Neurology_Adams

Neurology_Adams. Light entering the eye is focused by the cornea and then the biconvex lens onto the outer layer of the retina. The cornea, fluid of the anterior chamber, lens, vitreous, and retina itself must be transparent. The clarity of these media can be determined ophthalmoscopically, and a complete examination requires that the pupil be dilated to at least 6 mm in diameter. This is accomplished by instilling two drops of 2.5 percent phenylephrine and/or 0.5 to 1.0 percent tropicamide in each eye after the visual acuity has been measured, the pupillary response is recorded, and the intraocular pressure is estimated. In elderly persons, lower concentrations of these mydriatics should be used. The mydriatic action of phenylephrine lasts for 3 to 6 h. Rarely, an attack of angle-closure glaucoma (manifesting itself by diminished vision, ocular pain, nausea, and vomiting) may be precipitated by pharmacologic pupillary dilatation; this requires the administration of pilocarpine to the eye and the


Neurology_Adams

Neurology_Adams. itself by diminished vision, ocular pain, nausea, and vomiting) may be precipitated by pharmacologic pupillary dilatation; this requires the administration of pilocarpine to the eye and the immediate attention of an ophthalmologist. It is advisable to have access to pilocarpine if the pupils are to be dilated.


Neurology_Adams

Neurology_Adams. By looking through a high-plus lens of the direct ophthalmoscope from a distance of 6 to 12 in, the examiner can visualize opacities in the refractive media; by adjusting the lenses from a high-plus to a zero or minus setting, it is possible to “depth-focus” from the cornea to the retina. Depending on the refractive error of the examiner, lenticular opacities are best seen within the range of +20 to +12. The retina comes into focus with +1 to -1 lenses. The illuminated pupil appears as a red circular structure (red reflex), the color being provided by blood in the capillaries of the choroid layer. The main limit of direct ophthalmoscopy is its inability to visualize lesions in the retina that lie anterior to the equator of the globe; these are seen only by the indirect method. Testing for Abnormalities of the Visual Fields


Neurology_Adams

Neurology_Adams. Figure 12-2 illustrates the visual field defects caused by lesions of the retina, optic nerve and tract, lateral geniculate body, geniculocalcarine pathway, and striate cortex of the occipital lobe. In the alert, cooperative patient, the visual fields can be plotted fairly accurately at the bedside. With one of the patient’s eyes covered and the other fixed on the corresponding eye of the examiner (patient’s right with examiner’s left), a target—such as a moving finger, a cotton pledget, or a white disc mounted on a stick—is brought from the periphery toward the center of the visual field (confrontation testing). With the target at an equal distance between the eye of the examiner and that of the patient, the fields of the patient and examiner are then compared. Similarly, the patient’s blind spot can be aligned with the examiner’s, and its size determined by moving a small target outward from the blind spot until it is seen. For reasons not known, red-green test objects are more


Neurology_Adams

Neurology_Adams. blind spot can be aligned with the examiner’s, and its size determined by moving a small target outward from the blind spot until it is seen. For reasons not known, red-green test objects are more sensitive than white ones in detecting defects of the visual pathways.


Neurology_Adams

Neurology_Adams. Lesions of the macula, retina, or optic nerve cause a scotoma (an island of impaired vision surrounded by normal vision) rather than a defect that extends to the periphery of one visual field (“field deficit”). Scotomas are named according to their position (central, cecocentral) or their shape (ring, arcuate). A small scotoma that is situated in the macular part of the visual field may seriously impair visual acuity.


Neurology_Adams

Neurology_Adams. It should be emphasized that movement of the visual target provides the coarsest stimulus to the retina, so that a perception of its motion may be preserved while a stationary target of the same size may not be seen. In other words, moving targets are less useful than static ones in confrontational testing of visual fields. Finger counting and comparison of color intensity of a red object or the clarity of the examiner’s hand from quadrant to quadrant are simple confrontation tests that will disclose most field defects. Glaser recommends presenting the examiner’s hands simultaneously, one on each side of the vertical meridian; the hand in the hemianopic field appears blurred or darker than the other. Similarly, a scotoma may be defined by asking the patient to report changes in color or brightness of a red test object as it is moved toward or away from the point of fixation. A central scotoma may be identified by having the patient fix with one eye on the examiner’s nose, on which the


Neurology_Adams

Neurology_Adams. of a red test object as it is moved toward or away from the point of fixation. A central scotoma may be identified by having the patient fix with one eye on the examiner’s nose, on which the examiner places the index finger of one hand or a white-headed pin and has the patient compare it for brightness, clarity, and color with a finger or pin held in the periphery. In young children or uncooperative patients, the integrity of the fields may be roughly estimated by observing whether the patient is attracted to objects in the peripheral field or blinks in response to sudden threatening gestures in half of the visual field.


Neurology_Adams

Neurology_Adams. We continue to teach that these confrontation techniques are reasonably sensitive for routine clinical work if performed carefully, but we are mindful of the study from Pandit and colleagues, who found false-negative findings in 42 percent of patients tested with quadrant finger counting, using static automated perimetry as a standard. If any defect is found or suspected from confrontation testing, the fields should be charted and scotomas outlined on a tangent screen or perimeter. Although most automated perimetry techniques encompass only the central visual field, this method is usually adequate to detect most clinically important changes.


Neurology_Adams

Neurology_Adams. The method of testing by double simultaneous stimulation may elicit defects in the central processing of vision that are undetected by conventional perimetry. Movement of one finger in all parts of each temporal field may disclose no abnormality, but if movement is simultaneous in analogous parts of both temporal fields, the patient with hemispatial neglect from a parietal lobe lesion, especially on the right, may perceive only the one in the normal right hemifield.


Neurology_Adams

Neurology_Adams. A type of abnormality disclosed by visual field examination is concentric constriction. This may be a result of severe papilledema, in which case it is usually accompanied by an enlargement of the blind spot. A progressive constriction of the visual fields, at first unilateral and later bilateral, associated with pallor of the optic discs (optic atrophy), should suggest a chronic meningeal process involving the optic nerves (syphilis, cryptococcosis, sarcoidosis, lymphoma). Long-standing, untreated glaucoma and retinitis pigmentosa are other causes of concentric constriction. Marked constriction of the visual fields of unvarying degree, regardless of the distance at which the visual field is tested, is termed “tubular constriction”; it defies geometric principles and is a sign of hysteria. With organic disease, the constricted visual field enlarges as the distance between the patient and the testing screen increases.


Neurology_Adams

Neurology_Adams. It is hardly possible within the confines of this chapter to describe all the causes of opacification of the refractive media. Those with the most important medical or neurologic implications are briefly commented upon. Although changes in the refractive media do not involve neural tissue primarily, certain ones assume importance because they are associated with neurologic disease.


Neurology_Adams

Neurology_Adams. In the cornea, the most common abnormality that reduces vision is scarring caused by trauma and infection. Ulceration and subsequent fibrosis may occur following recurrent herpes simplex, herpes zoster, and trachomatous infections of the cornea, or with certain mucocutaneous-ocular syndromes (Stevens-Johnson, Reiter). Hypercalcemia secondary to sarcoidosis, hyperparathyroidism, and vitamin D intoxication or milk-alkali syndrome may give rise to precipitates of calcium phosphate and carbonate beneath the corneal epithelium, primarily in a plane corresponding to the interpalpebral fissure—so-called band keratopathy. Other causes of corneal opacity include chronic uveitis, interstitial keratitis, corneal edema, lattice corneal dystrophy (amyloid deposition), and long-standing glaucoma. Polysaccharides are deposited in the corneas in some of the mucopolysaccharidoses (see Chap. 37), and copper is deposited in the Descemet membrane in hepatolenticular degeneration (Kayser-Fleischer ring).


Neurology_Adams

Neurology_Adams. are deposited in the corneas in some of the mucopolysaccharidoses (see Chap. 37), and copper is deposited in the Descemet membrane in hepatolenticular degeneration (Kayser-Fleischer ring). Crystal deposits may be observed in multiple myeloma and cryoglobulinemia. The corneas are also diffusely clouded in certain lysosomal storage diseases (see Chap. 37). Arcus senilis occurring at an early age (because of hyperlipidemia), sometimes combined with yellow lipid deposits in the eyelids and periorbital skin (xanthelasma), serves as a marker of atheromatous vascular disease.


Neurology_Adams

Neurology_Adams. In the anterior chamber of the eye, a common problem is impediment to the outflow of aqueous fluid, associated with excavation of the optic disc and visual loss, that is, glaucoma. In more than 90 percent of cases (of the open-angle type), the cause of this syndrome is unknown and a genetic factor is suspected. The drainage channels in this type appear normal. In approximately 5 percent of cases, the angle between iris and the peripheral cornea is narrow and blocked when the pupil is dilated (angle-closure glaucoma). In the remaining cases, the condition is a result of some disease process that blocks outflow channels—inflammatory debris of uveitis, red blood cells from hemorrhage in the anterior chamber (hyphema), new formation of vessels and connective tissue on the surface of the iris (rubeosis iridis), a relatively infrequent complication of ocular ischemia secondary to diabetes mellitus, retinal vein occlusion, or carotid artery occlusion. The visual loss is gradual in open-angle


Neurology_Adams

Neurology_Adams. iridis), a relatively infrequent complication of ocular ischemia secondary to diabetes mellitus, retinal vein occlusion, or carotid artery occlusion. The visual loss is gradual in open-angle glaucoma and the eye looks normal, unlike the red, painful eye of angle-closure glaucoma that was described previously in reference to pharmacologic dilation of the pupil to facilitate fundoscopy.


Neurology_Adams

Neurology_Adams. Intraocular pressures that are persistently above 20 mm Hg may damage the optic nerve over time. This may be manifest first as an arcuate defect in the upper or lower nasal field or as a paracentral field defect, which, if untreated, may proceed to blindness. The classic finding in glaucoma is the Bjerrum field defect, consisting of an arcuate scotoma extending from the blind spot and sweeping around the macula to end in a horizontal line at the nasal equator. Other characteristic glaucomatous field patterns are winged extensions from the blind spot (Seidel scotoma) and a narrowing of the superior nasal quadrant that may progress to a horizontal edge, corresponding to the horizontal raphe of the retina (nasal step). The damage is at the optic nerve head, the optic disc appearing excavated, typically without pallor of the neuroretinal rim, thus distinguishing it from other optic neuropathies. Elongation of the optic cup in the vertical axis is typical. It is now appreciated that


Neurology_Adams

Neurology_Adams. typically without pallor of the neuroretinal rim, thus distinguishing it from other optic neuropathies. Elongation of the optic cup in the vertical axis is typical. It is now appreciated that elevated intraocular pressure is only a concurrent finding and a risk factor for glaucoma, but similar optic nerve damage with “cupping” may be seen in patients with near normal pressure. This represents a major revision of the previous view that pressure was the elemental cause of damage in glaucoma.


Neurology_Adams

Neurology_Adams. In the lens, cataract formation is a common abnormality characterized by clouding that usually develops slowly. The mundane “senile” cataract occurs because lens proteins denature and degrade over time. The “sugar cataract” of diabetes mellitus is the result of sustained high levels of blood glucose, which changes in the lens to sorbitol that causes a high osmotic gradient with swelling and disruption of the lens fibers. Galactosemia is a much rarer cause, but the mechanism of cataract formation is similar, that is, the accumulation of dulcitol in the lens. In hypoparathyroidism, lowering of the concentration of calcium in the aqueous humor is in some way responsible for the opacification of newly forming superficial lens fibers. Prolonged high doses of corticosteroids, as well as radiation therapy, induce lenticular opacities in some patients. Down syndrome and oculocerebrorenal syndrome (see Chap. 37), spinocerebellar ataxia with oligophrenia (see Chap. 38), and certain dermatologic


Neurology_Adams

Neurology_Adams. therapy, induce lenticular opacities in some patients. Down syndrome and oculocerebrorenal syndrome (see Chap. 37), spinocerebellar ataxia with oligophrenia (see Chap. 38), and certain dermatologic syndromes (atopic dermatitis, congenital ichthyosis, incontinentia pigmenti) are also accompanied by lenticular opacities. Myotonic dystrophy (see Chap. 45) and, rarely, Wilson disease (see Chap. 36) are associated with special types of cataract. Subluxation of the lens, the result of weakening of its zonular ligaments, occurs in syphilis, Marfan syndrome (upward displacement), and homocystinuria (downward displacement).


Neurology_Adams

Neurology_Adams. In the vitreous humor, hemorrhage may occur from rupture of a ciliary or retinal vessel. On ophthalmoscopic examination, the hemorrhage appears as a diffuse haziness of part or all of the vitreous, or takes the form of a sharply defined clot if it lies between the retina and the vitreous (termed preretinal or subhyaloid hemorrhage). The common cause is rupture of newly formed vessels of proliferative retinopathy in patients with diabetes mellitus, but there are many others including orbital or cranial trauma, rupture of an intracranial aneurysm or arteriovenous malformation with high intracranial pressure (Terson syndrome), valsalva maneuvers, retinal vein occlusion, sickle cell disease, age-related macular degeneration (ARMD), and retinal tears, in which the hemorrhage breaks through the internal limiting membrane of the retina. The most common vitreous opacities are benign “floaters” caused by the condensation of vitreous collagen fibers, which appear as darting gray flecks or


Neurology_Adams

Neurology_Adams. the internal limiting membrane of the retina. The most common vitreous opacities are benign “floaters” caused by the condensation of vitreous collagen fibers, which appear as darting gray flecks or threads with changes in the position of the eyes; they may be annoying or even alarming until the person stops looking for them.


Neurology_Adams

Neurology_Adams. A sudden burst of flashing lights associated with an increase in floaters may mark the onset of retinal detachment. Patients complaining of bright flashes and spots in vision should be examined with the indirect ophthalmoscope to rule out tears, holes, or detachments of the vitreous or retina. Another common occurrence with advancing age is shrinkage of the vitreous humor and retraction from the retina, causing persistent streaks of light, usually in the periphery of the visual field. These phosphenes, also known as Moore lightning streaks, had been thought to be quite benign, but they may at times indicate incipient retinal or vitreous tears or detachment, and their first appearance requires prompt evaluation by an ophthalmologist. They are most prominent on movement of the globe, on closure of the eyelids, at the moment of accommodation, with saccadic eye movements, and with sudden exposure to dark. The vitreous may also be infiltrated by lymphoma also occurring in the brain; biopsy


Neurology_Adams

Neurology_Adams. of the eyelids, at the moment of accommodation, with saccadic eye movements, and with sudden exposure to dark. The vitreous may also be infiltrated by lymphoma also occurring in the brain; biopsy by planar vitrectomy may be used to establish the diagnosis in those rare instances where the lymphoma is restricted to the eye.


Neurology_Adams

Neurology_Adams. The term uveitis refers to an infective or noninfective inflammatory disease that affects any of the uveal structures (iris, ciliary body, and choroid). The inflammation may be in the anterior part of the eye or in the posterior part, behind the iris and extending to the retina and choroid. Infective causes of posterior uveitis (choroidal) are toxoplasmal and cytomegalic inclusion disease, occurring mainly in patients with AIDS and other forms of reduced immune function. Noninfective autoimmune types are also common in the adult. Anterior uveitis is sometimes linked to ankylosing spondylitis and the human leukocyte antigen (HLA) B-27 marker, sarcoidosis, and recurrent meningitis (Vogt-Koyanagi-Harada disease); the posterior forms are associated with sarcoidosis, Behçet disease, and lymphoma. Retinal diseases, particularly ARMD and diabetic retinopathy, are another important cause of blindness and are discussed further on, under “Other Diseases of the Retina.”


Neurology_Adams

Neurology_Adams. Knowledge of certain anatomic and physiologic facts is required for an interpretation of the neurologic lesions that affect vision. Light entering the eye traverses the inner layers of the retina to reach its outer (posterior) layer, which contains two classes of photoreceptor cells: the flask-shaped cones and the slender rods. The photoreceptors rest on a single layer of pigmented epithelial cells, which form the outermost surface of the retina. The rods and cones and pigmentary epithelium receive their blood supply primarily from the capillaries of the choroid. The rods function in the perception of visual stimuli in subdued light (twilight or scotopic vision), and the cones are responsible for color discrimination and the perception of stimuli in bright light (photopic vision). Most of the cones are concentrated in the macular region, particularly in its central part, the fovea, and are responsible for the highest level of visual acuity. Traquair described the rapid fall-off of


Neurology_Adams

Neurology_Adams. of the cones are concentrated in the macular region, particularly in its central part, the fovea, and are responsible for the highest level of visual acuity. Traquair described the rapid fall-off of acuity as the distance from the fovea increases as “an island of vision in a sea of blindness.” Specialized pigment molecules in the rods and cones absorb light energy and transform it into electrical signals, which are transmitted to the bipolar cells of the retina and then, in turn, to the superficially (anteriorly) placed neurons, or ganglion cells (Fig. 12-3). In the fovea, ganglion cells and other inner retinal structures are displaced (they are not found there) so that photoreceptors can be very highly concentrated to maximize central spatial acuity.


Neurology_Adams

Neurology_Adams. The axons of the retinal ganglion cells follow an arcuate course across the inner surface of the retina. Being unmyelinated, they are not visible, although fluorescein retinography shows a trace of their outlines; an experienced examiner, using a bright light and deep green filter, can visualize them through direct ophthalmoscopy. The axons of ganglion cells are collected in the optic discs and then travel posteriorly to form the optic nerves, optic chiasm, and optic tracts, finally synapsing in the lateral geniculate nuclei, the superior colliculi, the midbrain pretectum and the suprachiasmatic nucleus of the hypothalamus (see Figs. 12-2 and 12-3). The fibers derived from macular cells form a discrete group (the papillomacular bundle) that arrive at the temporal side of the disc and then assume a more central position within the nerve. These fibers are of smaller caliber than the peripheral optic nerve fibers and appear to be especially sensitive to toxic and metabolic injury. Damage


Neurology_Adams

Neurology_Adams. assume a more central position within the nerve. These fibers are of smaller caliber than the peripheral optic nerve fibers and appear to be especially sensitive to toxic and metabolic injury. Damage to the papillomacular bundle produces the “cecocentral” scotoma (extending from fixation to the blind spot).


Neurology_Adams

Neurology_Adams. The absence of receptive elements in the optic disc accounts for the normal blind spot. The normal optic disc varies in color, being paler in infants and in blond individuals. The ganglion cell axons normally acquire their myelin sheaths after penetration of the lamina cribrosa, but they sometimes do so in their intraretinal course, as they approach the disc. These myelinated fibers adjacent to the disc appear as white patches with fine-feathered edges and are a normal variant, not to be confused with optic disc edema or retinal ischemia. If there is a lesion in one optic nerve, a light stimulus to the affected eye will have no effect on the pupil of either eye, although the ipsilateral pupil will still constrict consensually, that is, in response to a light stimulus from the normal eye. This phenomenon is termed a relative afferent pupillary defect (the Marcus Gunn pupil).


Neurology_Adams

Neurology_Adams. In the optic chiasm, the fibers derived from the nasal half of each retina decussate and continue in the optic tract with the uncrossed temporal fibers of the other eye (Figs. 12-2 and 12-4). Thus, interruption of the left optic tract causes a right hemianopic defect in each eye, that is, a homonymous (left nasal and right temporal) field defect (see Fig. 12-2D). In partial tract lesions, the visual defects in the two eyes may not be congruent, as the tract fibers are not evenly admixed. Lesions at the junction of the optic nerve and chiasm, generally compressive in nature, may cause a small contralateral superotemporal quadrantic defect in addition to the expected central scotoma in the ipsilateral eye (“junctional scotoma,” Fig. 12-2B). It had been thought for many decades to result from compression of Wilbrand knee, a bundle of fibers that turn back into the contralateral optic nerve before crossing in the chiasm, but it has since been related by Horton that the very existence of


Neurology_Adams

Neurology_Adams. compression of Wilbrand knee, a bundle of fibers that turn back into the contralateral optic nerve before crossing in the chiasm, but it has since been related by Horton that the very existence of the bundle is merely an artifact of long-term monocular enucleation.


Neurology_Adams

Neurology_Adams. The optic chiasm lies just above the pituitary gland and also forms part of the anterior wall of the third ventricle; hence, the crossing fibers may be compressed from below by a pituitary tumor, a meningioma of the tuberculum sellae, or an aneurysm, and from above by a dilated third ventricle or craniopharyngioma. The resulting field defect is bitemporal (“bitemporal hemianopia”; Fig. 12-2C). In albinism, there is an abnormality of chiasmatic decussation, in which a majority of the fibers cross to the other side because of a defect in melanin signaling that normally contributes to patterning of the chiasm.


Neurology_Adams

Neurology_Adams. From the retina, there is a point-to-point projection to the lateral geniculate nucleus and from there, to the calcarine cortex of the occipital lobe. For purposes of description of the visual fields, each retina and macula are divided into a temporal and nasal half by a vertical line passing through the fovea. A horizontal line represented roughly by the junction of the superior and inferior retinal vascular arcades also passes through the fovea and divides each half of the retina and macula into upper and lower quadrants. Visual field defects are always described from the patient’s view (nasal, temporal, superior, inferior) rather than of the retinal defect or the examiner’s perspective. The retinal image of an object in the visual field is inverted and reversed from right to left, like the image on the film of a camera. Thus the left visual field of each eye is represented in the opposite half of each retina, with the upper part of the field represented in the lower part of the


Neurology_Adams

Neurology_Adams. the image on the film of a camera. Thus the left visual field of each eye is represented in the opposite half of each retina, with the upper part of the field represented in the lower part of the retina (Figs. 12-2 and 12-4). Figure 12-5 illustrates the retinal projections to the geniculate nuclei and occipital cortex.


Neurology_Adams

Neurology_Adams. Approximately 80 percent of the fibers of the optic tract terminate in the lateral geniculate nucleus of the thalamus and synapse with the six laminae of its neurons. Three of these laminae (1, 4, 6) receive crossed (nasal) fibers from the contralateral eye, and three (2, 3, 5) receive uncrossed (temporal) fibers from the ipsilateral eye. Selective occlusion of either component of the dual blood supply to the lateral geniculate, consisting of the anterior and posterior choroidal arteries, is infrequent but when it does occur, produces a characteristic “multiple sectoral field defect.” Occlusion of the anterior choroidal artery produces a contralateral quadruple sectoranopia, meaning homonymous sectoral defects in the upper and lower quadrants of both eyes. Occlusion of the posterior (lateral) choroidal artery produces a contralateral homonymous horizontal sectoranopias.


Neurology_Adams

Neurology_Adams. The geniculate cells project via the optic radiations to the visual (striate) cortex of the occipital lobe, also called area 17 (Brodmann classification) or V1 (Figs. 12-4 and 12-5). In their course through the temporal lobes, the fibers from the lower and upper quadrants of each retina diverge. The lower ones arch around the anterior pole of the temporal horn of the lateral ventricle before turning posteriorly (forming Meyer’s loop), and their disruption causes a contralateral superior quadrant field deficit. The upper ones follow a more direct path through the white matter of the uppermost part of the temporal lobe (Fig. 12-4), and probably of the adjacent interior parietal lobe; their disruption causes a contralateral inferior field deficit. Both groups of fibers merge posteriorly at the internal sagittal stratum (see Fig. 12-2E and F).


Neurology_Adams

Neurology_Adams. It is in Brodmann area 17, embedded in the medial lip of the occipital pole, that cortical processing of the retinogeniculate projections occurs. The receptive neurons are arranged in columns, some of which are activated by edges and forms and others by moving stimuli or by color. The neurons for each eye are grouped together and have concentric, center-surround receptive fields. The seminal studies of Hubel and Wiesel have elucidated much of this visual cortical anatomy and physiology and their papers, for which they were awarded the Nobel Prize, should be consulted for a fuller appreciation of the organization of the visual cortex. The deep neurons of area 17 project to the secondary and tertiary visual areas of the occipitotemporal cortex of the same and opposite cerebral hemispheres and also to other multisensory parietal and temporal cortices. These complex extrastriate connections are still being elucidated.


Neurology_Adams

Neurology_Adams. Portions of the visual systems are specialized for the perception of motion, color, stereopsis, contour, and depth perception. As Ungerleider and Mishkin proposed, the flow of secondary visual processing can be conceptually divided into a dorsal stream, which carries predominantly spatial information to the parietal lobe (“the where”) and a ventral stream, which carries shape and color information to the temporal lobe (“the what”) as proposed by Goodale and Milner in 1992 and further articulated by Levine and colleagues.


Neurology_Adams

Neurology_Adams. The normal development of the connections described previously requires that the visual system be activated through several critical periods of development. The early deprivation of vision in one eye causes a failure of development of the geniculate and cortical receptive fields of that eye. Moreover, in this circumstance the cortical receptive fields of the seeing eye become abnormally large and usurps the monocular dominance columns of the blind eye (Hubel and Wiesel). In children with a congenital cataract, if the opacity is removed after a critical period of development, the eye will remain amblyopic. A severe strabismus in early life, especially an esotropia, will have the same effect (amblyopia ex anopsia).


Neurology_Adams

Neurology_Adams. The vascular supply of the eye is through the ophthalmic branch of the internal carotid artery that supplies the retina, posterior (uveal) coats of the eye, and optic nerve head. This artery gives origin to the posterior ciliary arteries; the latter form a rich circumferential plexus of vessels (arterial circle of Zinn-Haller) located deep to the lamina cribrosa. The lamina cribrosa is a sieve-like scleral (dural) structure through which the axons of the central and nasal part of the disc run. This arterial circle supplies the optic disc and adjacent part of the distal optic nerve, the choroid, and the ciliary body; it anastomoses with the pial arterial plexus that surrounds the optic nerve. The other major branch of the ophthalmic artery is the central retinal artery. It issues from the optic disc, where it divides into four branches that supply the inner retinal layers; it is these vessels and their branches that are visible by ophthalmoscopy. A short distance from the disc, these


Neurology_Adams

Neurology_Adams. optic disc, where it divides into four branches that supply the inner retinal layers; it is these vessels and their branches that are visible by ophthalmoscopy. A short distance from the disc, these vessels lose their internal elastic lamina and the media (muscularis) becomes thin; they are properly classed as arterioles. The inner layers of the retina, including the ganglion and bipolar cells, receive their blood supply from these arterioles and their capillaries, whereas the deeper photoreceptor elements and the fovea are nourished by the underlying choroidal vascular bed, by diffusion through the retinal pigmented cells and the semipermeable Bruch membrane upon which they rest. In up to a third of the population, a small cilioretinal artery may arise from either the choroidal circulation or from the circle of Zinn-Haller and supply the macula. In the case of a central retinal artery occlusion, the presence of this cilioretinal artery leads to the preservation of central acuity.


Neurology_Adams

Abnormalities of the Retina

Neurology_Adams. Abnormalities of the Retina


Neurology_Adams

Neurology_Adams. As indicated previously, the thin (100to 350-mm) retinal sheet and the optic nerve head are exteriorized parts of the central nervous system and the only part of the nervous system that can be inspected directly. In cases of visual loss it is important during funduscopic examination to carefully inspect the macular zone (which is located 3 to 4 mm lateral to the optic disc and provides central visual acuity). There are variations in the appearance of the normal macula and optic disc, and these may prove difficult to distinguish from disease. A normal macula may be called abnormal because of a slight aberration of the retinal pigment epithelium or a few drusen. With experience, the examiner can visualize the unmyelinated nerve-fiber layer of the retina by using bright-green (red-free) illumination. This is most often helpful in detecting demyelinating, toxic, or hereditary lesions of the optic nerve, which produce a loss of discrete bundles of axons as they converge to the disc.


Neurology_Adams

Neurology_Adams. In evaluating the retinal vessels, one must remember that these are arterioles and not arteries. Since the walls of retinal arterioles are transparent, what is observed with the ophthalmoscope is a column of blood within them. The central light streak of normal arterioles is thought to represent the reflection of light as it strikes the interface of the column of blood and the concave vascular wall. In arteriolosclerosis (usually coexistent with hypertension), the lumina of the vessels are segmentally narrowed because of fibrous tissue replacement of the media and thickening of the basement membrane. Straightening of the arterioles and venous compression by arterioles (“A-V nicking”) are other signs of hypertension and arteriolosclerosis. In this circumstance the vein is compressed by the thickened arteriole within the adventitial envelope shared by both vessels at the site of crossing. Progressive arteriolar disease, to the point of occlusion of the lumen, results in a narrow, white


Neurology_Adams

Neurology_Adams. thickened arteriole within the adventitial envelope shared by both vessels at the site of crossing. Progressive arteriolar disease, to the point of occlusion of the lumen, results in a narrow, white (“silver-wire”) vessel with no visible blood column. This change is associated most often with severe hypertension but may follow other types of occlusion of the central retinal artery or its branches (see descriptions and retinal illustrations further on). Sheathing of the venules, probably representing focal leakage of cells from the vessels, can accompany inflammatory neuropathies, including idiopathic optic neuritis. Arterial and venule sheathing are also seen in leukemia, sarcoid, Behçet disease, and other forms of vasculitis.


Neurology_Adams

Neurology_Adams. In malignant, or accelerated, hypertension, there are, in addition to swelling of the optic nerve head and the retinal arteriolar changes noted previously, a number of extravascular lesions: the so-called soft exudates or cotton-wool patches, sharply marginated and glistening “hard” exudates, and retinal hemorrhages (Fig. 12-6). In many patients who show these retinal changes, analogous lesions are found in the brain (necrotizing arteriolitis and microinfarcts) and underlie hypertensive encephalopathy.


Neurology_Adams

Neurology_Adams. Microaneurysms of retinal vessels appear as small, discrete red dots and are located in largest number in the paracentral region. They are most often a sign of diabetes mellitus, sometimes appearing before the usual clinical manifestations of that disease. The use of the red-free (green) light on the ophthalmoscope helps to pick out microaneurysms from the background. Microscopically, the aneurysms take the form of small (20to 90-mm) saccular outpouchings from the walls of capillaries, venules, or arterioles. The vessels of origin of the aneurysms are invariably abnormal, being either acellular branches of occluded vessels or themselves occluded by fat or fibrin.


Neurology_Adams

Neurology_Adams. The ophthalmoscopic appearance of retinal hemorrhage is determined by the structure of the particular tissue in which it occurs. In the superficial layer of the retina, they are linear or flame-shaped (“splinter” hemorrhages) because of their confinement by the horizontally coursing nerve fibers in that layer. These hemorrhages usually overlie and obscure the retinal vessels. Round or oval (“dot-and-blot”) hemorrhages lie behind the vessels, in the outer plexiform layer of the retina (synaptic layer between bipolar cells and nuclei of rods and cones—Fig. 12-3); in this layer, blood accumulates in the form of a cylinder between vertically oriented nerve fibers and appears round or oval when viewed end-on with the ophthalmoscope. Rupture of arterioles on the inner surface of the retina—as occurs with ruptured intracranial saccular aneurysms, arteriovenous malformations, and other conditions causing sudden severe elevation of intracranial pressure—permits the accumulation of a sharply


Neurology_Adams

Neurology_Adams. occurs with ruptured intracranial saccular aneurysms, arteriovenous malformations, and other conditions causing sudden severe elevation of intracranial pressure—permits the accumulation of a sharply outlined lake of blood between the internal limiting membrane of the retina and the vitreous or hyaloid membrane (the condensed gel at the periphery of the vitreous body); this is the subhyaloid or preretinal hemorrhage, termed Terson syndrome (Fig. 12-7). Either the small superficial or deep retinal hemorrhage may show a central or eccentric pale (Roth) spot, which is caused by an accumulation of white blood cells, fibrin, histiocytes, or amorphous material between the vessel and the hemorrhage. This lesion is said to be characteristic of bacterial endocarditis, but it is also seen in leukemia and occasionally in embolic retinopathy caused by carotid disease.


Neurology_Adams

Neurology_Adams. Cotton-wool patches, or soft exudates, refer to areas of inner retinal opacification resulting from ischemia due to occlusion of precapillary arterioles. These patches, even large ones, rarely cause serious disturbances of vision unless they involve the macula. They are composed of clusters of ovoid structures called cytoid bodies, representing the terminal swellings of interrupted axons. Hard exudates appear as punctate white or yellow bodies; they lie in the outer plexiform layer, behind the retinal vessels, like the punctate hemorrhages. If present in the macular region, they are arranged in lines radiating toward the fovea (macular). Hard exudates consist of lipid and other serum precipitants as a result of abnormal vascular permeability of a type that is not completely understood. They are observed most often in cases of diabetes mellitus and chronic hypertension.


Neurology_Adams

Neurology_Adams. Drusen in the retina (colloid bodies) appear ophthalmoscopically as pale yellow spots and are difficult to distinguish from hard exudates except when they occur alone; as a rule, hard exudates are accompanied by other funduscopic abnormalities. Although retinal drusen may be a benign finding, in many cases they reflect an ARMD and their accumulation in the macula eventually leads to significant visual loss. The source of retinal drusen is uncertain, but they may result from chronic inflammation generated by degeneration of the retinal pigment epithelium. Hyaline bodies, located on or near the optic disc, are also referred to as drusen but must be distinguished from those occurring peripherally. In contrast to peripheral retinal drusen, drusen of the optic discs are probably mineralized residues of dead axons and can be seen on CT in some cases. Their main significance for neurologists is that drusen that are buried under the disc (“buried drusen”) are often associated with anomalous


Neurology_Adams

Neurology_Adams. of dead axons and can be seen on CT in some cases. Their main significance for neurologists is that drusen that are buried under the disc (“buried drusen”) are often associated with anomalous elevation of the disc that can be mistaken for papilledema (see further on).


Neurology_Adams

Neurology_Adams. The periphery of the retina may harbor a hemangioblastoma, which may appear during adolescence, before the more characteristic cerebellar lesion. A large retinal artery may be seen leading to it and there may be a large draining vein. Occasionally, retinal examination discloses the presence of a vascular malformation that may coexist with a malformation of the optic nerve and basilar portions of the brain. Ischemic Lesions of the Retina


Neurology_Adams

Neurology_Adams. Transient monocular blindness Transient ischemic attacks of visual loss involving all or part of the field of vision of one eye are referred to as amaurosis fugax or transient monocular blindness (TMB). They are common manifestations of atherosclerotic carotid stenosis but have other causes. An altitudinal horizontal border, or “shade,” is often, but not invariably, an aspect of the visual loss. The shade may rise or fall at the onset or cessation of the spell and occasionally remains throughout the episode. Fortuitous inspection of the retina during an attack may show segments of arteries that are filled with white material that migrate distally over many minutes. There can be stagnation of arterial and venous blood flow, which returns within seconds or minutes as vision is restored (Fisher). One interpretation of these observations is that an embolus to the central retinal artery and has broken up and moved distally. Fisher went on to discredit the theory of the time that transient


Neurology_Adams

Neurology_Adams. One interpretation of these observations is that an embolus to the central retinal artery and has broken up and moved distally. Fisher went on to discredit the theory of the time that transient monocular blindness was due to vasospasm of the retinal arteries.


Neurology_Adams

Neurology_Adams. Many attacks may precede infarction of a cerebral hemisphere, or they may abate without adverse consequence. In one series of 80 patients followed by Marshall and Meadows for 4 years, in an era prior to modern treatment of atherosclerosis, 16 percent developed permanent unilateral blindness, a completed hemispheric stroke, or both. Chapter 33 discusses this subject further.


Neurology_Adams

Neurology_Adams. Occlusion of the internal carotid artery usually causes no disturbance of vision, provided that there are adequate anastomotic branches from the external carotid artery or other sources to the ophthalmic artery. Occasionally, occlusion of the proximal internal carotid artery is marked by an episode of transient monocular blindness on the same side, just as a hemispheric transient ischemic attack may indicate recent acute carotid occlusion. Chronic carotid occlusion with inadequate collateralization is associated with an ischemic oculopathy, which may predominantly affect the anterior or posterior segment or both (see Young and Appen). In this case, insufficient circulation to the anterior segment of the globe is manifest by scleral vascular congestion, cloudiness of the cornea, anterior chamber flare, and low intraocular pressure, or sometimes high intraocular pressure if neovascularization of the iris (rubeosis iridis) occurs and compromises the outflow of aqueous humor. Ischemia of


Neurology_Adams

Neurology_Adams. flare, and low intraocular pressure, or sometimes high intraocular pressure if neovascularization of the iris (rubeosis iridis) occurs and compromises the outflow of aqueous humor. Ischemia of the posterior segment of the eye is manifest by circulatory changes in the optic nerve or by venous stasis. Light-induced amaurosis, in which periods of blindness are precipitated by exposure to bright light, is a characteristic symptom. Other signs of carotid disease may be present, for example, a local bruit over the carotid bifurcation.


Neurology_Adams

Neurology_Adams. Central or branch retinal artery occlusion Most often, ischemia of the retina can be traced to occlusion of the central retinal artery or its branches by thrombi or emboli—central or branch retinal artery occlusion (CRAO or BRAO). Occlusion is attended by sudden painless blindness. The retina becomes opaque and has a gray-yellow appearance; the arterioles are narrowed, with segmentation of columns of blood. A “cherry-red spot” appears in the fovea, where the retina is thinnest and the intact underlying choroidal circulation is visible (Fig. 12-8).


Neurology_Adams

Neurology_Adams. With occlusions of smaller branches of the central retinal artery by emboli, one may be able to see the occluding material. Most frequently observed are Hollenhorst plaques—glistening, white-yellow atheromatous particles (Fig. 12-9) seen in 40 of 70 cases of retinal embolism in the series of Arruga and Sanders. These plaques can also be an asymptomatic manifestation of carotid or aortic atherosclerosis. Intraluminal particles may alternatively have the appearance of white calcium from aortic or mitral valves or atheroma of the great vessels. Red or white fibrin-platelet emboli may emanate from the heart, its valves, or other sources. Emboli to retinal artery branches may be difficult to see without fluorescein retinography; furthermore, most of these emboli soon disappear. Central and branch retinal artery occlusions also occur as a consequence of hypercoaguable states, including anti-phospholipid antibody syndrome. Giant cell arteritis is another important cause; patients who are in


Neurology_Adams

Neurology_Adams. retinal artery occlusions also occur as a consequence of hypercoaguable states, including anti-phospholipid antibody syndrome. Giant cell arteritis is another important cause; patients who are in their fifties or older should be screened for this condition.


Neurology_Adams

Neurology_Adams. It has become routine in some centers to treat acute central retinal artery occlusion in an urgent manner with a number of methods in the hope that the embolus or thrombus will be propelled into more distal vessels. These treatments are generally aimed at lowering intraocular pressure (acetazolamide, inhalation of carbon dioxide; paracentesis of the anterior chamber, ballottement), to dilate the vessels, and reestablish flow. We can only offer the impression that these procedures have generally often not been successful. Some case series have suggested that local thrombolysis with intraarterial agents may be useful, although a multicenter controlled trial of thrombolysis (Eagle Study cited under Schumacher and colleagues) was halted early because of concerns about safety.


Neurology_Adams

Neurology_Adams. Retinal venous occlusion Because the central retinal artery and vein share a common adventitial sheath, atheromatous plaques in the artery can provoke thrombosis of the retinal vein. This results in a spectacular display of retinal lesions that differs from the picture of central retinal artery occlusion. The veins are engorged and tortuous, and there are multiple diffuse “dot-and-blot” and streaky linear retinal hemorrhages (Fig. 12-10). Retinal vein thrombosis is observed most frequently with diabetes mellitus, hypertension, and leukemia; less frequently with sickle cell disease; and rarely with multiple myeloma, and Waldenstrom macroglobulinemia in relation to the hyperviscosity that these two diseases cause. Sometimes, no associated systemic disease can be identified, in which case the possibility of an orbital mass (e.g., optic nerve glioma) should be considered. In retinal vein thrombosis, visual loss is variable and there may be recovery of useful vision. In cases where macular


Neurology_Adams

Neurology_Adams. possibility of an orbital mass (e.g., optic nerve glioma) should be considered. In retinal vein thrombosis, visual loss is variable and there may be recovery of useful vision. In cases where macular edema ensues, recovery may be enhanced by laser photocoagulation.


Neurology_Adams

Neurology_Adams. Benign retinal vasospasm and migraine In addition to the typical ischemic cause of this syndrome, transitory retinal ischemia is observed occasionally as a manifestation of migraine. Rarely, benign vasospasm of the central retinal artery may be implicated as a cause of recurrent transient monocular blindness, in which case the episodes may cease with the introduction of a calcium channel blocker, as reported by Winterkorn and colleagues. Other Diseases of the Retina Aside from vascular lesions, tears and detachments of the retina may impair vision acutely. The most common form of detachment is a separation of the pigment epithelium layer from the sensory retina with fluid accumulation through a tear or hole in the retina. In so-called traction detachment—observed in cases of premature birth or proliferative retinopathy secondary to diabetes or other vascular disease—contracting fibrous tissue pulls the retina from the choroid.


Neurology_Adams

Neurology_Adams. Serous retinopathy, a cause of monocular visual disturbance in young or middle-aged males, may be associated with the use of corticosteroids. The entire perimacular zone is elevated by edema fluid. The condition may arise acutely or slowly. Metamorphopsia (distortion of vision) in one eye is a common presentation, but acuity is not much impaired. The optic disc remains normal. The retinal change (leakage of vascular fluid into the subretinal space) causes a loss of visualization of the detail of the choroid and is demonstrated by fluorescein angiography or by optical coherence tomography (OCT). The condition tends to resolve over several months and can be treated by laser to seal the sites of leakage.


Neurology_Adams

Neurology_Adams. Chorioretinitis, the result of an infectious process, may cause difficulty in diagnosis. Cat Scratch disease, caused by Bartonella henselae, is a consideration. In many patients the initial diagnosis had been retrobulbar neuritis. One cannot depend upon the appearance of a macular star (see earlier under “cotton wool patches”) for diagnosis.


Neurology_Adams

Neurology_Adams. A large number of patients with HIV-AIDS develop retinal lesions of various types. Infarcts of the nerve-fiber layer (cotton-wool patches), hemorrhages, and perivascular sheathing are the usual findings. Toxoplasmosis is the most common infective lesion, followed in frequency by cytomegalovirus (CMV), but histoplasmosis, Pneumocystis carinii, herpes zoster, syphilis, and tuberculosis are well documented. CMV may cause a particularly severe necrotizing retinitis and permanent impairment of vision. Both the retina and choroid may be involved by these diseases, in which case the ophthalmoscopic picture is characteristic, showing the destruction of the “punched-out” lesions that exposes the whitish sclera, and deposits of black pigment. The choroid may also be the site of viral and noninfective inflammatory reactions, often in association with painful recurrent iridocyclitis and lacrimal inflammation.


Neurology_Adams

Neurology_Adams. Degenerations of the retina are important causes of chronic progressive visual loss. The retinal degenerations assume several forms and can be associated with progressive conditions of the brain or other organs. The most frequent degeneration in youth and middle age is retinitis pigmentosa, a hereditary disease of the outer photoreceptor layer and subjacent pigment epithelium. The retina is thin, and there are fine deposits of black pigment in the shape of bone corpuscles, more in the periphery; later the optic discs become atrophic (described as “waxy pallor”). The disorder is marked by constriction of the visual fields with relative sparing of central vision (“gun-barrel” vision), metamorphopsia (distorted vision), delayed recovery from glare, and nyctalopia (reduced twilight vision). The causes of retinitis pigmentosa and related retinal degenerations are diverse, linked to deficits in more than 75 different genes. In one form of isolated retinitis pigmentosa, which follows an


Neurology_Adams

Neurology_Adams. The causes of retinitis pigmentosa and related retinal degenerations are diverse, linked to deficits in more than 75 different genes. In one form of isolated retinitis pigmentosa, which follows an autosomal dominant pattern of inheritance, the gene for rhodopsin (a combination of vitamin A and the rod-cell protein opsin) produces a defective opsin, resulting in a diminution of rhodopsin, diminished response to light, and eventual degeneration of the rod cells (Dryja et al). Retinitis pigmentosa is associated with the


Neurology_Adams

Neurology_Adams. Laurence-Moon-Biedl syndrome, with certain mitochondrial diseases (Kearns-Sayre syndrome, Chap. 37), and with a number of degenerative and metabolic diseases (e.g., Refsum disease) of the nervous system. Another early life hereditary retinal degeneration, characterized by massive central retinal lesions, is the autosomal recessive Stargardt form of juvenile tapetoretinal degeneration. Like retinitis pigmentosa, Stargardt disease may be accompanied by progressive spastic paraparesis or ataxia. Nonpigmentary retinal degeneration is a feature of a number of rare syndromes and diseases, such as neuronal ceroid lipofuscinosis, Bassen-Kornzweig disease, Batten-Mayou disease, and others (see Chap. 36).


Neurology_Adams

Neurology_Adams. Toxic effects of medications are an important cause of retinal damage. Phenothiazine derivatives, less often used in practice than they had been, may conjugate with the melanin of the pigment layer, resulting in degeneration of the outer layers of the retina and a characteristic “bull’s-eye retinopathy” observed by fluorescein angiography. If these drugs are administered in high dosages for protracted periods, the patient should be tested for defects in visual fields and color vision. Among drugs used to treat neurologic disease, the antiepileptic drug vigabatrin is notable for causing retinal degeneration and a concentric restriction of the visual fields in almost half of exposed patients. Elevated levels of gamma-aminobutyric acid (GABA) in the retina are presumably the cause of toxicity. High-dose tamoxifen has caused toxicity in the retina, characterized by the deposition of refractile opacities and in more severe cases, by macular edema.


Neurology_Adams

Neurology_Adams. A cancer-associated retinopathy (CAR) has been described in patients with small-cell lung cancer and other tumors as a paraneoplastic illness (see Chap. 30). The typical presentation is of positive visual phenomenon and rapid bilateral visual loss. Antibodies against the recoverin protein, which modulates rhodopsin kinase, have been demonstrated in the serum of affected patients (Grunwald et al; Kornguth et al; Jacobson et al). A melanoma-associated retinopathy (MAR) that produces night blindness and affects primarily rods has also been described. These paraneoplastic processes are further described in Chap. 30.


Neurology_Adams

Neurology_Adams. Certain lysosomal diseases of infancy and early childhood are characterized by an abnormal accumulation of undegraded proteins, polysaccharides, and lipids in cerebral neurons, as well as in the macula and other parts of the retina (hence the terms storage diseases and cerebromacular degenerations). Corneal clouding, cherry-red spot and graying of the retina, and later optic atrophy are the observed ocular abnormalities. Chapter 36 discusses these diseases.


Neurology_Adams

Neurology_Adams. In some of these retinal diseases, minimal changes in the pigment epithelium or other layers of the retina may not be readily detected by ophthalmoscopy. A test to expose such subtle retinal changes is to estimate the time required for recovery of visual acuity following light stimulation (macular photostress test). The test is conducted by shining a strong light through the pupil of an affected eye for 10 s and measuring the time necessary for the acuity to return to the pretest level (normally 50 s or less). With macular lesions, recovery time is prolonged, but with lesions of the optic nerve, it is not affected. As described earlier, this phenomenon may also be observed in the eye on the side of a carotid occlusion, which in essence causes an ischemic retinopathy. Retinal diseases reduce or abolish the electrical activity generated by the outer layers of the retina, and this can be measured by the electroretinogram (ERG). Fluorescein retinography and various new imaging tests are


Neurology_Adams

Neurology_Adams. or abolish the electrical activity generated by the outer layers of the retina, and this can be measured by the electroretinogram (ERG). Fluorescein retinography and various new imaging tests are now essential for proper diagnosis of retinal disease. OCT uses reflected light to construct a high-resolution two-dimensional image of the retinal layers; it is able to demonstrate with remarkable resolution retinal edema, tears, macular holes, and the thinning of the retinal nerve-fiber layer that follows optic neuropathy.


Neurology_Adams

Neurology_Adams. Age-related macular degeneration This is a frequent cause of visual loss in the elderly. As ARMD begins to disturb vision, the straight lines on the Amsler grid are observed by the patient to be distorted. Over time, central vision gradually diminishes, impairing reading, but these patients can navigate because of retained peripheral vision. Examination discloses a central scotoma with pigmentary changes in the region around the macula. The two most common types of macular degeneration are an atrophic “dry” type, which is a true pigmentary degeneration associated with retinal drusen, of unknown cause but with a genetic component, and an exudative “wet” type, which is the result of choroidal neovascularization that results in secondary macular damage. The wet form is amenable to laser treatment and injection into the orbit of ranibizumab or similar antiangiogenic monoclonal antibodies against vascular endothelial growth factor. Progression of the dry form may be slightly reduced by the


Neurology_Adams

Neurology_Adams. and injection into the orbit of ranibizumab or similar antiangiogenic monoclonal antibodies against vascular endothelial growth factor. Progression of the dry form may be slightly reduced by the use of antioxidants and zinc. The pathophysiology and treatment of ARMD have been reviewed by DeJong.


Neurology_Adams

Neurology_Adams. Diabetic retinopathy Although not strictly speaking a problem taken up by neurologists, this is such an important cause of reduced vision and blindness that the basic facts should be known to all physicians. The earliest changes are of microaneurysms, and tiny intraretinal hemorrhages; these are present in almost all diabetics who have had type 1 disease for more than 20 years. Cotton-wool spots and small hemorrhages appear as the retina becomes ischemic. Subsequently, there is a more threatening proliferative retinopathy that consists of the formation of new blood vessels, and consequent leakage of proteins and blood. The proliferative feature occurs in half of type 1 diabetics, and 10 percent of those who have had type 2 disease for 15 to 20 years. The new vessels can grow into the vitreous, and hemorrhages from them may cause traction on the retina, which results in detachment. Visual loss may also be the result of macular edema. Reabsorption of the edema leads to the deposition of


Neurology_Adams

Neurology_Adams. and hemorrhages from them may cause traction on the retina, which results in detachment. Visual loss may also be the result of macular edema. Reabsorption of the edema leads to the deposition of lipid “hard exudates.” The maintenance of glucose control reduces the frequency and severity of retinopathy but does not prevent it. Locally elevated levels of vascular endothelial growth factor have been shown to be involved in the pathophysiology of diabetic retinal neovascularization, and recent studies show that intravitreal injections of the antivascular endothelial growth factor (anti-VEGF) antibody, bevacizumab, can improve neovascular leakage, at least in the short term. The review of the subject by Antonetti and colleagues is recommended.


Neurology_Adams

Neurology_Adams. Of the various abnormalities of the optic disc, papilledema has the greatest neurologic implication, for it signifies the presence of increased intracranial pressure. The term papilledema has come to mean disc swelling due to raised intracranial pressure although there are other causes of a similar funduscopic appearance. An ophthalmoscopic appearance identical to that of papilledema can be produced, for example, by infarction of the optic nerve head (as with anterior ischemic optic neuropathy) and other conditions affecting the intraorbital portion of the optic nerve (especially inflammatory or infiltrative conditions). Certain clinical and funduscopic findings, listed in Table 12-2 and described in the following text, assist in distinguishing between these processes, although all share the basic feature of conspicuous optic disc swelling.


Neurology_Adams

Neurology_Adams. In its mildest form, papilledema appears as slight elevation of the disc and blurring of the disc margins, especially of the superior and inferior aspects, and a mild fullness of the veins in the disc. Subtle disc elevation is also indicated by a loss of definition of the vessels overlying the disc as they approach the disc margin from the periphery; this appearance is produced by edema in the adjacent retina. Because many normal individuals, especially those with hypermetropia, have ill-defined disc margins, the early stage of papilledema may be difficult to detect (Fig. 12-11). Pulsations of the retinal veins, best seen where the veins turn to enter the disc, will have disappeared by the time intracranial pressure is raised, but this finding is not specific, as venous pulsations are not present in a proportion of normal individuals in the seated position. On the other hand, the presence of spontaneous venous pulsations is usually a reliable indicator of an intracranial pressure


Neurology_Adams

Neurology_Adams. not present in a proportion of normal individuals in the seated position. On the other hand, the presence of spontaneous venous pulsations is usually a reliable indicator of an intracranial pressure below 200 mm H2O, and thus argue against true papilledema from elevated intracranial pressure (Levin). Fluorescein angiography, red-free fundus photos (which highlight the retinal nerve fibers), and ocular coherence tomography are helpful in detecting early edema of the optic discs.


Neurology_Adams

Neurology_Adams. More severe degrees of papilledema appear as further elevation, or “mushrooming” of the entire disc and surrounding retina. There is obscuration of vessels at the disc margins and, in some instances, peripapillary hemorrhages (Fig. 12-12). Advanced papilledema is almost always bilateral although it may asymmetric. In contrast, purely unilateral edema of the optic disc suggests an optic nerve sheath meningioma or other tumor involving the optic nerve, although it will sometimes be observed an early stage of increased intracranial pressure. As papilledema becomes chronic, elevation of the disc margin becomes less prominent and the optic nerve head develops pallor, representing a dropout of nerve fibers (atrophy) (Fig. 12-13). Varying degrees of secondary optic atrophy occur in the wake of papilledema that has persisted for more than several days or weeks, ultimately leaving the disc pale and gliotic.


Neurology_Adams

Neurology_Adams. Acute papilledema, while it may enlarge the blind spot slightly, usually does not have a great affect upon visual acuity (except transiently during spontaneous waves of increased intracranial pressure). Therefore, acute optic disc swelling in a patient with severely reduced vision should not be attributed to papilledema; instead, intraorbital optic neuritis (papillitis) or infarction of the nerve head (ischemic optic neuropathy) is more likely explanations. In rare cases of pseudotumor cerebri, visual loss may be unexpectedly abrupt, appearing in a day or less. This seems to happen most often in patients with constitutionally small optic nerves, no optic cup of the nerve head and, presumably, a small aperture of the lamina cribrosa. Such explosive visual loss in pseudotumor cerebri may respond to urgent optic nerve fenestration, but this approach is controversial, as discussed in “Pseudotumor Cerebri” in Chap. 30.


Neurology_Adams

Neurology_Adams. The examiner is also aided by the fact that papilledema due to raised intracranial pressure is generally bilateral, although, as mentioned earlier, the degree of disc swelling may not be symmetrical. In contrast, papillitis and infarction of the nerve head affect one eye, but there are exceptions to both of these statements. The pupillary reaction to light is muted only with infarction and optic neuritis, not with acute papilledema (once secondary optic atrophy supervenes, the loss of afferent light reaction is indeed observed). The occurrence of papilledema on one side and optic atrophy on the other is referred to as the Foster Kennedy syndrome; it is typically caused by a frontal lobe tumor or an olfactory meningioma on the side of the atrophic disc. In its complete form, which is seen only rarely, there is also anosmia on the side of the optic atrophy. Another cause of the same funduscopic appearance has been called the “pseudo-Foster Kennedy syndrome,” which occurs when papillitis


Neurology_Adams

Neurology_Adams. rarely, there is also anosmia on the side of the optic atrophy. Another cause of the same funduscopic appearance has been called the “pseudo-Foster Kennedy syndrome,” which occurs when papillitis in one eye occurs years after an optic neuropathy with disc pallor in the fellow eye.


Neurology_Adams

Neurology_Adams. Chronic papilledema represents a risk for permanent reduction in vision from secondary optic atrophy. Repeated testing of visual acuity is often inadequate to assess a patient’s course; serial evaluation of the visual fields, by automated perimetry or tangent screen testing, is sensitive to changes in field constriction that raise concern for ensuing optic atrophy.


Neurology_Adams

Neurology_Adams. The essential element in the pathogenesis of papilledema is an increase in pressure in the sheaths surrounding the optic nerves, which communicate directly with the subarachnoid space of the brain. This was demonstrated convincingly by Hayreh (1964), who produced bilateral chronic papilledema in monkeys by inflating balloons in the subarachnoid space and then opening the sheath of one optic nerve; the papilledema promptly subsided on the operated side but not on the opposite side. The appearance of the swollen disc has been specifically ascribed to a blockage of axoplasmic flow in the optic nerve fibers (Minckler et al; Tso and Hayreh). It was found that compression of the optic nerve by elevated cerebrospinal fluid (CSF) pressure resulted in swelling of axons behind the optic nerve head and leakage of their contents into the extracellular spaces of the disc. The block in axoplasmic flow alone, however, probably does not account for the marked congestion of vessels and hemorrhages


Neurology_Adams

Neurology_Adams. and leakage of their contents into the extracellular spaces of the disc. The block in axoplasmic flow alone, however, probably does not account for the marked congestion of vessels and hemorrhages that accompany papilledema and an additional component of vascular congestion is likely.


Neurology_Adams

Neurology_Adams. The mechanism of papilledema that on rare occasions accompanies spinal tumors, particularly oligodendrogliomas, and the Guillain-Barré syndrome is not entirely clear. Usually the CSF protein is more than 1,000 mg/100 mL, but this cannot be the entire or only explanation, as instances occur in which the protein concentration is only slightly elevated (also the concentration of protein in the ventricular and cerebral subarachnoid spaces is considerably lower than in the lumbar sac, where it is usually sampled; see Chap. 29). In other diseases that at times give rise to papilledema—e.g., chronic lung disease with hypercapnia, cancer with meningeal infiltration, or dural arteriovenous malformation—the mechanism is most often a generalized increase of intracranial pressure. Other causes of papilledema are cyanotic congenital heart disease, and other forms of polycythemia, hypocalcemia though an obscure mechanism, and POEMS syndrome (polyneuropathy, organomegaly, endocrinopathy, monoclonal


Neurology_Adams

Neurology_Adams. are cyanotic congenital heart disease, and other forms of polycythemia, hypocalcemia though an obscure mechanism, and POEMS syndrome (polyneuropathy, organomegaly, endocrinopathy, monoclonal gammopathy, and skin changes; see Chap. 43).


Neurology_Adams

Neurology_Adams. Diseases of the Optic Nerves The optic nerves constitute the axonal projections of the retinal ganglion cells to the lateral geniculate bodies and other sites. Their proximal portion, the optic nerve head, can be visually inspected and changes in the optic disc are therefore of particular importance. These changes may reflect the presence of raised intracranial pressure as already described; optic neuritis (“papillitis”); infarction of the optic nerve head; congenital defects of the optic nerves (optic pits and colobomas); hypoplasia and atrophy of the optic nerves; and glaucoma. Illustrations of these and other abnormalities of the disc and ocular fundus can be found in the atlas by E.M. Chester and in the text by Biousse and Newman. In general, optic neuropathies are distinguished from other causes of visual loss by a predominance of loss of color vision and by the presence of an afferent pupillary defect.


Neurology_Adams

Neurology_Adams. Table 12-3 lists the main causes of optic neuropathy, which are discussed in the following portions of this chapter. Optic Neuritis (See Chap. 35) This inflammatory process causes unilateral acute impairment of vision that may appear in one or both eyes, either simultaneously or successively. It develops in a number of clinical settings, but has a special relationship to multiple sclerosis. The most common situation is one in which an adolescent or young adult woman has a rapid diminution of vision in one eye as though a veil had covered the eye, progressing within hours or days. Pain on movement of the globe is a common, but not universal reported symptom (Table 12-2). The swinging flashlight test usually confirms a relative afferent pupillary defect on the affected side, unless the fellow eye has previously been affected.


Neurology_Adams

Neurology_Adams. The optic disc and retina appear normal in the majority of cases, in which the condition is of the more common retrobulbar variety. However, if the inflammation is near the nerve head, there is swelling of the disc (papillitis) (Fig. 12-14). The disc margins are then seen to be elevated, blurred, and, rarely, surrounded by hemorrhages. Inflammatory sheathing of the retinal veins, as described by Rucker, is known to occur but has been uncommon in our patients. In extreme cases, edema may suffuse from the disc to cause a rippling in the adjacent retina.


Neurology_Adams

Neurology_Adams. After several weeks to months, there is spontaneous recovery; vision returns to normal in more than two-thirds of cases. Recovery of vision occurs spontaneously, or may be hastened by the intravenous administration of high doses of corticosteroids (see “Treatment of Optic Neuritis” in Chap. 35). Diminution of brightness, dyschromatopsia, or a scotoma may remain; rarely, the patient is left with severe permanent visual deficits. Often, patients report a transient increase in blurring with exertion or with exposure to heat (Uhthoff phenomenon).


Neurology_Adams

Neurology_Adams. Despite the return of visual acuity in the majority of patients with optic neuritis, a degree of optic atrophy almost always results. The disc then appears pale, particularly in its temporal sector (temporal pallor), and the pallor extends beyond the margins of the disc into the peripapillary retinal nerve fibers. The pattern-shift visual evoked potential remains delayed; as a result, this test is a highly sensitive indicator of previous, even asymptomatic, episodes of optic neuritis.


Neurology_Adams

Neurology_Adams. As time progresses, more than half of adults with idiopathic optic neuritis will develop other symptoms and signs of multiple sclerosis within 5 years, and even more do so when they are observed for longer periods. Conversely, in approximately 15 percent of patients with multiple sclerosis, the history discloses that retrobulbar neuritis was the first symptom. A proportion of patients with acute optic neuritis are found at the time of an acute attack to have characteristic subclinical radiographic features of multiple sclerosis on MRI of the cerebrum and spine. The treatment of optic neuritis is taken up with multiple sclerosis in Chap. 35. Optic neuritis is also a main component of neuromyelitis optica (Devic disease; see Chap. 35); the vision loss is often more severe and the prognosis for recovery is poorer than for optic neuritis in multiple sclerosis.


Neurology_Adams

Neurology_Adams. Postinfectious demyelinating disease is a possible cause in some cases that do not later show signs of multiple sclerosis. Less is known about children with retrobulbar neuropathy, in whom the disorder is more often bilateral and frequently relates to a preceding viral infection (“neuroretinitis,” see the following text). Their prognosis is better than that of adults. Some cases of optic neuritis have been convincingly attributed to paranasal sinus disease, but this association only occurs rarely, as discussed further on. Neuroretinitis is a rare postor parainfectious process seen mostly in children and young adults, sometimes in association with exposure to the Bartonella henselae bacteria, the cause of cat scratch fever. Papillitis is accompanied by macular edema and exudates situated radially in the Henle layer, producing a “macular star” appearance.


Neurology_Adams

Neurology_Adams. In persons older than 50 years of age, a common cause of a persistent monocular loss of vision is ischemic infarction of the optic nerve head (Fig. 12-15). With anterior ischemic optic neuropathy, the optic disc is involved and optic disc edema is visualized in the acute phase. In contrast, with posterior ischemic optic neuropathy, there are no changes of the optic disc until disc pallor develops in the chronic stages. Ischemic optic neuropathy can be either arteritic (discussed in the following text) or nonarteritic. With nonarteritic anterior ischemic optic neuropathy (NAION), the onset is typically abrupt and painless, but on occasion the visual loss is progressive for several days. Usually, there are no premonitory symptoms or episodes of transient visual loss. The field defect is often altitudinal. If the area of central fixation is involved, then acuity can be severely compromised. Swelling of the optic disc is typical, and can be sectoral, with certain portions of the disc


Neurology_Adams

Neurology_Adams. often altitudinal. If the area of central fixation is involved, then acuity can be severely compromised. Swelling of the optic disc is typical, and can be sectoral, with certain portions of the disc circumference visibly spared. Associated small, flame-shaped hemorrhages are also typical. The retina and retinal vessels are not affected, as they are in cases of embolic occlusion of the central retinal artery.


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Neurology_Adams. Despite these distinctive features, ischemic optic neuropathy can sometimes be difficult to differentiate from optic neuritis, as pointed out by Rizzo and Lessell. This proves particularly problematic when visual loss evolves over days and mild pain accompanies the ischemic condition. However, the age of the patient and nature of the field defect (central in optic neuritis in contrast to sometimes altitudinal in ischemic neuropathy) further serve to clarify the situation. Furthermore, arteritic and nonarteritic forms of ischemic optic neuropathy are distinguished, the former being the result of temporal (giant cell) arteritis. The prognosis for visual recovery from nonarteritic anterior ischemic optic neuropathy is generally poorer than for other forms of optic neuropathy. As the disc edema subsides, optic atrophy becomes evident. The second eye may be similarly affected at a later date, particularly in those patients with hypertension and diabetes mellitus.


Neurology_Adams

Neurology_Adams. As to the pathogenesis of nonarteritic anterior ischemic optic neuropathy, it has been attributed by Hayreh to insufficiency of the posterior ciliary artery circulation and more specifically to occlusion of the branches of the peripapillary choroidal arterial system. A “crowded” optic disc, with small cup-to-disc ratio, is a risk factor. Most cases occur on a background of hypertensive vascular disease and diabetes, Nocturnal hypotension may be a contributing factor, and patients are often counseled to avoid medications that could cause the blood pressure to decline overnight. Nonarteritic anterior ischemic optic neuropathy may also complicate intraocular surgery.


Neurology_Adams

Neurology_Adams. A possible relationship has been observed between ischemic optic neuropathy and the use of nitric oxide inhibitors, such as sildenafil, for erectile dysfunction. The visual loss has occurred within 24 h of taking the drug and is usually unilateral. According to Pomeranz and colleagues, all affected patients have had risk factors for vascular disease such as hypertension, diabetes, or hyperlipidemia, but there have been exceptions, and these risk factors are likely to be present in older men who are also likely to use the drug.


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Neurology_Adams. Massive blood loss or intraoperative hypotension, particularly in association with the use of cardiac surgery with a bypass pump, may also produce visual loss, and ischemic infarction of the retina and optic nerve. Prolonged laminectomy operations, performed with the patient in the prone position, are another situation that can be complicated by severe unilateral or bilateral ischemic optic neuropathy. Obese individuals and those with small optic cups are seemingly at risk for this complication. The reported cases have been summarized from a registry by Lee and coworkers.


Neurology_Adams

Neurology_Adams. Temporal, or giant cell, arteritis is another important cause of ischemic optic neuropathy (see also Chap. 9 on the related headache and Chap. 33 for a discussion of cerebrovascular disease in association with giant cell arteritis). Fleeting premonitory symptoms of visual loss (amaurosis fugax) may precede infarction of the nerve. Infarction caused by cranial arteritis may affect both optic nerves or retina in close succession and also, less often, impair ocular motor function.


Neurology_Adams

Neurology_Adams. A number of disease processes adjacent to the orbit and optic nerve can cause blindness, usually with signs of compression or infarction of the optic and oculomotor nerves. They are seen far less frequently than are ischemic optic neuropathy and optic neuritis. Septic cavernous sinus thrombosis (see “Cavernous Sinus Thrombosis” in Chap. 33), for example, may be accompanied by loss of vision in one or both eyes. Visual loss may present days after the development of chemosis and oculomotor palsies from the venous sinus occlusion. The mechanism of visual loss, which can occur without swelling of the optic nerve head, is unclear but most likely relates to retrobulbar ischemia of the nerve.


Neurology_Adams

Neurology_Adams. Similarly, optic and oculomotor disorders may rarely complicate ethmoid or sphenoid sinus infections. Severe diabetes with mucormycosis or other invasive fungal or bacterial infection is the usual setting for these complications. Extensive sinus disease may occasionally produce optic neuropathy; for example, Slavin and Glaser described a case of loss of vision from a sphenoethmoidal sinusitis with cellulitis at the orbital apex. Visual symptoms in these exceptional circumstances can occur prior to overt signs of local inflammation. An otherwise benign sphenoidal mucocele may cause a compressive optic neuropathy, usually with accompanying ophthalmoparesis and slight proptosis.


Neurology_Adams

Neurology_Adams. Simultaneous impairment of vision in the two eyes, with central or centrocecal scotomas, is often caused by nutritional deficiency. This occurrence is observed most often in the chronically alcoholic or malnourished patient. Impairment of visual acuity evolves over several days to weeks, and examination discloses bilateral, roughly symmetrical central or centrocecal scotomas, with the peripheral fields being intact. With appropriate treatment (nutritious diet and vitamins B) instituted soon after the onset of visual loss, recovery is possible. If treatment is delayed, patients are left with varying degrees of permanent defect in central vision and pallor of the temporal portions of the optic discs. This disorder has been referred to as “tobacco-alcohol amblyopia,” the implication being that it is caused by the toxic effects of tobacco or alcohol or both. In fact, the problem is more likely one of nutritional deficiency and is more properly designated as deficiency amblyopia or


Neurology_Adams

Neurology_Adams. that it is caused by the toxic effects of tobacco or alcohol or both. In fact, the problem is more likely one of nutritional deficiency and is more properly designated as deficiency amblyopia or nutritional optic neuropathy (see Chap. 41). The same disorder may be seen under conditions of severe dietary deprivation (see Chap. 41) and in patients with vitamin B12 deficiency.


Neurology_Adams

Neurology_Adams. A subacute optic neuropathy of possible toxic origin was described in Jamaican natives. It was characterized by bilaterally symmetrical central visual loss and had additional features of nerve deafness, ataxia, and spasticity in some cases. A similar condition is described periodically in other Caribbean countries, two decades ago in Cuba, where an optic neuropathy of epidemic proportions was associated with a sensory polyneuropathy. A nutritional etiology, possibly contributed to by tobacco use (putatively cigars in the Cuban epidemic), was the likely cause of these outbreaks (see Sadun et al and The Cuba Neuropathy Field Investigation Team report). A putative role of exposure to cyanide, either from smoking or consumption of cassava, has been a feature of some of these epidemics.


Neurology_Adams

Neurology_Adams. Impairment of vision because of methanol intoxication is abrupt in onset and characterized by large symmetrical central scotomas as well as symptoms of acidosis. Treatment is directed mainly to correction of the acidosis and possibly, the administration of fomepizole. The same may occur with ethylene glycol ingestion. In contrast, the subacute development of central field defects is attributable to toxins and other prescribed therapeutic agents, notably ethambutol, linezolid, isoniazid, streptomycin, chloramphenicol, methotrexate, and chlorpropamide. Infliximab and other TNF-alpha blocking medications can occasionally precipitate optic neuritis and other demyelinating syndromes of the central or peripheral nervous system. The main drugs reported to have a toxic effect on the optic nerves are listed in Table 12-3 and have been catalogued more extensively by Grant. Hereditary Abnormalities of the Optic Nerve


Neurology_Adams

Neurology_Adams. Hereditary Abnormalities of the Optic Nerve Several optic neuropathies have a recognized genetic etiology. As the number of identified pathogenic genetic variations increases, it becomes more challenging to match specific phenotypes and genotypes. Leber hereditary optic neuropathy, a maternally inherited mitochondrial disorder, is an infrequent but important cause of blindness that usually presents in young adults. It may simulate the more common inflammatory optic neuropathies that also cause a relatively abrupt onset of visual loss, and in some cases also shows some degree of recovery (see “Hereditary Optic Atrophy of Leber” in Chap. 36). The visual field defect typically takes the form of a severe cecocentral scotoma.


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Neurology_Adams. The presentation of dominant optic atrophy, known as Kjer optic neuropathy, is usually less dramatic; it presents with insidious, bilateral vision loss. The abnormality might be detected, for example, during a vision screening test in the early years of school. Vision is typically modestly reduced, but the optic discs can show significant temporal pallor, with an excavated appearance. The condition shows mendelian autosomal dominant pattern because it is caused by a nuclear genetic mutation, although the dysfunctional protein causes a mitochondrial metabolic defect. Some patients have dominant optic atrophy “plus,” in which the syndrome may include other abnormalities such as hearing loss or peripheral neuropathy. Developmental Abnormalities of the Optic Nerve


Neurology_Adams

Neurology_Adams. Developmental Abnormalities of the Optic Nerve Congenital cavitary defects of the optic disc can arise from defective closure of the optic fissure during embryogenesis. These defects, known either as an optic pit or as a larger optic coloboma, may cause impaired vision when the papillomacular bundle is affected. Usually the abnormality is unilateral and unassociated with developmental abnormalities of the brain. A hereditary form is known (Brown and Tasman). Optic nerve hypoplasia refers to nerves with abnormally small diameter. Funduscopic examination may reveal the “double ring” sign, referring to a small optic disc within the larger opening of the scleral canal. Optic nerve hypoplasia can be part of the de Morsier syndrome, which includes cortical heterotopias and other midline patterning deficits such as absence of the septum pellucidum and hypothalamic-pituitary abnormalities.


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Neurology_Adams. Optic nerve and chiasmal compression and infiltration by gliomas, meningiomas, craniopharyngiomas, and metastatic tumors may cause loss of vision and optic atrophy (see Chap. 30). Pituitary tumors characteristically cause bitemporal hemianopia, but very large adenomas can cause vision loss that also extends through the nasal hemifield of one or both eyes (see “Pituitary Apoplexy” in Chap. 30). Pituitary apoplexy, referring to acute involutional hemorrhage into a pituitary adenoma, presents with an acute headache that may be accompanied by visual loss from compression of the optic nerves and chiasm, as well as ocular motility deficits.


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Neurology_Adams. Of particular importance is the optic nerve glioma that occurs either sporadically or in patients with type I von Recklinghausen neurofibromatosis. Usually, it develops in children, often before the fourth year, causing a mass within the orbit and progressive loss of vision. If the eye is blind, the recommended therapy is surgical removal to prevent extension into the optic chiasm and hypothalamus. If vision is retained, patients may be observed carefully, but if vision declines, radiation and chemotherapy are often recommended forms of treatment. Although most such gliomas are of low grade, malignant forms (glioblastoma) can also occur in adults.


Neurology_Adams

Neurology_Adams. Radiation-induced damage of the optic nerves and chiasm has been well documented. It is typically delayed, occurring at an average of 18 months after radiation exposure, and is often accompanied by enhancement of the nerve on MRI. It is more common following radiation doses in excess of 50 Gy (5,000 rad) (see Jiang et al). In a series of 219 patients at the M.D. Anderson Cancer Center who received radiotherapy for carcinomas of the nasal or paranasal region, retinopathy occurred in 7, optic neuropathy with blindness in 8, and chiasmatic damage with bilateral visual impairment in 1. Attempted treatment strategies have included corticosteroids, hyperbaric oxygen, and the VEGF-inhibitor bevacizumab, but all show very limited results. This topic is also addressed in Chap. 30.


Neurology_Adams

Neurology_Adams. Infiltration of an optic nerve may occur in sarcoidosis (see Fig. 31-4, bottom panel), granulomatosis with polyangiitis (formerly Wegener granulomatosis), and with certain neoplasms, notably leukemia and lymphoma. Systemic lupus erythematosus, diabetes, sarcoidosis, neurosyphilis, and AIDS also rarely give rise to optic neuropathies. The condition called “orbital pseudotumor,” essentially an inflammatory condition of all the orbital contents, can include visual loss from optic neuropathy, and is discussed in Chap. 13. Lesions of the Chiasm, Optic Tract, and Geniculocalcarine Pathway Hemianopia describes visual loss in one-half of the visual field for each eye. Bitemporal hemianopia is heteronymous, because the field deficit is on opposite sides of the vertical meridian for each eye. Bitemporal hemianopia is caused by a lesion that disrupts the decussating fibers of the optic chiasm and is caused most often by the suprasellar extension of a tumor of the pituitary gland (see


Neurology_Adams

Neurology_Adams. Fig. 12-2C). It may also be the result, at this same site, of a craniopharyngioma, Rathke cleft cyst, a saccular aneurysm or dolichoectatic artery of the anterior circle of Willis, and a meningioma of the tuberculum sellae; less often, it may be a result of sarcoidosis, metastatic carcinoma, ectopic pinealoma or dysgerminoma, Hand-Schüller-Christian disease, opticochiasmic arachnoiditis, or hydrocephalus with dilatation and downward herniation of the anterior part of the third ventricle (Corbett). In some instances a tumor pushing upward presses the medial parts of the optic nerves, just anterior to the chiasm, against the anterior cerebral arteries.


Neurology_Adams

Neurology_Adams. Variations in the pattern of visual loss from chiasmal lesions are frequent, in part accounted for by the location of the chiasm in an individual patient. A “postfixed” chiasm is located more posteriorly, and a compressive lesion arising from the pituitary sella is more likely to present with deficits relating to optic neuropathy. In contrast, a prefixed chiasm is located more anteriorly, so that a compressive lesion from the pituitary sella is more likely to compress the optic tract rather than the optic chiasm. As noted previously, the visual field pattern created by a lesion of the optic nerve as it joins the chiasm typically includes a scotomatous defect on the affected side coupled with a contralateral superior quadrantanopia (a combination referred to as a “junctional field defect”). The latter is caused by interruption of nasal retinal fibers from the contralateral optic nerve. This was originally attributed to fibers from the inferonasal retina projecting into the base of the


Neurology_Adams

Neurology_Adams. The latter is caused by interruption of nasal retinal fibers from the contralateral optic nerve. This was originally attributed to fibers from the inferonasal retina projecting into the base of the affected optic nerve before looping back to decussate through the chiasm; however, there is now evidence against the normal existence of this structure and discussed in the reference by Horton.


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Neurology_Adams. Homonymous hemianopia (loss of vision in corresponding halves of the visual fields) signifies a lesion of the visual pathway behind the chiasm. When a homonymous hemianopia is complete, it is difficult to discern the localization within the retrochiasmal visual pathways on the basis of the field loss alone. In contrast, incomplete homonymous hemianopia has more localizing value. If the field defects in the two eyes are identical (congruous), the lesion is likely to be posterior, in the calcarine cortex and subcortical white matter of the occipital lobe. In contrast, if the incomplete homonymous deficit has a different pattern in each eye (with one eye showing greater field loss than the other, but both on the same side of the vertical meridian), the pattern is incongruous, and the localization is more anterior within the retrochiasmal pathways, with the optic tract or proximal optic radiations most likely to be implicated. In this portion of the visual pathways, the crossing axons


Neurology_Adams

Neurology_Adams. is more anterior within the retrochiasmal pathways, with the optic tract or proximal optic radiations most likely to be implicated. In this portion of the visual pathways, the crossing axons from one eye are in the process of becoming juxtaposed with their paired axon from the fellow eye, and a partial lesion may disproportionately affect more of the fibers from one eye than the other. Absolute congruity of field defects is actually infrequent, even with occipital lesions.


Neurology_Adams

Neurology_Adams. The lower fibers of the geniculocalcarine pathway (from the inferior retinas) swing in a wide arc over the temporal horn of the lateral ventricle and then proceed posteriorly to join the upper fibers of the pathway on their way to the calcarine cortex (see Fig. 12-2). This arc of fibers is known variously as the Flechsig, Meyer, or Archambault loop, and a lesion that interrupts these fibers will produce a contralateral superior homonymous quadrantanopia (upper temporal deficit in the contralateral eye and upper nasal deficit in the ipsilateral eye; Fig. 12-2E), or in incomplete cases, a homonymous superior wedge defect respecting the vertical meridian. This clinical effect was first described by Harvey Cushing, so that his name also was in the past applied to the loop of temporal visual fibers. Parietal lobe lesions are said to affect the inferior quadrants of the visual fields more than the superior ones.


Neurology_Adams

Neurology_Adams. Just as with the contralateral representation of the visual fields in respect to the vertical meridian, the representation of the upper visual field is in the bank of neurons below the calcarine fissure and vice versa. As to the localizing value of quadrantic defects, the report of Jacobson is of interest; he found, in reviewing the imaging studies of 41 patients with inferior quadrantanopia and 30 with superior quadrantanopia, that in 76 percent of the former and 83 percent of the latter the lesions were confined to the occipital lobe.


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Neurology_Adams. If the entire optic tract or calcarine cortex on one side is destroyed, the homonymous hemianopia is complete. However, with infarction of the occipital lobe as a result of occlusion of the posterior cerebral artery, the macular region, represented in the most posterior part of the striate cortex, may be spared by virtue of collateral circulation from branches of the middle cerebral artery. In this circumstance, there is a 5to 10-degree island of vision around the fixation point on the side of the hemianopia (macular sparing). With other types of destructive lesions, this effect is not seen. Lesions of both occipital poles result in bilateral central scotomas. If all the calcarine cortex or all the subcortical geniculocalcarine fibers on both sides are completely destroyed, the bilateral hemianopias cause cerebral, or “cortical,” blindness (see the following text and Chap. 21).


Neurology_Adams

Neurology_Adams. An altitudinal defect is one that is confined by a horizontal border and crosses the vertical meridian. Homonymous altitudinal hemianopia is usually caused by lesions of both occipital lobes below or above the calcarine sulcus, and rarely to a lesion of the optic chiasm or nerves. The most common cause of this rare phenomenon is still occlusion of both posterior cerebral arteries. Herniation of the occipital lobe over the tentorial margin can produce a homonymous superior altitudinal defect by selectively compressing the inferior branches of the posterior cerebral arteries. A monocular altitudinal hemianopia, by contrast, is almost invariably an optic neuropathy, usually the nonarteritic anterior ischemic type that arises from occlusion of the posterior ciliary vessels.


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Neurology_Adams. In certain instances of homonymous hemianopia, the patient is capable of some visual perception in the hemianopic fields, a circumstance that permits the study of the vulnerability of different visual functions. For example, colored targets may be detected in the hemianopic fields, whereas achromatic ones cannot. The tendency for patients with occipital lesions to have greater sensitivity for kinetic stimuli than for static ones was described by Riddoch in 1917. But even in seemingly complete hemianopic defects, in which the patient consciously admits to being blind, it has been shown that he may still react to visual stimuli when forced-choice techniques are used. Blythe and coworkers found that 20 percent of their patients with no ability to discriminate patterns in the hemianopic field nonetheless could still reach accurately and look at a moving light in the “blind” field. This type of residual visual function has been called “blindsight” by Weiskrantz and colleagues. These


Neurology_Adams

Neurology_Adams. field nonetheless could still reach accurately and look at a moving light in the “blind” field. This type of residual visual function has been called “blindsight” by Weiskrantz and colleagues. These residual visual functions are generally attributed to the preserved function of retinocollicular or geniculoprestriate cortical connections, but in some cases, they may be a result of sparing of small islands of calcarine neurons.


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Neurology_Adams. In yet other instances of complete homonymous hemianopia, the patient may be little disabled by visual field loss (Benton et al; Meienberg). This is because of preservation of vision in a small part of the visual field known as the monocular temporal crescent, which is the peripheral portion of the visual field, between 60 and 90 degrees from the fixation point, that is represented in the most anterior part of the visual striate cortex. In particular, the temporal crescent is sensitive to moving stimuli, allowing the patient to avoid collisions with people and objects. Blindness in the Hysterical or Malingering Patient