Dictionary of terms relating to
eyesight and vision

A - B - C - D - E - F - G - H - I - K - L
M - N - O - P - R - S - T - V - W - Y

dictionary icon


The most sensitive part of the retina that is about the size of a pinhead and is where our most detailed vision occurs. (See diagram of the eye)

Macular Degeneration

A deterioration of the central portion of the retina known as the macula.


A voluntary or intentional reduction in visual acuity or other examination data.


Also called microtropia, monofixation syndrome, and small angle strabismus. A small angle deviation (inward or outward, commonly inward) that is less than five degrees with some amount of stereopsis (depth perception) and anomalous retinal correspondence (ARC). Possible mild amblyopia, eccentric fixation, and/or anisometropia may also be present. It frequently results from the treatment of a larger-angle deviation (esotropia or exotropia) by optical correction, vision therapy, pharmacological agents, and/or extraocular muscle surgery. Treatment for microstrabimus consists mostly of correcting significant refractive errors and any coexisting amblyopia. The use of vision therapy and prisms to establish bifoveal fusion has been successful in selected cases.

Minus (-) Lens

Concave lens, stimulates focusing and diverges light. The lens is thinner in the center than the edges. It is used in glasses or contact lenses for people who are nearsighted (myopia).


Miotics are topical eye medications that cause the pupil to contract, which helps to open the eye's drainage system and allows the aqueous humor (the fluid that causes the increased pressure in the eye) to drain out of the eye. The incidence of side effects and multiple daily dosing may prohibit the use of miotics.

Monocular Vision

Only one eye having useful vision.

Morning glory syndrome

A birth defect of the optic nerve (the nerve to the eye) in which there is a coloboma (cleft) of the optic disc. The coloboma results in a funnel-shaped optic nerve head with a white dot in the center, an elevated ring of pigment around the disk, and vessels radiating out from the ring like spokes. Reflection from within the eye may give the appearance of a white pupil. Vision in the affected eye is severely impaired. There is an increased risk of retinal detachment. Also called morning glory anomaly.


Nearsightedness, an individual will have difficulty seeing clearly at distance. Light entering the eye focuses in front of the retina when the eye is at rest and is corrected with a minus lens. A condition known as high myopia occurs when myopia is greater than 6 diopters. Typically, vision therapy is not prescribed for myopia. More information .