary catch-up saccades are required for refixation. In this situation, the pursuit movement is not smooth, but becomes jerky (“saccadic” pursuit). A lesion of one cerebral hemisphere may cause pursuit movements to that side to break up into saccades. Diseases of the basal ganglia also commonly disrupt pursuit into a ratchet-like saccadic pursuit in all directions.


Neurology_Adams

Neurology_Adams. If a series of visual targets enters the visual field, as when one is watching trees from a moving car or the stripes on a rotating drum, involuntary repeated quick saccades refocus the eyes centrally; the resulting cycles of pursuit and refixation are termed optokinetic nystagmus. This phenomenon is used as a bedside test, the main value of which is in revealing a lesion of the ipsilateral posterior parietal lobe. It may also be found that a frontal lobe lesion eliminates the quick nystagmoid refixation phase away from the side of the lesion, thereby causing the eyes to continue to follow the target until it is out of view. This optokinetic phenomenon is described more fully further on, in the section on nystagmus.


Neurology_Adams

Neurology_Adams. Vestibular influences are of particular importance in stabilizing images on the retina during head and body movement. By means of the vestibuloocular reflex (VOR), a prompt short latency movement of the eyes is produced that is equal and opposite to movement of the head. During sustained rotation of the head, the VOR is supplemented by the optokinetic system, which enables one to maintain compensatory eye movements for a more prolonged period. If the VOR is lost, as occurs with disease of the vestibular apparatus or eighth nerve, the slightest movements of the head, especially those occurring during locomotion, cause a movement of images across the retina large enough to impair vision. A unilateral loss of the VOR strongly implicates a disease of the vestibular apparatus on the side toward the rotation of the head. When objects are tracked using both eye and head movements, the VOR must be suppressed, otherwise the eyes would remain fixed in space; to accomplish this, the smooth


Neurology_Adams

Neurology_Adams. toward the rotation of the head. When objects are tracked using both eye and head movements, the VOR must be suppressed, otherwise the eyes would remain fixed in space; to accomplish this, the smooth pursuit signals cancel the unwanted vestibular ones (Leigh and Zee). It follows that the inability to suppress the VOR, while viewing a target moving with the patient’s head or body, is indicative of a defect of supranuclear pursuit.


Neurology_Adams

Neurology_Adams. As already mentioned, the signals for volitional horizontal gaze saccades originate in the eye field of the opposite frontal lobe (area 8 of Brodmann, see Fig. 21-2) and are modulated by the adjacent supplementary motor eye field and by the posterior visual cortical areas. Leichnetz traced the cortical-to-pontine pathways for saccadic horizontal gaze in the monkey. These fibers traverse the internal capsule and separate at the level of the rostral diencephalon into two bundles, the first being a primary ventral “capsular–peduncular” bundle, which descends through the most medial part of the cerebral peduncle. This more ventral pathway undergoes a partial decussation in the low midbrain, at the level of the trochlear nucleus, and terminates mainly in the vaguely defined paramedian pontine reticular formation (PPRF) of the opposite side, neurons of which, in turn, project to the adjacent sixth nerve nucleus (Fig. 13-1). A second, more dorsal “transthalamic” bundle is predominantly


Neurology_Adams

Neurology_Adams. reticular formation (PPRF) of the opposite side, neurons of which, in turn, project to the adjacent sixth nerve nucleus (Fig. 13-1). A second, more dorsal “transthalamic” bundle is predominantly uncrossed and courses through the internal medullary lamina and paralaminar parts of the thalamus to terminate diffusely in the pretectum, superior colliculus, and periaqueductal gray matter. An off-shoot of these fibers (the prefrontal oculomotor bundle) projects to the rostral part of the oculomotor nucleus and to the ipsilateral rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF) and to the interstitial nucleus of Cajal (INC), which are involved in vertical eye movements, as discussed in the next section.


Neurology_Adams

Neurology_Adams. The pathways for smooth pursuit movements are less well defined. One probably originates in the posterior parietal cortex and the adjacent temporal and anterior occipital cortex (area MT of the monkey), descending to the ipsilateral dorsolateral pontine nuclei. Also contributing to smooth pursuit movements are projections from the frontal eye fields to the ipsilateral dorsolateral pontine nuclei. The latter, in turn, project to the flocculus and dorsal vermis of the cerebellum, which provide stability for the pursuit movements. However, for the purposes of clinical work, lesions of the posterior parietal cortex are the ones known to impair pursuit toward the damaged side. Part of the frontal eye fields have been shown experimentally to participate in pursuit eye movements, but the influence of this area on pursuit is far less than that of the parietal lobes and is insignificant clinically.


Neurology_Adams

Neurology_Adams. Conventionally, the term ocular motor nuclei refers to the nuclei of the third, fourth, and sixth cranial nerves; the term oculomotor nucleus refers to the third nerve nucleus alone. Ultimately, all pathways that mediate saccadic, pursuit, vestibular, and optokinetic movements in the horizontal plane converge on the pontine tegmental center for horizontal gaze, the PPRF. The PPRF projects to the sixth nerve nucleus to command horizontal eye movement. However, it is understood from animal experiments that supranuclear neural signals that encode smooth pursuit, and vestibular and optokinetic movements may bypass the PPRF and project independently to the abducens nuclei (Hanson et al). Also required for horizontal versional movements are the nuclei prepositus hypoglossi and their commissure, the medial vestibular nuclei, and pathways in the pontine and tegmentum of the brainstem that interconnect the ocular motor nuclei (Fig. 13-1).


Neurology_Adams

Neurology_Adams. The fiber bundle connecting the ipsilateral sixth and third nuclei, and connecting both these nuclei with the vestibular nuclei, is the medial longitudinal fasciculus (MLF), lying in the medial tegmentum of the brainstem. The fibers of the MLF emanating from the sixth nerve nucleus cross in the pons and ascend to the contralateral medial rectus subnucleus of the third nerve. In this way, the abduction of one eye is yoked to adduction of the opposite one to produce conjugate horizontal gaze (Fig. 13-1).


Neurology_Adams

Neurology_Adams. The abducens nucleus contains two groups of neurons, each with distinctive morphologic and physiologic properties: (1) the intranuclear abducens motor neurons, which innervate the ipsilateral lateral rectus muscle, and (2) abducens internuclear neurons, which project via the contralateral MLF to the medial rectus neurons of the opposite oculomotor nucleus. Conjugate lateral gaze is accomplished by the simultaneous activation of the ipsilateral lateral rectus, and the contralateral medial rectus, again, the latter through fibers that run in the medial portion of the MLF. Interruption of the MLF results in a discrete impairment or loss of adduction of the eye ipsilateral to the lesion, a sign referred to as internuclear ophthalmoplegia, the details of which are discussed further on (Fig. 13-1).


Neurology_Adams

Neurology_Adams. Two other ascending pathways between the pontine centers and the mesencephalic reticular formation have been traced: one traverses the central tegmental tract and terminates in the pretectum, in the nucleus of the posterior commissure; the other is a bundle separate from the MLF that passes around the nuclei of Cajal and Darkschewitsch to the riMLF. These nuclei are involved more in vertical gaze and are described in the following text. In addition, each vestibular nucleus projects onto the abducens nucleus and the MLF of the opposite side to generate the slow phase of the VOR.


Neurology_Adams

Neurology_Adams. Control of voluntary eye movements depends upon a hierarchy of cell stations and parallel pathways that do not project directly to ocular motor nuclei but to adjacent premotor or burst neurons, which discharge at high frequencies immediately preceding a saccade (Leigh and Zee). The premotor or burst neurons for horizontal saccades lie within the PPRF and those for vertical saccades in the riMLF (see below). Yet a third class of neurons (omnipause cells), lying in the midline of the pons, is involved in the inhibition of unwanted saccadic discharges. Nonetheless, in clinical work, the circuit that comprises in sequence (1) frontal lobe eye fields, (2) contralateral pontine PPRF, (3) abducens nucleus, (4) MLF, and (5) opposite oculomotor nucleus makes understandable a number of highly characteristic defects of horizontal ocular motion, as detailed in the remainder of the chapter.


Neurology_Adams

Neurology_Adams. In contrast to horizontal gaze, which is generated by unilateral aggregates of cerebral and pontine neurons, vertical eye movements, with few exceptions, are under bilateral control of the cerebral cortex and upper brainstem. The groups of nerve cells and fibers that govern upward and downward gaze, as well as torsional saccades, are situated in the pretectal areas of the midbrain and involve three integrated structures—the riMLF, the INC, and the nucleus and fibers of the posterior commissure (Fig. 13-2).


Neurology_Adams

Neurology_Adams. The riMLF lies at the junction of the midbrain and thalamus, at the rostral end of the medial longitudinal fasciculus, just dorsomedial to the rostral pole of the red nucleus. It functions as the “premotor” nucleus with “burst cells” for the production of fast (saccadic) vertical versional and torsional movements. Input to the riMLF arises both from the PPRF and the vestibular nuclei. Each riMLF projects mainly ipsilaterally to the oculomotor and trochlear nuclei, but each riMLF is also connected to its counterpart by fibers that traverse the posterior commissure. Bilateral lesions of the riMLF or of their interconnections in the posterior commissure are more common than unilateral ones, and cause a loss either of downward saccades or of all vertical saccades.


Neurology_Adams

Neurology_Adams. The INC is a small collection of cells that lies just caudal to the riMLF on each side. Each nucleus projects to the motor neurons of the opposite elevator muscles (superior rectus and inferior oblique) by fibers that cross through the posterior commissure, and it projects ipsilaterally and directly to the depressor muscles (inferior rectus and superior oblique). The functional role of the INC appears to be in holding eccentric vertical gaze, especially after a saccade; it is also integral to the vestibuloocular reflex. Lesions of the INC produce a vertical gaze-evoked and torsional nystagmus, an ocular tilt reaction, and probably slow all conjugate eye movements, mainly vertical ones.


Neurology_Adams

Neurology_Adams. Lesions of the posterior commissure interrupt signals crossing to and from the INC and the riMLF. A lesion here characteristically produces a paralysis of upward gaze and of convergence, often associated with mild mydriasis, accommodative loss, convergence nystagmus, lid retraction (Collier “tucked lid” sign), and, less commonly, ptosis. This constellation is the Parinaud syndrome, also referred to as the pretectal, dorsal midbrain, or sylvian aqueduct syndrome (see “Vertical Gaze Palsy” further on). In some instances, only a restricted combination of these signs is seen. The same syndrome may be produced by unilateral lesions of the posterior commissure, presumably by interrupting bidirectional connections from the riMLF and INC. With acute lesions of the commissure, there is a tonic downward deviation of the eyes and lid retraction (“setting-sun sign”).


Neurology_Adams

Neurology_Adams. The MLF is the main conduit of signals that control vertical gaze from the vestibular nuclei in the medulla to the midbrain centers. For this reason, with internuclear ophthalmoplegia, along with the characteristic adductor paresis on the affected side, vertical pursuit and the VOR are impaired. This is most evident when bilateral internuclear ophthalmoplegia is present. Vertical deviation of the ipsilateral eye (skew) may be seen in cases of unilateral internuclear ophthalmoplegia, as discussed further on.


Neurology_Adams

Neurology_Adams. There are important vestibulocerebellar influences on both smooth pursuit and saccadic movements (see also Chaps. 5 and 14). The flocculus and posterior vermis of the cerebellum receive abundant sensory projections from proprioceptors of the cervical musculature (responsive to head velocity), the retinas (sensitive to target velocity), proprioceptors of eye muscles (eye position and eye velocity), auditory and tactile receptors, and the superior colliculi and PPRF. Cerebellar efferents concerned with ocular movement project onto the vestibular nuclei. The latter, in turn, influence gaze mechanisms through several projection systems: one, for horizontal movements, consists of direct projections from the vestibular nuclei to the contralateral sixth nerve nucleus; another, for vertical movements, projects via the contralateral MLF to third and fourth nerve nuclei (Figs. 13-1 and 13-2).


Neurology_Adams

Neurology_Adams. Lesions of the flocculus and posterior vermis are consistently associated with deficits in smooth pursuit movements and an inability to suppress the vestibuloocular reflex by fixation (Baloh et al). Floccular lesions are also an important cause of downbeat nystagmus. As indicated in Chap. 5, patients with cerebellar (floccular) lesions are unable to hold eccentric positions of gaze and must make repeated saccades to look at a target that is away from the neutral position (gaze-evoked nystagmus). This phenomenon is explained by the fact that with acute, one-sided lesions of the vestibulocerebellum, the inhibitory discharges of the Purkinje cells onto the ipsilateral medial vestibular nucleus are removed, and the eyes deviate away from the lesion. When gaze to the side of the lesion is attempted, the eyes drift back to the midline, and fixation can be corrected only by a saccadic jerk. The head and neck may also turn away from the lesion (the occiput toward the lesion and the face


Neurology_Adams

Neurology_Adams. attempted, the eyes drift back to the midline, and fixation can be corrected only by a saccadic jerk. The head and neck may also turn away from the lesion (the occiput toward the lesion and the face away). In addition, the vestibuloocular reflexes, which coordinate eye movements with head movements, are improperly adjusted (Thach and Montgomery). The interested reader can find further details concerning cerebellar influences on ocular movements in the monograph by Leigh and Zee and the review by Lewis and Zee.


Neurology_Adams

Neurology_Adams. Testing of Conjugate Gaze It is apparent from the foregoing remarks that there is considerable clinical information to be obtained from an analysis of ocular movements. To fully examine the eye movements, the patient should be asked to look quickly to each side as well as up and down (saccades) and to follow a moving target (pursuit of a light, the examiner’s finger, or an optokinetic drum). A patient with stupor and coma can be examined by passively turning the head or by irrigating the external auditory canals; these are vestibular stimuli to reflex eye movement as discussed in Chaps. 14 and 16.


Neurology_Adams

Neurology_Adams. Most individuals make accurate saccades to a target. Alterations of saccadic movements, particularly overshooting of the eyes (hypermetria), are characteristic of a cerebellar lesion. Slowness of saccadic movements is mainly the result of disease of the basal ganglia such as Huntington and Wilson diseases, ataxia-telangiectasia, progressive supranuclear palsy, multiple system atrophy, and certain lipid storage diseases. Lesions involving the PPRF may also be accompanied by slow saccadic movements to the affected side. Hypometric, slow saccades occurring only in the adducting eye indicate an incomplete internuclear ophthalmoparesis caused by a lesion of the ipsilateral MLF. When the earliest sign of a progressive eye movement disorder is slow saccades in the vertical plane, the likely diagnosis is progressive supranuclear palsy, but the same sign may occur in Parkinson disease and several less common processes that affect the basal ganglia, as discussed further on under “Vertical Gaze


Neurology_Adams

Neurology_Adams. is progressive supranuclear palsy, but the same sign may occur in Parkinson disease and several less common processes that affect the basal ganglia, as discussed further on under “Vertical Gaze Palsy.” Slow up-and-down saccades are also found in Niemann-Pick disease type C.


Neurology_Adams

Neurology_Adams. In addition to abnormalities of saccades velocity, saccadic latency or reaction time (the interval between the impulse to move and movement) is prolonged in Huntington chorea and Parkinson disease. Saccadic latency is also increased in corticobasal ganglionic degeneration (see Chap. 38), in which case it seems to correspond to the degree of motor apraxia. The obligate need to initiate eye movements with a blink is often a subtle sign of disordered supranuclear control of conjugate movements that is evident in these same diseases and in other processes including frontal lobe lesions.


Neurology_Adams

Neurology_Adams. Yet another saccadic disorder takes the form of an inability to initiate voluntary movements, either vertically or horizontally. This abnormality may be congenital in nature, as in the ocular “apraxia” of childhood (Cogan syndrome, see in the following text) and in ataxia-telangiectasia; an acquired difficulty in the initiation of saccadic movements may be seen in patients with Huntington disease or with a lesion of the contralateral frontal lobe or ipsilateral pontine tegmentum. Fragmentation of smooth pursuit movement, a frequent finding, is a jerky irregularity of tracking that has been called “saccadic pursuit.” Asymmetrical impairment of smooth pursuit movements is indicative of a parietal or a frontal lobe lesion. Pursuit is impaired toward the side of a parietal lesion and away from a frontal lesion. This clinical phenomenon can be elicited by optokinetic testing as explained further on.


Neurology_Adams

Neurology_Adams. In addition, impaired pursuit can arise from vestibulocerebellar and extrapyramidal disorders. The former is commonly the result of sedative drug intoxication—with barbiturates, diazepam, and others as well as from a lesion of the vestibulocerebellar apparatus. There can be gaze directed nystagmus that seemingly interrupts pursuit movements as well. A similar-appearing phenomenon, but one that does not manifest nystagmus, nicely called “cogwheel eye movements,” is seen in certain extrapyramidal diseases such as Parkinson disease, Huntington disease, and progressive supranuclear palsy. In these diseases, there is a ratchet-like impairment of smooth pursuit movements in association with slow, hypometric saccades (“saccadic pursuit”). Indeed, according to Vidailhet and colleagues, smooth pursuit movements are impaired in all types of basal ganglionic degenerations.


Neurology_Adams

Neurology_Adams. The VOR is tested by moving the patient’s head either horizontally or vertically while the individual maintains visual fixation on a distant stationary point. When the VOR is functioning normally, the eyes move automatically in the opposite direction to head turning (in fact they remain motionless in relation to the room and move only relative to the head). If the vestibular system is impaired, a head thrust will not elicit the normal contraversive eye movement. Instead, the eyes turn with the head, and the patient subsequently makes a “catch-up” saccade to return the eyes to the target of fixation. The saccade that refixates the eyes is observed more easily than is the slippage of the eyes from the target. Stimulation of the labyrinths by caloric or electrical activation also elicits reflexive eye movements, as described in Chap. 16 on Coma. When cold water is instilled into one ear, it simulates the physiology of the head turning the opposite direction. They eyes, therefore, make a


Neurology_Adams

Neurology_Adams. eye movements, as described in Chap. 16 on Coma. When cold water is instilled into one ear, it simulates the physiology of the head turning the opposite direction. They eyes, therefore, make a reflexive slow movement toward the cold stimulus. In an awake patient, this is accompanied by fast-phase movements (nystagmus) in the opposite direction, away from the cold stimulus.


Neurology_Adams

Neurology_Adams. Normally, movement of the head at a rate of one to two cycles per second does not cause blurring of vision because of the rapidity with which the VOR accomplishes compensatory eye movements. Dynamic visual acuity is a term applied to testing by having the patient read an eye chart while the head is rotated back-and-forth. A substantial drop in acuity occurring with head movements at this speed is indicative of failure of the VOR. Zee has described yet another means of testing the VOR in which the examiner observes the optic nerve head while the patient rotates the head back and forth. With a normal VOR, the optic disc does not appear to move since the eye’s position in space has remained unchanged. However, if the VOR is impaired, the optic nerve head appears to oscillate. Visual Fixation Reflex (Suppression of the Vestibuloocular Reflex)


Neurology_Adams

Neurology_Adams. Visual Fixation Reflex (Suppression of the Vestibuloocular Reflex) The ability to suppress the VOR by visual fixation provides considerable information and may be tested by rotating the patient in a chair while he fixates on the thumb of his outstretched hand. There should be no loss of fixation at moderate rotational speed. Nystagmus during this maneuver, reflecting the inability to suppress the VOR and maintain fixation, is an abnormal finding. As a result of inability to suppress the VOR, the patient experiences a feeling of instability. Impaired suppression of the VOR occurs with various disorders affecting cerebellar and brainstem circuits that maintain gaze stability; progressive supranuclear palsy and multiple sclerosis are two examples where this finding can be prominent. Testing the Near Response (Accommodative Triad)


Neurology_Adams

Neurology_Adams. Testing the Near Response (Accommodative Triad) Combined convergence and accommodative movements are tested by asking the patient to look at his thumbnail, the examiner’s finger, or object as it is brought toward the eyes. However, these fusional movements are frequently impaired in the elderly and in confused or inattentive patients and should not be interpreted as the result of disease in the ocular motor pathways. Otherwise, the absence or impairment of these movements should suggest a lesion in the rostral midbrain as a component of the Parinaud syndrome. Convergence spasm, which may mimic bilateral sixth nerve palsy, and retraction nystagmus may accompany paralysis of vertical gaze from a dorsal midbrain lesion. However, when such convergent spasms occur alone, they are usually nonorganic. Cycloplegic eye drops that abolish accommodation and pupillary miosis will sometimes abort psychogenic convergence spasm. Impairment of Conjugate Gaze


Neurology_Adams

Neurology_Adams. Impairment of Conjugate Gaze Strictly speaking, gaze palsy refers to a complete loss of both saccadic and pursuit movements to one side. Gaze paresis would then refer to an incomplete loss of the same capacities. Gaze palsies may be overcome by reflexive mechanisms, referring mainly to the VOR, when the disturbance affects the supranuclear inputs to the pontine gaze centers. In contrast, nuclear and infranuclear lesions cause an insurmountable impairment of gaze that cannot be overcome except perhaps by physically moving the globes (forced ductions).


Neurology_Adams

Neurology_Adams. As a rule, the horizontal gaze palsies of cerebral and pontine origin are readily distinguished by the side of an accompanying hemiparesis. When there is a tonic deviation of the eyes ipsilateral to a cerebral lesion, the eyes look toward the lesion and away from the hemiparesis. The opposite pertains to brainstem gaze palsies, that is, gaze is impaired toward the side opposite the lesion, and if there is gaze deviation, the eyes are turned toward a hemiparesis. Palsies of pontine origin need not have an accompanying hemiparesis but are associated with other signs of pontine disease, particularly peripheral facial palsies and internuclear ophthalmoplegia on the same side as the paralysis of gaze. Pontine gaze palsies tend to be longer lasting than those of cerebral origin. Also, in the case of a cerebral lesion (but not a pontine lesion), the eyes may turn to the paralyzed side if they are fixated on a target and the head is rotated passively to the opposite side (i.e., by utilizing


Neurology_Adams

Neurology_Adams. of a cerebral lesion (but not a pontine lesion), the eyes may turn to the paralyzed side if they are fixated on a target and the head is rotated passively to the opposite side (i.e., by utilizing the VOR).


Neurology_Adams

Neurology_Adams. Horizontal gaze palsy of cerebral origin An acute lesion of one frontal lobe, such as an infarct, usually causes impersistence or paresis of contralateral gaze (more so than an actual palsy of gaze), and the eyes may for a limited time turn involuntarily toward the side of the cerebral lesion. In most cases of acute frontal lobe damage, the gaze palsy is incomplete and temporary, lasting for a week or less. Almost invariably, it is accompanied by hemiparesis. Forced closure of the eyelids may cause the eyes to move paradoxically to the side of the hemiparesis (Cogan spasticity of conjugate gaze; although this finding is variable and of limited clinical value). Similarly, during sleep, the eyes may also deviate conjugately away from the side of the lesion toward the side of the hemiplegia. Pursuit movements away from the side of the lesion tend to be fragmented or lost. In contrast, posterior parietal lesions reduce ipsilateral pursuit movements but do not cause gaze palsy.


Neurology_Adams

Neurology_Adams. With bilateral frontal lesions, the patient may be unable to turn his eyes voluntarily in any direction but retains fixation and pursuit movements. Occasionally, a deep cerebral lesion, particularly a thalamic hemorrhage extending into the midbrain, will cause the eyes to deviate conjugately to the side opposite the lesion (“wrong-way” gaze); the basis for this anomalous phenomenon is not established, but interference with descending oculomotor tracts in the midbrain has been postulated by Tijssen. It should be emphasized that cerebral gaze paralysis is not attended by strabismus or diplopia, that is, gaze remains conjugate. The usual causes of gaze paresis are vascular occlusion with infarction, hemorrhage, and abscess or tumor of the frontal lobe.


Neurology_Adams

Neurology_Adams. A seizure originating in the frontal lobe may transiently drive the eyes to the opposite side, giving the impression of gaze palsy. In the postictal period, the direction of the gaze deviation may reverse with the eyes directed ipsilateral to the seizure focus. An unexplained phenomenon we have had the opportunity to observe is extreme deviation of the eyes to the side of induced visual hallucinations from an occipital seizure. This may also occur in a rare childhood form of occipital seizures. A unilateral lesion in the rostral midbrain tegmentum, by interrupting the cerebral pathways for horizontal conjugate gaze before their decussation, may also cause a supranuclear paresis of gaze to the opposite side. Vestibulocerebellar lesions can cause yet another disorder of conjugate gaze that simulates a gaze palsy in which the eyes are forced, or driven to one side in a manner termed “pulsion” that prevents voluntary movement to the other side.


Neurology_Adams

Neurology_Adams. Midbrain lesions affecting the pretectum and the region of the posterior commissure interfere with conjugate movements in the vertical plane. Paralysis of vertical gaze is a prominent feature of the Parinaud or dorsal midbrain syndrome described earlier. Upward gaze in general is affected far more frequently than downward gaze because, as already explained, some of the fibers subserving upgaze cross rostrally and posteriorly between the riMLF and INC and are subject to interruption before descending to the oculomotor nuclei, whereas the pathways for down-gaze apparently project directly downward to oculomotor nuclei from the two controlling centers.


Neurology_Adams

Neurology_Adams. The range of upward gaze is frequently restricted by extraneous factors, such as drowsiness, increased intracranial pressure, and particularly, aging. In a patient who cannot elevate the eyes voluntarily, the presence of reflex upward deviation of the eyes in response to flexion of the head (“doll’s-head maneuver”) or to voluntary forceful closure of the eyelids (Bell phenomenon) indicates that the nuclear and infranuclear mechanisms for upward gaze are intact and that the defect is supranuclear. However useful this rule may be, in some instances of disease of the peripheral neuromuscular apparatus—such as Guillain-Barré syndrome and myasthenia gravis—in which voluntary upgaze may be limited, the strong stimulus of eye closure may cause upward deviation, whereas voluntary attempts at upgaze are unsuccessful, thereby spuriously suggesting a lesion of the upper brainstem. In addition, approximately 15 percent of normal adults do not show a Bell phenomenon; in others, deviation of the


Neurology_Adams

Neurology_Adams. are unsuccessful, thereby spuriously suggesting a lesion of the upper brainstem. In addition, approximately 15 percent of normal adults do not show a Bell phenomenon; in others, deviation of the eyes is paradoxically downward.


Neurology_Adams

Neurology_Adams. In patients who during life had shown an isolated palsy of downward gaze, autopsy has disclosed bilateral lesions of the rostral midbrain tegmentum (just medial and dorsal to the red nuclei). An unusual case, described by Bogousslavsky and colleagues, suggests that a paralysis of vertical gaze may follow a strictly unilateral infarction that comprises the posterior commissure, riMLF, and INC. Hommel and Bogousslavsky have summarized the location of strokes that cause monocular and binocular vertical gaze palsies.


Neurology_Adams

Neurology_Adams. Several degenerative and related processes exhibit selective or prominent upgaze or vertical gaze palsies, as mentioned earlier (Table 13-1). In progressive supranuclear palsy, a highly characteristic feature is a selective paralysis of vertical gaze, with the more specific feature being downward paralysis beginning with impairment of saccades and later, restriction of all vertical movements. Parkinson and Lewy-body diseases (see Chap. 38), corticobasal ganglionic degeneration (see Chap. 38), and Whipple disease of the brain (see Chap. 31) may also produce vertical gaze palsies as these diseases progress. Other Supranuclear Disorders of Gaze


Neurology_Adams

Neurology_Adams. Other Supranuclear Disorders of Gaze The ocular tilt reaction, in which skew deviation (supranuclear vertical misalignment of the eyes, discussed further on) is combined with ocular torsion and head tilt, is attributed to an imbalance of otolithic-ocular and otolithic-colic reflexes. In lesions involving the vestibular nuclei, as occurs in lateral medullary infarction, the eye is lower on the side of the lesion. With lesions of the MLF or INC, which can also cause skew and an ocular tilt reaction, the eye is higher on the side of the lesion.


Neurology_Adams

Neurology_Adams. Another unusual disturbance of gaze is the oculogyric crisis, or spasm, which consists of a tonic spasm of conjugate deviation of the eyes, usually upward and less frequently, laterally or downward. Recurrent attacks, sometimes associated with spasms of the neck, mouth, and tongue muscles and lasting from a few seconds to an hour or two, were pathognomonic of postencephalitic parkinsonism in the past. Now this phenomenon is observed as an acute reaction in patients being given phenothiazine and related neuroleptic drugs and in Niemann-Pick disease. The pathogenesis of these ocular spasms is not known. The drug-induced form may be terminated by the administration of an anticholinergic medication such as benztropine.


Neurology_Adams

Neurology_Adams. Congenital oculomotor “apraxia” (Cogan syndrome) is a congential disorder characterized by an inability to make normal voluntary horizontal saccades when the head is stationary. Unusual eye and head movements are obligately tied together during attempts to change the position of the eyes. If the head is free to move and the patient is asked to look at an object to either side, the head is thrust to one side and the eyes turn in the opposite direction; the head overshoots the target, and the eyes, as they return to the central position, fixate on the target. Both voluntary saccades and the quick phase of vestibular nystagmus are defective. The pathologic anatomy is not understood but the condition abates over time. This same phenomenon is also seen in ataxia-telangiectasia (Louis-Bar disease, Chap. 37) and with agenesis of the corpus callosum.


Neurology_Adams

Neurology_Adams. Convergence insufficiency may give rise to diplopia and blurred vision at all near points; most cases are a result of head injury, some to encephalitis or multiple sclerosis. The ill-defined entity of divergence insufficiency causes diplopia at a distance because of crossing of the visual axes; in such patients images fuse only at a near position. This disorder may relate to changes in orbital fate and the position of the globe within the orbit. A special type of divergence paralysis, however, is seen with strokes in the rostral midbrain; these display an asymmetrical incompleteness of ocular abduction on both sides (pseudosixth palsy or convergence spasm). Based on scant clinical data, a center for active divergence has been postulated to reside in the rostral midbrain tegmentum.


Neurology_Adams

Neurology_Adams. The third (oculomotor), fourth (trochlear), and sixth (abducens) cranial nerves innervate the extrinsic muscles of the eye. Because their actions are closely integrated and many diseases involve all of them at once, they are suitably considered together.


Neurology_Adams

Neurology_Adams. The nuclei of the third (oculomotor) nerve consist of several paired groups of motor nerve cells adjacent to the midline, and ventral to the aqueduct of Sylvius at the level of the superior colliculi. A centrally located group of cells that innervate the pupillary sphincters and ciliary bodies (muscles of accommodation) is situated dorsally in the Edinger-Westphal nucleus; this is the parasympathetic portion of the oculomotor nucleus that subserves pupillary reactions to light and the near vision response. Ventral to this nuclear group are cells that mediate the actions of the levator of the eyelid, superior and inferior recti, inferior oblique, and medial rectus, in this dorsal–ventral order. This functional arrangement has been determined in cats and monkeys by extirpating individual extrinsic ocular muscles and observing the retrograde cellular changes (Warwick). Subsequent studies using radioactive tracer techniques have shown that medial rectus neurons occupy three disparate


Neurology_Adams

Neurology_Adams. extrinsic ocular muscles and observing the retrograde cellular changes (Warwick). Subsequent studies using radioactive tracer techniques have shown that medial rectus neurons occupy three disparate locations within the oculomotor nucleus rather than being confined to its ventral tip (Büttner-Ennever and Akert). These experiments also indicated that the medial rectus, inferior rectus, and the inferior oblique are innervated strictly ipsilaterally from the oculomotor nuclei, whereas the superior rectus receives only crossed fibers, and the levator palpebrae superioris (lid elevators) has bilateral innervations. Vergence movements are under the control of medial rectus neurons and not, as was once supposed, by an unpaired medial group of cells (nucleus of Perlia).


Neurology_Adams

Neurology_Adams. The fibers of the third-nerve nucleus course ventrally in the midbrain, crossing the medial longitudinal fasciculus, red nucleus, substantia nigra, and medial part of the cerebral peduncle successively. Lesions involving these structures therefore interrupt oculomotor fibers in their intramedullary (fascicular) course and give rise to several crossed syndromes with ipsilateral ocular palsy. With regard to the oculomotor subnuclei, schematic arrangements of their projections have been derived from various sources, mainly experimental but some clinical, and are shown in the figure from Ksiazek and colleagues (Fig. 13-3). The emerging fibers can be considered as situated in medial, lateral and rostrocaudal groups, with the pupillary fibers occupying the rostromedial aspect. This location of axons destined for the pupil continues through the third nerve. This information becomes useful in recognizing that combined pupillary and inferior and medial rectus palsies on one side may be the


Neurology_Adams

Neurology_Adams. of axons destined for the pupil continues through the third nerve. This information becomes useful in recognizing that combined pupillary and inferior and medial rectus palsies on one side may be the result of a fascicular lesion of the oculomotor nerve.


Neurology_Adams

Neurology_Adams. The oculomotor nerve, soon after it emerges from the brainstem, passes between the superior cerebellar and posterior cerebral arteries. The nerve (and sometimes the posterior cerebral artery) may be compressed at this point by herniation of the uncal gyrus of the temporal lobe through the tentorial opening (see Chap. 16). Just posterior and superior to the cavernous sinus, the oculomotor nerve crosses the terminal portion of the internal carotid artery at its junction with the posterior communicating artery. An aneurysm at this site frequently damages the third nerve; this serves to localize the site of compression or bleeding. When infraclinoid retrocavernous compressive lesions, such as aneurysms and tumors, affect the oculomotor nerve, they tend to also involve all three divisions of the trigeminal nerve. In the posterior portion of the cavernous sinus, the first and second trigeminal divisions are involved along with the ocular motor nerves; in the anterior portion, only the


Neurology_Adams

Neurology_Adams. of the trigeminal nerve. In the posterior portion of the cavernous sinus, the first and second trigeminal divisions are involved along with the ocular motor nerves; in the anterior portion, only the ophthalmic division of the trigeminal nerve is affected since the third trigeminal division does not pass through the cavernous sinus.


Neurology_Adams

Neurology_Adams. As the oculomotor nerve enters the orbit, it divides into superior and inferior branches, although a functional separation of nerve bundles occurs well before this anatomic bifurcation. The superior branch supplies the superior rectus and the voluntary (striated) part of the levator palpebrae (the involuntary part is under the control of sympathetic fibers of Müller); the inferior branch supplies the pupillary and ciliary muscles and all the other extrinsic ocular muscles except, of course, two—the superior oblique and the lateral rectus which are innervated by the trochlear and abducens nerves, respectively. Superior branch lesions of the oculomotor nerve caused by an aneurysm or more commonly by diabetes, result in ptosis and uniocular upgaze paresis.


Neurology_Adams

Neurology_Adams. The sixth (abducens) nerve arises at the level of the lower pons from a paired group of cells in the floor of the fourth ventricle, adjacent to the midline. The intrapontine portion of the facial nerve loops around the sixth-nerve nucleus before it turns anterolaterally to make its exit; a lesion in this locality therefore causes a homolateral paralysis of the lateral rectus and facial muscles. It is important to note that the efferent fibers of the oculomotor and abducens nuclei have a considerable intramedullary, that is, fascicular, portion (Fig. 13-4A and B). After leaving the brainstem, the nerve sweeps upward along the clivus and then runs alongside the third and fourth cranial nerves; together they course anteriorly, pierce the dura just lateral to the posterior clinoid process, and run in the lateral wall of the cavernous sinus, where they are closely applied to the internal carotid artery and first and second divisions of the fifth nerve (Fig. 13-5 and see “Cavernous Sinus


Neurology_Adams

Neurology_Adams. and run in the lateral wall of the cavernous sinus, where they are closely applied to the internal carotid artery and first and second divisions of the fifth nerve (Fig. 13-5 and see “Cavernous Sinus Thrombosis” in Chap. 33).


Neurology_Adams

Neurology_Adams. The cells of origin of the fourth (trochlear) nerve are just caudal to those of the oculomotor nerves in the lower midbrain. Unlike all other cranial nerves, the fourth nerve emerges from the dorsal surface of the lower midbrain and then decussates a short distance from its origin, just caudal to the inferior colliculi. The nerves proceed circumferentially and ventrally around the midbrain toward the entry of the nerve into the posterior cavernous sinus. Each nucleus therefore innervates the contralateral superior oblique muscle. The long extraaxial course and the position of the nerves adjacent to the brainstem is a putative explanation for the common complication of fourth-nerve palsy in head injury (see Chap. 34). The superior oblique muscle forms a tendon that passes through a pulley structure (the trochlea) and attaches to the upper aspect of the globe. When the eye is adducted, the muscle exerts an upward pull, but being attached to the globe behind the axis of rotation, it


Neurology_Adams

Neurology_Adams. structure (the trochlea) and attaches to the upper aspect of the globe. When the eye is adducted, the muscle exerts an upward pull, but being attached to the globe behind the axis of rotation, it causes depression and intorsion of the eye; in abduction, it pulls the ocular meridian toward the nose, thereby causing intorsion (i.e., clockwise in the right eye and counterclockwise in the left from the examiner’s perspective).


Neurology_Adams

Neurology_Adams. Together with the first division of the fifth nerve, the third, fourth, and sixth nerves enter the orbit through the superior orbital fissure.


Neurology_Adams

Neurology_Adams. Under normal conditions, all the extraocular muscles participate in every movement of the eyes; for proper movement, the contraction of any muscle requires relaxation of its antagonist. Clinically, however, an eye movement can be thought of in terms of the one muscle that is predominantly responsible for an agonist movement in that direction, for example, outward movement of the eye requires the action of the lateral rectus; inward movement, action of the medial rectus. The action of the superior and inferior recti and the oblique muscles varies according to the position of the eye. When the eye is turned outward, the elevator is the superior rectus and the depressor is the inferior rectus. When the eye is turned inward, the elevator and depressor are the inferior and superior oblique muscles, respectively. The actions of the ocular muscles in different positions of gaze are illustrated in Fig. 13-6 and Table 13-2.


Neurology_Adams

Neurology_Adams. The term binocular diplopia refers to the symptom of double vision caused by a misalignment of the visual axes of the two eyes. It is only present when both eyes are open and can see. Put another way, covering one eye usually obliterates double vision. In contrast, monocular diplopia persists when one eye is closed and is often due to lenticular or retinal disease or is nonorganic.


Neurology_Adams

Neurology_Adams. Strabismus, strictly speaking, refers to a muscle imbalance that results in misalignment of the visual axes, but the term is used most often to describe a congenital variety of misalignment. Strabismus may be caused by weakness of an individual eye muscle (paralytic strabismus) or by an imbalance of muscular tone, presumably because of a faulty “central” mechanism that normally maintains a proper angle between the two visual axes (nonparalytic or pediatric strabismus, see below). Almost everyone has a slight tendency toward strabismus that is referred to as a phoria and is normally overcome by the fusion mechanisms. A misalignment that is manifest during binocular viewing of a target and cannot be overcome is called a tropia. The ocular misalignment is overtly apparent by viewing the position of the patient’s eyes while they fixate on a distant target. When tested monocularly, the range of movement in the affected eye is essentially normal. The prefixes esoand exoindicate that the


Neurology_Adams

Neurology_Adams. of the patient’s eyes while they fixate on a distant target. When tested monocularly, the range of movement in the affected eye is essentially normal. The prefixes esoand exoindicate that the phoria or tropia is directed inward or outward, respectively, and the prefixes hyperand hypo-, that the deviation is upward or downward. Paralytic strabismus is primarily a neurologic problem; nonparalytic strabismus (referred to as comitant strabismus if the angle between the visual axes is the same in all fields of gaze) is usually managed by ophthalmologists, although it is associated with a number of congenital cerebral diseases and forms of developmental delay.


Neurology_Adams

Neurology_Adams. It is in this sense that the unqualified term strabismus is often used. The normal slight exotropia of neonates corrects by about 3 months of age. Large malalignments (> 15 degrees) are considered abnormal, even at birth. Most children with developmental esotropic strabismus present between ages 2 and 3 years, whereas those with exotropia show the condition in a broader range of preschool years. Esodeviations are initially intermittent and then become persistent; exodeviations are commonly intermittent. In both cases, eye movements are full and the child initially alternates fixation.


Neurology_Adams

Neurology_Adams. One type of esotropia, called accommodative esotropia, is typically an acquired problem that relates to hypermetropia (farsightedness) with compensatory engagement of the near response that drives the eyes to cross. Treatment with glasses within 6 months of the onset of the strabismus restores vision and usually leads to realignment of the axes. Large degrees of esotropia that are not the result of hypermetropia are best treated by surgical realignment.


Neurology_Adams

Neurology_Adams. In contrast, persistent exotropic strabismus in a child can be associated with a developmental delay, often as a component of a recognizable mental retardation syndrome, as detailed in Chap. 37, or with ocular pathology. It does, however, frequently occur in neurologically normal children. If mild, intermittent exotropia is initially treated by one of a number of nonsurgical means such as patching and visual exercises to stimulate convergence; surgical correction is reserved for unresponsive cases. Donahue has written an informative review of the subject.


Neurology_Adams

Neurology_Adams. Once binocular fusion is established, usually by 6 months of age, any type of ocular muscle imbalance will cause diplopia, as images then fall on disparate or noncorresponding parts of the two functionally active retinas. After a time, however, the child eliminates the diplopia by suppressing the image from one eye. After another variable period, the suppression becomes permanent, and the individual retains diminished visual acuity in that eye, the result of prolonged disuse (amblyopia ex anopsia), as described in the last portion of Chap. 12. Nonparalytic strabismus may create misleading ocular findings in the neurologic examination. Sometimes a slight phoric misalignment of the eyes is first noticed after a head injury or a febrile infection, or it may be exposed by any other neurologic disorder or drug intoxication that impairs fusional mechanisms (vergence).


Neurology_Adams

Neurology_Adams. In a cooperative patient, nonparalytic strabismus may be demonstrated by showing that each eye moves fully when the other eye is covered. Tropias and phorias can readily be detected by means of the simple “cover” and “cover–uncover” tests. When fusion is disrupted by covering one eye, the occluded eye will deviate; uncovering that eye results in a quick corrective movement designed to reestablish the fusion mechanism. Clinical Effects of Lesions of the Third, Fourth, and Sixth Nerves


Neurology_Adams

Neurology_Adams. A complete third nerve palsy includes ptosis, or drooping of the upper eyelid (as the levator palpebrae is supplied mainly by this nerve), and an inability to rotate the eye upward, downward, or inward. This corresponds to the weaknesses of the medial, superior, and inferior recti and the inferior oblique muscles. The remaining actions of the fourth and sixth nerves give rise to a position of the eye described by the mnemonic “down and out.” The patient experiences diplopia in which the image from the affected eye is projected upward and medially. In addition, one finds a dilated, nonreactive pupil (iridoplegia), and paralysis of accommodation (cycloplegia) because of interruption of the parasympathetic fibers in the third nerve. However, the extrinsic and intrinsic (pupillary) eye muscles may be affected separately in certain diseases. For example, a lesion affecting the central portion of the oculomotor nerve, as occurs in diabetic ophthalmoplegia, typically spares the pupil, as the


Neurology_Adams

Neurology_Adams. may be affected separately in certain diseases. For example, a lesion affecting the central portion of the oculomotor nerve, as occurs in diabetic ophthalmoplegia, typically spares the pupil, as the parasympathetic preganglionic pupilloconstrictor fibers lie near the surface. Conversely, compressive lesions of the nerve usually dilate the pupil as an early manifestation. After injury, regeneration of the third nerve fibers may be aberrant, in which case some of the fibers that originally moved the eye in a particular direction now reach another muscle or the iris; in the latter instance the pupil, which is unreactive to light, may constrict when the eye is turned up and in.


Neurology_Adams

Neurology_Adams. A lesion of the fourth nerve, which innervates the superior oblique muscle, is the most common cause of isolated symptomatic vertical diplopia. Although oculomotor palsy was a more common cause of vertical diplopia in Keane’s 1975 series, in instances where this is the sole complaint, trochlear palsy (and brainstem lesions) have predominated in our experience. Paralysis of the superior oblique muscle results in weakness of downward movement of the affected eye (Fig. 13-7E), so that the patient complains of special difficulty in reading or going down stairs. The affected eye tends to deviate slightly upward when the patient looks straight ahead and the upward deviation increases as that eye adducts on attempted horizontal gaze. In the presence of a third nerve palsy, one can assess the function of the fourth nerve by evaluating whether the eye intorts on attempted down gaze. Double vision from an isolated fourth neve palsy is worse with ipsilateral head tilt. Compensatory head tilting


Neurology_Adams

Neurology_Adams. of the fourth nerve by evaluating whether the eye intorts on attempted down gaze. Double vision from an isolated fourth neve palsy is worse with ipsilateral head tilt. Compensatory head tilting to the opposite shoulder (Bielschowsky sign) is especially characteristic of fourth-nerve lesions; this maneuver causes intorsion of the unaffected eye and ameliorates the double vision. Lesions affecting the trochlear nucleus (rather than the nerve itself) will cause paresis of the contralateral superior oblique muscle; here, the patient will tilt their head toward the side of the lesion to ameliorate the diplopia.


Neurology_Adams

Neurology_Adams. Bilateral trochlear palsies, as may occur after head trauma, give a characteristic alternating hyperdeviation depending on the direction of gaze (unilateral traumatic trochlear paresis is still the more common finding with head injury). A useful review of the approach to vertical diplopia is given by Palla and Straumann. Lesions of the sixth nerve result in a paralysis of the abducens muscle and a resultant weakness of lateral or outward movement leading to a crossing of the visual axes. The affected eye deviates medially, that is, in the direction of the opposing muscle. Diplopia is experienced as horizontal separation that is greatest when viewing in the direction of the sixth nerve palsy and in the distance (Fig 13-7A). With incomplete sixth nerve palsies, turning the head toward the side of the paretic muscle overcomes the diplopia.


Neurology_Adams

Neurology_Adams. Many causes of combined ocular motor palsies, which are discussed in a later section, are listed in Table 13-3 and are illustrated in Fig. 13-7 and in the following text. The Analysis of Diplopia


Neurology_Adams

Neurology_Adams. A common cause of binocular diplopia (i.e., seeing a single object as double) is an acquired paralysis or paresis of one or more extraocular muscles. The signs of the oculomotor palsies, as described previously, can manifest in various degrees of completeness. With complete palsies, the affected muscle can often be surmised from the resting dysconjugate positions of the globes. With incomplete paresis, noting the relative positions of the corneal light reflections and having the patient perform common versional movements will usually disclose the faulty muscle(s) as the eyes are turned into the field of action of the paretic muscle. The muscle weakness may be so slight, however, that no strabismus or defect in ocular movement is obvious, yet the patient experiences diplopia. It is then necessary to use the patient’s report of the relative positions of the images of the two eyes. Certain precautions should be taken in testing: one is cognizance of the absence of diplopia when the


Neurology_Adams

Neurology_Adams. necessary to use the patient’s report of the relative positions of the images of the two eyes. Certain precautions should be taken in testing: one is cognizance of the absence of diplopia when the visual axes are widely separated and, the object or light used for testing should not be obscured by the patient’s nose.


Neurology_Adams

Neurology_Adams. Two rules are applied sequentially to identify the affected ocular muscle in the analysis of diplopia: 1. The direction in which the images are maximally separated indicates the action of the pair of muscles at fault. For example, if the greatest horizontal separation is in looking to the right, either the right abductor (lateral rectus) or the left adductor (medial rectus) muscle is weak; if maximal when gazing to the left, the left lateral rectus and right medial rectus are implicated (Fig. 13-6A and B). As a corollary, if the separation is mainly horizontal, the paresis will be found in one of the horizontally acting recti (a small vertical disparity should be disregarded); if the separation is mainly vertical, the paresis will be found in the vertically acting muscles, and a small horizontal deviation should be disregarded.


Neurology_Adams

Neurology_Adams. 2. The second step in analysis identifies which of the two implicated muscles is responsible for the diplopia. The image projected farther from the center is attributable to the eye with the paretic muscle.


Neurology_Adams

Neurology_Adams. The simplest maneuver for the analysis of diplopia consists of asking the patient to follow an object or light into the six cardinal positions of gaze. When the position of maximal separation of images is identified, one eye is covered and the patient is asked to identify which image disappears. The red-glass test is an enhancement of this technique. A red glass is placed in front of the patient’s right eye (the choice of the right eye is arbitrary, but if the test is always done in the same way, interpretation is simplified). The patient is then asked to look at a flashlight (held at a distance of 1 m), to turn the eyes sequentially to the six cardinal points in the visual fields, and to indicate the positions of the red and white images and the relative distances between them. The positions of the two images are plotted as the patient indicates them to the examiner (i.e., from the patient’s perspective; Fig. 13-7). This allows the identification of both the field of maximal


Neurology_Adams

Neurology_Adams. positions of the two images are plotted as the patient indicates them to the examiner (i.e., from the patient’s perspective; Fig. 13-7). This allows the identification of both the field of maximal separation and the eye responsible for the eccentric image. If the white image on right lateral gaze is to the right of the red (i.e., the image from the left eye is projected outward), then the left medial rectus muscle is weak.


Neurology_Adams

Neurology_Adams. If the maximum vertical separation of images occurs on looking downward and to the left and the white image is projected farther down than the red, the paretic muscle is the left inferior rectus; if the red image (from the right eye) is lower than the white, the paretic muscle is the right superior oblique. As already mentioned, correction of vertical diplopia by a tilting of the head implicates the superior oblique muscle of the opposite side (or the ipsilateral trochlear nucleus). Separation of images on looking up and to the right or left will similarly distinguish paresis of the inferior oblique and superior rectus muscles. Most patients are attentive enough to open and close each eye and determine the source of the image thrown most outward in the field of maximal separation.


Neurology_Adams

Neurology_Adams. There are several alternative methods for studying the relative positions of the images of the two eyes. One, a refinement of the red-glass test, is the Maddox rod, in which the occluder consists of a transparent red lens with series of parallel cylindrical bars that transform a point source of light into a red line perpendicular to the cylinder axes. The position of the red line is easily compared by the patient with the position of a white point source of light seen with the other eye. Another technique, the alternate cover test, requires less cooperation than the red-glass test and is, therefore, a passive maneuver that is more useful in the examination of children and inattentive patients. It does, however, require sufficient visual function to permit central fixation with each eye. The test consists of rapidly alternating an occluder or the examiner’s hand from one eye to another and observing the deviations from and return to the point of fixation, as described earlier in the


Neurology_Adams

Neurology_Adams. The test consists of rapidly alternating an occluder or the examiner’s hand from one eye to another and observing the deviations from and return to the point of fixation, as described earlier in the chapter in the discussion of tropias and phorias. Measuring the prismatic correction needed to neutralize the ocular misalignment in each field of gaze with a prism bar allows the quantification of deviation and provides a method to follow diplopia over time.


Neurology_Adams

Neurology_Adams. The more sophisticated Lancaster test uses red/green glasses and a red and green bar of laser light projected on a screen to accomplish essentially the same result but has the advantage of reflecting the actual position and torsion of each eye. Detailed descriptions of the Maddox rod and alternate cover tests, which are the ones favored by neuroophthalmologists, can be found in the monographs of Leigh and Zee and of Glaser. In all these tests, the examiner is aided by committing to memory the cardinal actions of the ocular muscles shown in Fig. 13-6 and Table 13-2. The red-glass and other similar tests are most useful when a single muscle is responsible for the diplopia. If testing suggests that more than one muscle is involved, myasthenia gravis and thyroid ophthalmopathy are likely causes as they affect several muscles of ocular motility. Palsy of the oculomotor nerve causes a similar circumstance.


Neurology_Adams

Neurology_Adams. Monocular diplopia occurs most commonly in relation to diseases of the cornea and lens rather than the retina; usually the images are overlapping or superimposed rather than discrete. In most cases, monocular diplopia can be traced to a lenticular distortion or displacement but in some, no abnormality can be found and the symptom has a nonorganic basis. Monocular diplopia has been reported in association with cerebral disease (Safran et al), but this is a rare occurrence. Occasionally, patients with homonymous scotomas caused by a lesion of the occipital lobe will see multiple images (polyopia) in the defective field of vision, particularly when the target is moving. Causes of Individual Third, Fourth, and Sixth Nerve Palsies (Table 13-3)


Neurology_Adams

Neurology_Adams. Causes of Individual Third, Fourth, and Sixth Nerve Palsies (Table 13-3) Ocular palsies may have a central cause—that is, a lesion of the nucleus or the intramedullary (fascicular) portion of the cranial nerve—but more often they are peripheral. Weakness of ocular muscles because of a lesion in the brainstem is usually accompanied by involvement of other cranial nerves and by signs referable to the “crossed” brainstem syndromes of a cranial nerve palsy on one side and weakness or other deficits on the opposite side (see Table 33-3 and Chap. 44). Peripheral lesions, which may or may not be solitary, have a great variety of causes.


Neurology_Adams

Neurology_Adams. In the series reported by Rucker (1958, 1966), who analyzed 2,000 cases of paralysis of the oculomotor nerves, the most common sources of individual ocular motor palsies were tumors at the base of the brain or skull (primary, metastatic, meningeal carcinomatosis), head trauma, ischemic infarction of a nerve (generally associated with diabetes), and aneurysms of the circle of Willis, in that order. The sixth nerve was affected in about half of the cases; third-nerve palsies were about half as common; and the fourth nerve was involved in less than 10 percent of cases. In 1,000 unselected cases reported subsequently by Rush and Younge, trauma was a more frequent cause than neoplasm and the frequency of aneurysm-related cases was fewer than in the aforementioned series; otherwise the findings were similar. Less-common causes of paralysis of the oculomotor nerves, but nonetheless seen by most practitioners, include variants of Guillain-Barré syndrome, herpes zoster, giant cell arteritis,