Tendency of one eye to deviate upward.


An actual deviation of the z-axes in the vertical meridian.


Vertical heterophora in which one eye tends to deviate downwards relative to the other. This can be differentiated from Hyperphoria in the other eye only by evidence of paresis or paralysis of elevating.


Lens that is resistant to shattering or splintering. Polycarbonate is the most impact resistant lens material making it very safe to wear.

Intermediate Examination

Describes a level of service pertaining to the evaluation of a new or existing condition complicated with a new diagnostic or management problem. This does not necessarily relate to the primary diagnosis. It includes history, general medical observation, external ocular and adnexal examination and other diagnostic procedures as indicated; it may include the use of mydriasis.

Intermediate-vision Lenses

That area in a trifocal lens or lens blank that has been designed to correct vision at intermediate to distant ranges.


Within the eye.


Colored part of eye.


Inflamed cornea.


A condition (cause unknown) in which the cornea gets progressively steeper (cone-shaped). Fitting with a hard contact lens may slow progression. Surgery may eventually be necessary.


An instrument used to measure the curvature of small areas of the cornea by reflected light.


Acronym: Laser in Situ Keratomileusis. Type of refractive surgery in which the cornea is reshaped to change its optical power.


A transparent medium bounded by two geometrically defined surfaces, one of which is curved that is, spherical, cylindrical, toroidal or aspheric.

Lens Size

The horizontal box dimension (A-dimension) of a finished lens. Also called eye size.

Lens, Corrected Curve

A lens designed to reduce peripheral power errors for the conditions of intended use over a specified portion of the field of view.

Lens, Digital Single Vision

Single vision is a lens that corrects one aspect of the wearer’s vision. The digital version goes through a process in which a lens is manufactured with less overall distortion and aberration as found with traditionally surfaced lenses. Progressives can also be manufactured as digital.

Lens, Glass Photochromic

Lens that changes to a cosmetic sunglass in the direct sunlight.

Lens, HD Progressive

Commonly referred to as free-form lenses, this new optimized lens design offers the latest in progressive lens technology and is ideal for people with specific visual needs. This includes those who are new to progressives and needing them for the first time. Also suitable for those motivated to wear progressive lenses, but have had issues adapting to them in the past, as well as current progressive wearers interested in the latest technology.

Lens, Lenticular

A lens, usually of strong refractive power, in which the prescribed power is applied over only a limited central region of the lens, called the lenticular portion. The remainder of the lens, called the carrier, provides no refractive correction but gives dimension to the lens to allow for mounting in a spectacle frame.

Lens, Lined Bifocal

A lens designed for two viewing ranges. The upper part of the lens is used for distance vision and the lower part of the lens is used for near vision.