20/20 vision: Expression for normal visual acuity measured at a distance of 20 feet. 20/20 vision means you can see clearly at 20 feet what should normally be seen at 20 feet. 20/80 vision means that you can see at 20 feet what a person with normal vision can see at 80 feet.

Acuity: The clarity or sharpness of vision.

Amblyopia: Amblyopia is poor vision in an eye that otherwise appears normal. It is sometimes called “lazy eye.” Amblyopia occurs when the brain does not recognize the sight from that eye. Eventually, the brain stops using the weaker eye, causing poor vision or even blindness in that eye.

Amplitude: Size of the evoked potential generated by the brain (also known as magnitude).

Astigmatism: A defect in a curvature of the cornea or lens of the eye. As a result, a ray of light is not sharply focused on the retina but is spread irregularly.

Cornea: Transparent anterior portion of the outer covering of the eye; it covers the lens and iris and is continuous with the sclera.

Diabetic Retinopathy: Diabetic retinopathy is damage to the eye’s retina that occurs with long-term diabetes. See FAQs for more information on retinopathy and diabetes.

Electronic Response: A signal that is produced in direct correlation to the stimulus.

Eye care specialist: Generally an optometrist or ophthalmologist who performs eye exam tests to help diagnose and treat disorders relating to the eye and vision.


Hyperopia: Farsightedness; a person can see distant objects more clearly than close objects. A refractive error in which the eyeball is too short from front to back or the refractive power of the eye is too weak, so that parallel rays of light brought to a focus behind the retina.

Impulse: The electrical discharge that travels along a nerve fiber.

Intraocular Pressure (IOP): is a measurement of the fluid pressure inside the eye.

Latency: The time that elapses between a stimulus and the response to it.

Lens: Part of the eye that is transparent and is used to converge or diverge transmitted light and to form images.

Lateral Geniculate Nucleas (LGN): Distributes the electric signal to the visual cortex.

Magnitude: Size of the evoked potential generated by the brain(also known as amplitude).

Misalignment: A muscle imbalance where the two eyes are not aligned either horizontally, vertically or both. See strabismus.

Monocular blindness: Blindness in one eye.

Multiple Sclerosis (MS): Multiple sclerosis is an autoimmune disease that affects the central nervous system, specifically the brain and spinal cord.

Myopia: Nearsightedness; a person can see near objects clearly while distant objects appeared blurred. A refractive error in which the eyeball is too long or the refractive power to strong, so that parallel rays of light are focused in front of the retina.

Non-Invasive: For the purposes of an eye exam this means no drops or touching the eye in any way.

Ophthalmologist: A medical doctor specializing in the treatment of diseases of the eye and vision. See FAQs for more information on ophthalmologist versus optometrist.

Optometrist: An eye specialist trained to diagnose, treat and monitor eye and vision care, eye diseases and related conditions, and prescribe eyeglasses, contact lenses, and medications to treat eye disorders.

Optic Nerve: Delivers the electrical signal from the retina to the Lateral Geniculate Nucleus.

Phase: Latency of the signal from the eye to the visual cortex of the brain.

Pre-Verbal: Before talking.

Pre-Literate: Before reading.

Refractive Error: A defect in the eye that prevents light rays from being brought to a sharp focus exactly on the retina. The amount of myopia, hyperopia or astigmatism presents in the eye.

Retina: The sensory membrane that lines the eye, receives the image formed by the lens, is the immediate instrument of vision, and is connected with the brain by optic nerve.

Spatial Frequency: Grading frequency that is equivalent to the Snellen eye chart.

Snellen Acuity Chart: Display consisting of a printed card with letters and numbers in lines decreasing in size; eye exam test used to test visual acuity.

Strabismus: The two eyes are not directed at the same point; misalignment of the eye.

Sweeps: Predetermined set of patterns.

Traumatic Brain Injury (TBI): a form of acquired injury to brain, occurs when a sudden trauma causes damage to the brain. See FAQs section for symptoms of brain injury.

Visual Cortex: The cortical area that receives information from the lateral geniculate body of the thalamus.

Visual Evoked Potential (VEP): An electrical signal generated in response to a known visual stimulus. See FAQs for more information related to vision care and the eye test related to VEP.