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Glossary

Accommodation

A process when our eyes need to change focus in order to see clearly at near.

Amblyopia

An eye disorder characterized by an impaired vision in an eye without apparent internal or external organic defects. In amblyopia, visual stimulation either fails to transmit or is poorly transmitted through the optic nerve to the brain for a continuous period of time which leads to poor vision.

Astigmatism

A refractive error of the eye in which parallel rays of light from an external source do not converge on a single focal point on the retina.

Computer Vision Syndrome (CVS)

A term to describe these eye problems, and may affect up to 90% of computer users, whose symptoms may include asthenopia (eyestrain), headaches, dry eye, diplopia (double vision) and blurred vision after prolonged use (>1 hour) of computer or other digital screen devices.

Concave lens

A concave lens is thinner at its centre than at its edges, and is used to correct short-sightedness (myopia).

Convergence

The simultaneous inward movement of both eyes toward each other, usually in an effort to maintain single binocular vision when viewing an object.

Convex Lens

A convex lens is bigger at its centre in comparison to its edges and is applied in correcting long-sightedness (hyperopia).

Cornea

The transparent anterior part of the external coat of the eye covering the iris and the pupil and continuous with the sclera.

Dry eye

An eye disease caused by eye dryness, which in turn, is caused by either decreased tear production or increased tear film evaporation.

Esotropia

Strabismus in which one eye deviates inward.

Exotropia

Strabismus in which one eyes turn outward.

Farsightedness

Seeing objects at a distance more clearly than those near at hand; hyperopic.

Hyperopia

Same as Farsightedness. Seeing objects at a distance more clearly than those near at hand; hyperopic.

Hypertropia

Upward deviation of the visual axis of one eye.

Hypotropia

Downward deviation of the visual axis of one eye.

Iris

A thin, circular structure in the eye, responsible for controlling the diameter and size of the pupil and thus the amount of light reaching the retina.

Lazy eye

Same as Amblyopia. An eye disorder characterized by an impaired vision in an eye without apparent internal or external organic defects. In amblyopia, visual stimulation either fails to transmit or is poorly transmitted through the optic nerve to the brain for a continuous period of time which leads to poor vision.

Lens

A transparent, biconvex structure in the eye that, along with the cornea, helps to refract light to be focused on the retina.

Macular

An oval-shaped highly pigmented yellow spot near the centre of the retina of the human eye.

Myopia

Same as Nearsightedness. Seeing distinctly at a short distance only; myopic.

Nearsightedness

Seeing distinctly at a short distance only; myopic.

Optic Nerve

Nerve that transmits visual information from the retina to the brain.

Photoreceptors

Photosensitive cells in the retina stimulated by light.

Pupil

A hole located in the centre of the iris of the eye that allows light to enter the retina.

Refractive Errors

This is an error in the focusing of light by the eye and a frequent reason for reduced visual acuity.

Retina

The innermost coat of the posterior part of the eyeball that receives the image produced by the lens, is continuous with the optic nerve, and consists of several layers, one of which contains the rods and cones (photoreceptors) that are sensitive to light.

Strabismus

A disorder of vision due to a deviation from normal orientation of one or both eyes so that both cannot be directed at the same object at the same time; squint; crossed eyes.

Visual Cortex

The portion of the cerebral cortex of the brain that receives and processes impulses from the optic nerves.