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. |
