University of Iowa Health Care

Ophthalmology and Visual Sciences

Definition of Terms

Common Abbreviations:

BCVA: Best corrected visual acuity

EOM: Extraocular muscles

HPI: History of present Illness

IOL: Intraocular lens

POH: Past Ocular History

OD: right eye

OS: left eye

OU: both eyes

Note: The American Academy of Ophthalmology has a series of excellent diagrams of the anatomy of the eye that may help the layperson understand these definitions.

Definitions as pertaining to ophthalmology & visual sciences

Altitudinal visual field defects: This term describes a visual field defect in which either the upper or lower half of the visual field is selectively affected. The selective abnormality often creates a horizontal line across the visual field (known as "respecting the horizontal meridian"). Altitudinal defects occur in retinal vascular disease, glaucoma, and other disorders that affect the eye itself.

Amblyopia: A typically monocular (affecting one eye) visual deficit caused by an abnormality of the neural connections between the eye and the brain that results from deficient or asymmetric input of visual stimulus during the first few years of life. The conditions that most commonly cause amblyopia are eye misalignment (strabismus), a significant difference in spectacle prescription (refractive error) between the two eyes (anisometropia), or interruption of the light path of one of the eyes (by cataract, scar, tumor, etc.). If amblyopia is not treated before the age of 8, the visual deficit is usually permanent.

Anisometropia: A large difference in refractive error (spectacle prescription) between the two eyes. If this goes uncorrected in young children, it can lead to amblyopia.

Autosomal: Often used in combination with the words "dominant" and "recessive" when discussing modes of genetic transmission. This refers to genes that are carried on the autosomes or autosomal chromosomes (chromosomes 1 through 22). This is in contrast to the genes carried on the sex determining chromosomes, X and Y.

Autosomal recessive: An inheritance pattern in which a person must inherit two copies of an abnormal gene (one from each parent) in order to develop the disease. If two individuals each carry one copy of an abnormal gene, then each child born to these two parents will have a 25% chance of receiving 2 copies of the abnormal gene and as a result, inherit the disease. Cystic fibrosis is an example of an autosomal recessive disease.

Bell's Phenomenon: Bell's phenomenon invloves the uppward movement of the eye associated with eyelid closure and is considered to be a protective mechanism. It is estimatd to occur in 50 to 75% of the population. It prevents tear film instability and ocular surface damage in eyes with lagophthalmos induced during surgery. (Yoon JS, Lew H, Lee SY. Bell's phenomenon protects the tear film and ocular surface after frontalis suspension surgery for congenital ptosis. J Pediatr Ophthalmol Strabismus. 2008 Nov-Dec;45(6):350-5. PubMed PMID: 19043946)

Blind spot (Natural or physiologic): A spot that normally appears during the mapping of visual fields that corresponds to the point at which the optic nerve enters the back of the eye.

Blepharoptosis, see Ptosis

Cecocentral scotomas: These are visual field defects that extend from the central vision to the natural blind spot. This type of field defect usually represents an insult to the cluster of retinal ganglion cells called the papillomacular bundle.

Coloboma, colobomata (plural): A congenital defect or split in the normal continuity of some part of the eye. For example, absence of part of the iris or lens.

Color blindness: see Dyschromotopsia.

Disk cupping: An enlargement of the cup or central depression in the optic nerve head. Cupping is visible when viewing the back of the eye with an ophthalmoscope. An enlarged cup especially if accompanied by a notch or a small spot of bleeding is a sign of glaucoma. Cupping is a clinical sign that indicates that a large number of nerve fibers in the optic nerve have been lost.

Dyschromatopsia: A general term for color vision abnormalities. Heritable dyschromatopsias include red (protan), green (deutan), and blue (tritan) color vision deficits. These deficits may be partial (-omaly) or complete (-opia). Red and green color vision defects are X-linked while loss of the blue receptor (tritanopia) is inherited in an autosomal recessive fashion.

Electroretinogram (ERG): A test that measures the electrical activity of the retina when exposed to flashes of light of varying intensity. Abnormalities in the electroretinogram typically occur in conditions that affect the photoreceptor cells (e.g. retinitis pigmentosa).

Embryotoxon: Opacity of the inner most surface of the cornea at the periphery. Congenital anomaly

Fundus: In ophthalmology, this term refers to the inner lining of the eye that is visible with an ophthalmoscope. It includes the retina and optic nerve head.

click for enlarged image. Normal or low tension glaucomaGlaucoma, Normal-tension: Glaucoma in which the intraocular pressure is normal but there is progressive optic nerve damage and visual field loss.

Goldmann visual field: A type of peripheral vision test in which progressively dimmer lights are moved from the peripheral vision into the central vision, using an instrument that allows the point at which the light is first seen to be accurately mapped.

Incomplete penetrance: The concept that even though several members of a family or population may have the same DNA mutation, not everyone with that mutation will have or develop the disease. This is in contrast to variable expressivity which means that people with the same disease have varying disease severity. Penetrance, in contrast, is more of a yes/no question – does or does not the person have the disease.

Ishihara plates: 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.

Isopter: 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.

Leber’s hereditary optic neuropathy (LHON): 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).

Low vision aids: aka Vision rehabilitation aids. 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.

Macula: 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.

Nagel anomaloscope: 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.

Neuroimaging: Technology that allows x-ray-type pictures to be taken of the head and brain. The advantage of this type of imaging, such as computed tomography (CT) and magnetic resonance imaging (MRI) scans, is that they enable the physician to see a cross-sectional image of the brain and eyes.

Orthophoric: Proper alignment of the two eyes. Absence of eye deviation.

Papillomacular bundle: 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.

Peripapillary atrophy: 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.

Photopic: 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.

Protanomalous: 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.

Ptosis, (ptotic,) Blepharoptosis : drooping of the upper eyelid.

Relative afferent pupillary defect (RAPD): 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.

Retinal ganglion cells: 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.

Scotopic: 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. Click of enlarged image

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

Tortuous retinal vessels: Retinal blood vessels with abnormal bends and twists.

Variable expressivity: 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.

Versions: Movements of both eyes at the same time. "Normal versions" means that the eyes move together normally in all positions of gaze.

X-linked: An inheritance pattern in which males are much more severely affected than females. An X-linked disease results from mutation of a gene that lies on the X chromosome. Females have two copies of the X chromosome (XX) while males only have one copy (XY). Consequently, if a female has one good copy and one defective copy, then the good copy usually compensates for the defect in the other X chromosome and protects the individual partially or totally from the disease. In contrast, when males inherit a mutant gene on their single X chromosome the disease usually becomes manifest. In this inheritance pattern, affected males always transmit their abnormal copy of the X chromosome to their daughters (who are then carriers), but cannot pass the disease on to their sons. A daughter of a carrier female has a 50% chance of being a carrier herself. A son of a carrier female has a 50% chance of inherited the disease. Hemophilia is an example of an X-linked condition.


  1. Cassin B, Rubin ML. Dictionary of eye terminology. 4th ed. Gainesville, Fla.: Triad Pub. Co.; 2001.
  2. Stedman TL. Stedman's medical dictionary for the health professions and nursing. Illustrated 5th ed. Philadlephia: Lippincott Williams & Wilkins; 2005.
  3. OMIM. Online Mendelian Inheritance in Man. Available at
last updated: 09-01-2013
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