Guidelines for Vision Screening in Missouri Schools

APPENDIX E: Glossary

Amblyopia

An ocular condition in an otherwise healthy eye, in which there is an abnormality of cortical response in the occipital lobe of the brain due to insufficient or inadequate stimulation of the fovea, neural pathway and cortex that may result in unilateral vision loss if untreated. (Also known as lazy eye or weakness of sight)

Astigmatism

A refractive error of the eye in which, with accommodation suspended, the refracting power of the eye is not uniform in all directions such as that incoming rays of light in a single eye do not come together to focus at a single point but rather are focused at two or more points that usually results in blurred or partially blurred vision.

Binocularity

The characteristic of the eyes when binocular vision is intact. Used interchangeably with binocular vision and requires both ocular alignment and stereoacuity.

Denominator

The bottom half of the fraction that shows how far away a person with normal visual acuity can stand from the chart and still read the symbol.

Diplopia

Double vision or the perception of two images, one by each fovea, experienced when the eyes are intentionally crossed or out of alignment due to imbalance of the extraocular muscles.

Distance vision

The ability of the eye to see images clearly at a distance (often a great distance). The inability to see a distant object clearly is called myopia.

Esophoria

A type of heterophoria in which the eye deviates inward or nasally when covered, that is, when fusion is suspended.

Esotropia

A type of strabismus in which one or both eyes deviate inward toward the nose from a parallel axis of vision. (Also called convergent strabismus)

Exophoria

A type of heterophoria in which the eye deviates outward or laterally when covered, that is, when fusion is suspended.

Exotropia

A type of strabismus in which one or both eyes deviate outward away from the nose from a parallel axis of vision. (Also called divergent strabismus)

Heterophoria

A latent alignment disorderin which the eyes are not parallel during monocular vision, that is, when only one eye is seeing and binocularity and fusion are disrupted. (Also referred to as phoria)

Heterotropia

A manifest alignment disorder, or strabismus, in which one or both eyes deviate from parallelism when attempting to focus on a target while both eyes are open. (Also referred to as tropia)

Hypermetropia

A refractive error in which the light raysfrom an incoming visual image have not converged by the time they reach the retina. Used interchangeably with the term hyperopia. (Formerly called “farsightedness,” a sometimes confusing term no longer used.)

Hyperopia

A refractive error in which the light rays from an incoming visual image have not converged by the time they reach the retina. Used interchangeably with the term hypermetropia. (Formerly called “farsightedness,” a sometimes confusing term no longer used.)

Hypophoria

A type of heterophoria in which the eye deviates downward, when covered, while fusion is suspended.

Hypotropia

A type of strabismusin which one or both eyes deviate downward from a parallel axis of vision.

Legal blindness

Is defined as the best-corrected central vision of 20/200 or less, and peripheral vision of 20 degrees or less.

Myopia

The most common of the refractive errors in which light rays from an incoming visual image converge before they reach the retina, or preretinally. (Formerly called “nearsightedness,” a confusing term no longer used.)

Near vision

The ability of the human eye to see objects with clarity at close range, also termed near point acuity or near acuity. Optimal near vision requires both accommodation and convergence.

Nearsightedness

See Myopia.

Numerator

The top half of the fraction that stands for the distance the examinee is away from the chart.

Nystagmus

An involuntary, jerky movement of one or both eyes suggestive of primary ocular or systemic disease. (Also known as dancing eye or jerky eye)

Occluder

An object that temporarily obstructs vision during vision screening, preventing an eye from visualizing a focal target (e.g., paper cup, paper patch, palm of hand with tissue).

Ocular alignment

A positioning of both eyes by the extra ocular muscles so they are targeting the same focal object simultaneously with the result that two images, one from each eye, fall on the respective foveae. The eyes are said to be orthotropic or parallel.

Ocular motility

The ability of the eyes to move together smoothly and fluidly, in all directions, at will.

Ocular tracking

The movement of the eyes together, at will, following a target in any direction. Also termed tracking.

Sensitivity

The ability of a screening to correctly identify those who actually have a disease, health problem, or condition.

Sloan letters chart

A vision acuity chart named after ophthalmologist, Dr. Louise Sloan, composed of ten letters of the Roman alphabet intentionally selected, placed and ordered on the chart. Sloan letters are sans (without) serif and employ uniform fonts in all charts, and for this reason are now the preferred charts.

Specificity

The ability of a screening to correctly identify all those who do not have a disease, health problem, or condition.

Stereopsis

Depth perception or three-dimensionality possible only when both eyes are in alignment and perceive the same image clearly.

Strabismus

A manifest deviation of one or both eyes from the visual axis of the other so they are not simultaneously directed to the same object. (Also referred to as heterotropia or tropia)

Visual acuity

The state, condition or effectiveness of central vision.

Guidelines for Vision Screening in Missouri Schools

APPENDIX E: Glossary

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