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Glossary
Eyewear terms, explained
Short, plain definitions of the words you'll see on product pages and spec sheets. Each one links to a guide when there's more to know.
A
- Acetate frame
- An eyeglass frame made from cellulose acetate, a plastic used in a range of colors and patterns. Read the guide →
- ADD
- Added magnifying power for close-up vision in progressive, bifocal and reading lenses. Read the guide →
- Anti-reflective coating
- A lens coating that reduces reflections and glare. Read the guide →
- Axis
- The angle, from 1 to 180 degrees, of the astigmatism correction. Read the guide →
B
- Base curve
- The curvature of a contact lens, part of a contact lens prescription. Read the guide →
- Bifocal
- A lens with two zones, distance and reading, divided by a visible line. Read the guide →
- Blue-light filter
- A lens treatment or material feature that filters part of the visible blue-light spectrum. Read the guide →
- Bridge width
- The distance between the lenses, the second frame number. Read the guide →
C
- Computer prescription
- A prescription designed for a specific working distance such as a desktop screen. Read the guide →
- Contact lens case
- A container used to store reusable contact lenses in fresh, compatible disinfecting solution. Read the guide →
- Contact lens prescription
- A contact lens fitting record that identifies the prescribed lens and its parameters, such as power, base curve and diameter when appropriate. Read the guide →
- CYL (cylinder)
- Extra lens power that corrects astigmatism. Read the guide →
D
- Daily disposable
- A contact lens worn once and thrown away. Read the guide →
H
- High-index lens
- A lens material with a higher refractive index that can use less material for the same prescription. Read the guide →
I
- Impact-rated eyewear
- Eyewear identified by its maker as meeting a stated impact-protection standard for a particular use. Read the guide →
L
- Lens category
- A 0 to 4 rating of how dark sunglass lenses are. Category 4 is not for driving. Read the guide →
- Lens width
- The first number on a frame (such as 52), the width of one lens in millimeters. Read the guide →
M
- Monel
- A metal alloy used in some eyeglass frames that can contain nickel. Read the guide →
- Multipurpose solution
- An all-in-one care solution used for compatible soft lenses to clean, rinse, disinfect and store them. Read the guide →
O
- OD / OS / OU
- Right eye (OD), left eye (OS) and both eyes (OU) on a prescription. Read the guide →
- Optical center
- The intended point of a lens aligned with the wearer’s eye for the prescribed correction. Read the guide →
P
- PD (pupillary distance)
- The distance between the centers of your pupils, in millimeters, used to center lenses. Read the guide →
- Photochromic lens
- A lens that darkens in UV light outdoors and clears indoors. Read the guide →
- Polarized lens
- A lens that cuts reflected glare from water, roads and snow. Read the guide →
- Polycarbonate
- An impact-resistant, UV-blocking lens material used for kids, sports and safety glasses. Read the guide →
- Prescription safety eyewear
- Protective eyewear that incorporates vision correction or fits over prescription glasses while maintaining the required protective position. Read the guide →
- Prescription sunglasses
- Sunglasses made with corrective lenses matched to an eyeglass prescription. Read the guide →
- Progressive lens
- A no-line lens that changes power gradually from distance to reading. Read the guide →
R
- Refractive index
- A measure of how strongly a lens material bends light; a higher lens index can reduce material thickness for the same prescription. Read the guide →
S
- SPH (sphere)
- The main lens power in diopters. Minus corrects nearsightedness; plus corrects farsightedness. Read the guide →
- Spherical contact lens
- A contact lens with uniform optical power around the lens. Read the guide →
T
- Temple length
- The length of the frame arm, the third frame number. Read the guide →
- Titanium frame
- An eyeglass frame made from titanium or a titanium alloy; check the maker’s exact material description. Read the guide →
- Toric lens
- A contact lens design with different optical powers in different directions to correct astigmatism. Read the guide →
U
- UV protection
- A lens feature that blocks ultraviolet light; lens darkness alone does not establish UV protection. Read the guide →
- UV400
- Lenses that block light up to 400 nm, equal to 100% UVA and UVB protection. Read the guide →