a. Single Vision Lens. A single vision lens is a spectacle lens having the same focal power throughout its useful area, for reading, intermediate or distant vision.
b. Bifocal Lens. A bifocal lens is a spectacle lens of two portions whose focal powers differ from each other. Usually the upper portion is larger and is for distant vision, and the lower portion is smaller and is for near vision.
c. Trifocal Lens. A trifocal lens is a multifocal lens of three portions whose focal powers differ from each other. Usually the top portion is the largest and is for distant vision, the middle for intermediate distances, and the bottom for near vision.
d. Progressive Addition Lens. A progressive addition lens is a multifocal lens having a progressive increase in positive power from the distance-seeing portion to the near-seeing portion.
e. Tinted Lens. A tinted lens is a lens with color absorption properties designed to reduce light transmission and/or selectively absorb undesirable incident radiations, such as ultraviolet (UV) radiation, etc. In contact lenses, the color may be also for facilitating location.
f. Photochromic Lens. A photochromic lens is a lens with substances which change in color and in light transmission properties upon exposure to a change in light intensity or to UV radiation. The change may, or may not, be reversible.
g. Coating, Lens. A lens coating is a thin deposit of a metallic salt, such as magnesium fluoride, about one-fourth as thick as a wavelength of light, applied to a surface of a lens to reduce, by interference, the amount of light reflected, and, if combined with a coloring ingredient, to reduce light transmission, and, to impart scratch resistance.
h. Prismatic Lens. A prismatic lens is a lens with prism power that deviates the path of light.
i. Lenticular Lens. A lenticular lens is an ophthalmic or spectacle lens of high dioptric power with the prescription ground only in the central portion, the peripheral (usually a focal) portion of the lens serving only to give dimensions suitable for mounting in a spectacle, permitting a reduced center thickness in the case of convex lenses and a reduced edge thickness in the case of concave lenses.
j. Aspherical Lens. An aspherical lens is a lens in which one or both surfaces in the central sagittal section do not describe a circle, usually conforming instead to a parabola or some similar curve systematically deviant from a circle from the center to the periphery of the lens, so designed to correct for or reduce certain types of aberrations.
k. Balance Lens. A balance lens is a spectacle lens of undesignated power serving only to balance the weight and the appearance of its mate in front of the other eye.
l. Bridge. The bridge is that part of a spectacle front which connects the two eye wires, the lens arms, or the nasal straps. Its name stems from the early type of saddle bridge which rested on the bridge of the nose.
m. Temple. A temple is one of a pair of shafts extending backward from the end pieces of a spectacle frame or mounting to rest against the head or the ears for the purpose of holding the frame or mounting in position.
n. Low-vision Device. A low-vision device is a special aid, appliance, or technique used to improve the vision or functional rehabilitation ability of a beneficiary with subnormal vision.
o. Subnormal Vision. Subnormal vision is vision considered being inferior to normal vision, as represented by accepted standards of visual acuity, field of vision, or motility, and uncorrectable by conventional lenses, or the branch of visual care identified with its correction or rehabilitation or special aids or techniques.
p. Safety Spectacles. Safety spectacles are the result of the combination of frames and lenses that meet American National Standards Institute Z80 safety standards to provide protection to the eyes, especially from injury due to impact.
q. Polycarbonate. Polycarbonate is a transparent material consisting of thermoplastic linear polyesters of carbonic acid, made by the polymeric condensation of bisphenols with a phosgene or its derivatives and used for injection molding of certain ophthalmic lenses.
r. Photophobia. Photophobia is an abnormal intolerance or fear of light.
s. Photosensitivity. Photosensitivity is the capacity of the cells of an organ or an organism to be stimulated to activity by light; it is also the property of certain chemicals to react to light.
t. Enucleation. Enucleation is the removal of a whole tumor or an entire organ, as in the removal of the eye from its socket.
u. Evisceration of the Eye. Evisceration of the eye is the surgical removal of the inner contents of the eye, the sclera being left intact.
v. American National Standards Institute (ANSI) Accredited Committee Z80 for Ophthalmic Standards. The ANSI Accredited Committee Z80 for Ophthalmic Standards is the nationally-recognized organization that establishes standards that apply to:
(1) Ophthalmic lenses, equipment, instruments, and processes used in the final fabrication level which affects the relationship to ophthalmic frames, sunglasses, and fashion eyewear;
(2) Contact lenses and accessories for their use;
(3) Intraocular implant lenses, low-vision devices, and ophthalmic contact devices; and
(4) Optical instrumentation used in ophthalmic procedures and vision evaluation.
NOTE: Standards established by the ANSI Z80 Committee do not apply to industrial safety devices, or to procedures used in clinical ophthalmic examinations.