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Understanding the Lingo

Terms associated with vision

Term
Definition
Accommodation Adjustment of the eye for seeing at different distances, accomplished by contraction or relaxation of the muscles that change the shape of the lens, accompanied by changes in the pupil size.
Acuity Sharpness of vision. Ability of the eye to distinguish detail, especially for reading.
Amblyopia Reduced functional vison in one eye, uncorrectable by standard procedures, ie: application of lenses.
Astigmatism Refractive error which prevents light rays from coming to a point or focus on the retina, caused by unequal degrees of refractive power in the cornea.
Binocular Fixation Ability to use the two eyes simultaneously to focus on a target and fuse the two images into a single one, giving correct interpretation of its position in space and its depth.
Central Vision Ability of the eye to perceive a target in the direct line of vision.
Convergence Process of using extraocular muscles to direct the visual axes of the two eyes to a near point (simultaneous turning of the eyes inward).
Cortical Visual Impairment Disturbance of posterior visual pathway or cortex.
Divergence Process of using extraocular muscles to direct the visual axes of the two eyes to a point further away (simultaneous turning of the eyes outward).
Esophoria/Esotropia Tendency of the eyes to turn inward.
Exophoria/Exotropia Tendency of the eyes to turn outward.
Field The entire area that can be seen while the eye is fixing or gazing steadily at a target in the direct line of vision.
Fixation Direction of gaze whereby the image of the target falls on the fovea centralis , which is the depression in the center of the macula where vision is most acute.
Heterophoria Tendency of the eyes to deviate.
Heterotropia Deviation of the eyes from the normal straight position.
Hyperopia / Hypermetrophia (farsightedness) Refractive error in which the focal point for light rays from a distant object is posterior to the retina when accommodation is at rest.
Hyperphoria Tendency toward upward deviation of one eye.
Hypertropia Upward deviation of one eye.
Legally blind In the educational context this indicates that a person has less than 20/200 vision in the better eye or a very limited field of vision (20 at its widest point)
Low vision In the educational setting this generally refers to a severe visual impairment, not necessarily limited to distance vision. It applies to those who are unable to read the newspaper at the normal viewing distance with eyeglasses or contacts. They use a combination of vision and other senses to learn, and sometimes braille.
Monocular Fixation Ability to direct the fovea (which is the depression in the center of the macula where vision is most acute) to a target and maintain the match.
Myopia Refractive error in which the focal point for light rays from a distant object is anterior to the retina when accommodation is at rest.
Nystagmus "Dancing eyes" Involuntary oscillatory movements of the eyeball in horizontal, vertical, rotary or mixed directions. May not have depth perception. It increases with stress, fatigue, or focusing.
Occlusion Covering one eye to encourage use of the other.
OD Oculus dexter (right eye).
Optic Nerve The nerve carrying visual impulses from the retina to the brain, where images are formed.
OS Oculus sinister (left eye).
OU Oculi unitas (both eyes).
Partially sighted In the educational setting indicates some type of visual problem has resulted in a need for special education.
Peripheral Vision Ability to perceive presence and motion of targets outside the direct line of vision.
Refraction Determination of refractive error os the eye and correction by prescriptive lenses.
Retinopathy of Prematurity (ROP) It is related to premature birth and immaturity of the visual system. For some reason the premature eye is unable to respond to the normal distribution of nutrients causing blood vessels to rupture. The rupturing of these vessels causes scarring of the retina. Sometimes the condition heals itself within the first year. Sometimes surgery can restore vision by re-attaching the retina. Sometimes the problem cannot be resolved. Vision can vary from good, to guarded, to blind.
Strabismus Inability of the two eyes to simultaneously direct the visual axes to the same target.
Totally Blind Students who learn through braille or other non visual media.
Tracking Ability to follow horizontal, vertical, circular, or diagonal movements of targets with smooth pursuit eye movements.
 
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Last modified: January 26, 2013