Glossary of Eye Terms

A common type of color vision test that can help determine general and specific inherited color vision deficits. It consists of a series of color plates in which the test taker is asked to identify numbers or geometric shapes composed of specific colors that are hidden within a field of spots of very similar colors. People with normal color vision can see the numbers or geometric figures while people with abnormal color vision cannot. See Ishihara Test Ishihara

• A line connecting a series of points in a visual field at which a person is able to detect a certain size and intensity of light. Isopters in normal visual fields are oval in shape.

• A disease entity that most commonly affects young men in their teens and early twenties and causes significantly decreased central vision in both eyes. The genes that cause LHON are carried on small circular mitochondrial DNA molecules that are inherited from an individuals mother. This condition is extremely rare (affecting fewer than 1 per million people per year) and does not affect everyone who harbors the genetic defect. The visual field defects in LHON are typically cecocentral scotomas. There are three other eye diseases named after Theodore Leber: 1) Leber congenital amaurosis (blindness at birth) inherited in an autosomal recessive fashion, 2) Leber's stellate neuroretinopathy (a non-heritable condition associated with cat scratch disease) and 3) Leber's military aneurysms (a non-heritable vascular malformation of the retina similar to Coat's disease).

• The central portion of the retina that is responsible for central vision. An insult to the macula can cause loss of central vision and a significant decrease in visual acuity.

• A device that used to determine degree of red or green color vision deficit. A dial on the anomaloscope is adjusted until the viewer (patient) believes that the green-red balance is appropriate compared with a standard yellow light whose intensity can also be varied. When a person with normal color vision views the "match" made by a patient with abnormal color vision, a deficit in either red or green color vision is readily apparent.

• Optical Coherence Tomography
  • Optical coherence tomography (OCT) is a noninvasive imaging technology used to obtain high resolution cross-sectional images of the retina. OCT is similar to ultrasound testing, except that imaging is performed by measuring light rather than sound. OCT measures the retinal nerve fiber layer thickness in glaucoma and other diseases of the optic nerve.
  • Proper alignment of the two eyes. Absence of eye deviation.
  • A collection of retinal ganglion cells that carry the information from the macula (the central retina) to the optic nerve and on to the brain. If damaged, central visual field defects occur.
  • Thinning of the retina and retinal, pigment epithelium in the region immediately surrounding the optic nerve head. This can be seen in a number of pathologic and benign conditions.
  • In biology, photophobia (adjective: photophobic) refers to negative response to light. Also called "light sensitivity" this is an excessive sensitivity to light and the aversion to sunlight or well-lit places. In ordinary medical terms photophobia is not a morbid fear, but an experience of discomfort or pain to the eyes due to light exposure. May be associated with excessive tearing. There can be many causes including inflammation of the iris or cornea.
  • A condition of "light adaptation" that is used in retinal testing such as the electroretinogram. Light adaptation is accomplished by exposing a patients eyes to diffuse light of moderate intensity several minutes. This can be useful for determining the health of "cones," the fine detail and color perceiving cells in the retina.
  • Partial color deficiency affecting the ability to see the color red. There are three possible color vision deficits: red (protan), green (deutan), and blue (tritan). The suffixes –omaly and –opia indicate partial and complete color vision deficits, respectively. Therefore, a person who has tritanomaly will have a partial blue color vision deficit while a person who has deuteranopia will have a complete green color deficit.
  • An indication of damage to the visual system which is greater on one side than the other. The presence of a relative afferent pupillary defect (RAPD) means that the pupils constrict less when a light is directed into the affected eye than they do when the same light is directed into the normal (or less affected) eye . The presence of an RAPD usually indicates damage to the retina or optic nerve that results in diminished light impulses being transmitted from the eye to the brain on the affected side.
  • These cells transmit the information from the other layers of the retina to the brain. The axons of these cells make up the optic nerve. Retinal ganglion cells comprise the most superficial cell layer in retina and are susceptible to damage in a number of disease entities, including glaucoma.
  • A group of genetic eye conditions leading to chronic retinal degeneration, accompanied by abnormal deposits of pigment. The disease causes a progressive decrease in peripheral or side vision. Associated with night blindness, loss of peripheral vision, tunnel vision, decreased acuity, lack of depth perception, retinal scarring, and photophobia.
  • An area of partial alteration in the field of vision with partially diminished or entirely degenerated visual acuity which is surrounded by a field of normal vision.
  • A condition of "dark adaptation" that is used in retinal testing such as the electroretinogram. Dark adaptation is accomplished by placing black goggles over the patient's eyes for a predetermined period of time (usually about 30 minutes). This can be useful for determining health of "rods," or the dim light-detecting cells in the retina.
  SEPTO-OPTIC DYSPLASIA
  • Septo-optic dysplasia
    • A clinically heterogeneous disorder loosely defined by any combination of optic nerve hypoplasia, pituitary gland hypoplasia, and midline abnormalities of the brain, including absence of the corpus callosum and septum pellucidum.
    • A condition in which the eyes are not properly aligned with each other resulting in an inability to focus both eyes on a given point. Greek strabismos = squinting
    • A form of color blindness exhibiting loss of the blue receptor, inherited in an autosomal recessive fashion.
    • The idea that individuals with a particular disease process will not each experience the same severity of disease. For instance, one person may have a milder form of the disease while another person with the same disease has a more severe manifestation of the disease. This is in contrast to incomplete penetrance.
    • Devices such as magnifiers and closed circuit television sets that can help people with sub-normal vision see more and function better in day to day activities. Also known as Low Vision aids.
    • Field of vision: The entire area that can be seen when the eye is directed forward, including that which is seen with peripheral vision.
    • A visual field test is an examination that may be performed to analyze a patient's visual field. The test may be performed by a technician directly, with the assistance of a machine, or completely by an automated machine. Machine based tests aid diagnostics by allowing a detailed printout of the patient's visual field. See Perimetry