Visual acuity is notated in several different manners, the most common and well known of which is 20/something, referred to as the Snellen method or Snellen fraction. An easy way to interpret this notation is that the individual can see at 20 feet what an individual with "normal" acuity could see at whatever distance the denominator represents. 20/60 vision would translate into having to be at 20 feet to see a letter or object that someone with "normal" vision would see at a distance of 60 feet.
Note: 20/20 is the accepted standard, but is not the limit of human vision. Many people can see 20/15, i.e., they can see from 20 feet what the standard person must go in to 15 feet to decipher.
The ability of the human eye to change the point in space that is in clear focus by adjusting the shape of the eye's crystalline lens via muscle action.
The indication of the clarity of someone's vision.
An indication of whether or not the two eyes are both pointed at the object of regard. If properly aligned, the possibility of binocular (two-eyed) vision exists.
The presence of reduced acuity in one (or occasionally both) otherwise healthy eye(s) that is not immediately correctable with lenses. This is commonly referred to as "lazy eye" because it is sometimes the result of disuse.
A difference between the two eyes in the amount or type of refractive error.
Blurred vision resulting from distortion of the eye's image, usually a result of a nonspherical cornea.
The brain's combining of the images from the two eyes into a single impression.
color vision deficiency:
Difficulty with distinguishing one or more colors, typically an inherited deficiency of varying severity that is more common in males (8% prevalence) compared to females (1%).
The turning in of both eyes, like might occur when viewing an approaching or near object.
A clear and flexible body lying directly behind the iris in the eye that can change shape in response to muscle action so as to alter the optics of the eye and allow the eye to be focused clearly at differing distances.
The ability to perceive relative distance in space. This skill comes from learning to interpret size, shape, shadows and overlap, as well as the small discrepancy difference in the images received by each eye.
The ability to distinguish similarities and differences in stimuli.
The turning outward of both eyes, like might occur when a viewed object moves further away.
The condition of having no refractive error.
A prefix used to describe the eyes being more inward turned than appropriate.
A comprehensive evaluation used to make a diagnosis and recommendations for management and treatment.
A prefix used to describe the eyes being more outward turned than appropriate.
Describes that portion of the health evaluation devoted to viewing the external portion of the eye, i.e., lids, lashes, conjunctiva, cornea, pupils, etc.
Coordinated efforts of the six extraocular muscles attached to each eye usually resulting in aiming the eye in a new direction or at a new object.
The ability to sustain the eyes in one place for viewing an object.
A small depression in the center of the macular region of the retina containing only tightly packed cones where vision is the sharpest.
The precise alignment of the two eyes so that the images fall on corresponding places on each retina and the brain has the possibility of binocular or two-eyed vision.
history (case history):
Gathering information regarding past or present ocular and visual signs and symptoms, as well as additional relevant facts concerning health status and other life events.
A prefix used to describe the situation where one eye is pointed upward in relation to the other.
A refractive error of the eye where the image formed by the optics of the eye falls behind the plane of the retina, resulting in a blurred image. This image, to be clear, needs to be moved forward to the retinal plane by either action of the crystalline lens or placement of a convex lens in front of the eye.
A person who intentionally reports erroneous symptoms or subjective test responses.
A refractive error of the eye where the image formed by the optics of the eye falls in front of the plane of the retina, resulting in a blurred image. This image, to be clear, needs to be moved backward to the retinal plane by placement of a concave lens in front of the eye.
Known also as "jerky eyes," a condition where they eyes make involuntary movements, usually quite rapid and rhythmic.
In screening terms, the designation given when an individual meets the minimum criteria established for the screening.
A tendency for the eyes to want to turn from the object being viewed which can be either inward or outward and which must be overcome to maintain fusion.
The round opening in the center of the iris through which light passes on its way through the crystalline lens to the retina.
A reflexive reaction of the pupil to viewing distance, emotional state, or change in available light level such that the size of the pupillary opening increases or decreases.
Eye movements used to follow moving objects.
Sending an individual to another person who can provide needed services when a condition is suspected that requires different experience or training.
Involuntary response to a stimulus.
Lack of focus, by the optics of the eye, of an image on the retina. Typically classified as hyperopia, myopia and astigmatism.
Eye movements used to quickly relocate the eyes from one position of gaze to another.
The use of tests to determine whether or not an individual meets established criteria, the results of which are not diagnostic but rather are the basis for referral or non-referral for further testing.
The pinnacle of depth perception; subtle discrimination of depth based on the slightly different view each eye obtains. A high level of stereopsis cannot be achieved without accurate binocular alignment and fusion.
Lack of alignment of the two eyes such that both eyes do not point at the object being viewed. Commonly termed "cross-eyed" or "wall-eyed," one eye could either be turned inward or outward in relation to the other.
The subconscious blockage by the brain of the information coming from one eye when its presence causes confusion for visual processing.
Can be confusing because it has two different but frequently used meanings:
- following a moving object with the eyes, i.e., pursuits
- moving the eyes along the lines of print in reading, which is actually a series of saccades
Eye movements where the two eyes are moving toward or away from each other, i.e., convergence or divergence.
The ability to integrate together visual guidance and motor movements to accomplish tasks, such as reproducing forms.