The property of some optical lenses or systems of projecting a real inverted image of an object that is of a larger area than the object itself.

Low Vision Aids

Low-vision aids are devices designed to improve visual performance and can improve academic and social situations (among others).

Low Vision

Term usually used to indicate vision of less than 20/20.


A form of energy necessary to see. Visible light is that part of the spectrum that produces sensation of sight in the human eye. The radiation wavelengths in this visible range are very small and are usually expressed in either millimicrons or nanometers. The values given for the limits of the visible- light wavelength range depend on the textbook you are reading, but are around 380-760 nanometers or 400-750 nanometers. The rays that cause us to see violet have the smaller, shorter wavelength, around 380 nanometers or millimicrons. Each color of the spectrum – blue, green, yellow and orange – have a range of wavelengths. Red has the highest range, at around 660-750 nanometers.

Lenticular Lens

See Lens, Lenticular.


Instrument that can measure the power of a spectacle lens.

Lens, Uncut

A lens with finished optical surfaces on both sides but not edged for mounting in a frame.

Lens, Trifocal

A multifocal lens with three different powers in three different positions. Usually, the top (largest) portion is for distance vision, the middle portion is for intermediate distances and the bottom portion is for near vision.

Lens, Toric

A lens that has two distinct curvatures at right angles (90 degrees) to each other. See Lens, Sphero-Cylinder.

Lens, Stock Factory Finished Uncut

A lens supplied by a manufacturer with both surfaces finished and a specific back vertex power or powers. Such a lens has yet to be edged to a specific shape.

Lens, Sphero-cylinder

A lens that has different refractive power in the two principal meridians. It is sometimes referred to as an astigmatic or toric lens. It is sometimes incorrectly referred to as a cylinder lens.

Lens, Spherical

A lens that has the same refractive power in all meridians. Such a lens may have rotationally symmetrical aspheric surfaces.

Lens, Specialty (Myodisc, Lenticular Grind, Double Sided Grind)

  • Myo-disc: A lens that will correct high myopia. Grinded on both sides to reduce thickness.
  • Lenticular: A lens that will correct high hyperopia. Essentially a lens within a carrier lens to reduce thickness
  • Double Grind: also called myo-disc (see above)

Lens Size

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

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, Single Vision

A lens with one correction, either for distance vision or for near vision, as opposed to a bifocal lens, which has corrections, for both near and distance vision.

Lens, Semi-finished

A lens that has only one surface finished.

Lens, Progressive

Progressive addition lenses (PAL) provide continuous progression of lens powers between multifocal lenses, resulting in many lens powers to facilitate all viewing distances without the visible line of bifocal or trifocal lenses. They are categorized in the following groups within the Davis Vision formulary, which includes many popular brand names and the latest technology:

  • Standard tier
    • Available in traditional designs
    • Wide reading areas with a smooth progression from the distance viewing area down to the reading area of the lens
  • Premium tier
    • Available in both traditional and digital designs
    • Wider fields of vision in the distance and reading viewing areas versus stand progressive designs
  • Ultra tier
    • Every design is digitally surfaced
    • Greater enhanced visual clarity
  • Ultimate tier
    • Best in digital design and cutting edge technology
    • Widest viewing areas for both distance and reading, and every distance in-between

Lens, Polycarbonate

Polycarbonate lenses are comprised of a lightweight impact-resistant material and are used where eye safety is a concern. Additionally, Polycarbonate lenses provide protection from the sun’s UV rays. Popular uses include safety eyewear, sports protective eyewear and children’s eyeglasses.

  • Children: Polycarbonate lenses are covered in full (no copayment) for dependent children.
  • Adults: Polycarbonate lenses are covered for adults if they are monocular patients and patients with prescriptions +/- 6.00 diopters or greater.
    • Monocular patients see out of one eye.
    • A diopter is a unit of measurement of the optical power of the lens. Convex lenses have positive value (+1.00 to +3.00 for example) and are used to correct farsightedness. Concave lenses have negative value (1.00 to 3.00 for example) and are used to correct nearsightedness. Optometrists usually measure refractive error using lenses graded in steps of 0.25 diopters.

Lens, Polarized

Polarized lenses are used in sunglasses and provide wearers with a filter to eliminate the horizontal glare experienced from reflective surfaces, such as water or the road’s surface. Polarized lenses are also capable of being worn indoors to protect light-sensitive individuals from light exposure. These lenses are recommended for patients with eye conditions such as cataracts and age related macular degeneration.

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