Written and maintained by CASRAI Editorial Board
Last updated
General product information, not medical advice. Which lenses suit you is a decision for your eye care practitioner.
Eyeglass lenses differ in three independent ways: how they correct vision (single vision, bifocal, trifocal, progressive), what they are made of (glass, plastic, polycarbonate, Trivex, high index), and what is added to them (anti-reflective, ultraviolet, photochromic coatings). A pair of glasses combines one choice from each. In the United States a federal rule sits on top of all three: eyeglass lenses must be impact resistant unless a practitioner directs otherwise in writing. This guide sets out the types and then that rule, using the American Academy of Ophthalmology (AAO) and 21 CFR 801.410.
Lens types by vision correction
Single vision
One correction across the whole lens. Our guide to single vision lenses covers what they are in detail.
Bifocal and trifocal
The AAO describes bifocal lenses as correcting for reading on the bottom and for distance on the top. Trifocal glasses have lenses with three different lens corrections, for distance, intermediate and near vision.
Progressive
Progressives have a smooth transition instead of visible dividing lines between zones. The AAO notes two limits: the focused areas are smaller because the transition zones use space, and progressives can cause more distortion than other lens types, which makes them difficult to wear for about 10% of people.
Lens materials
The AAO states that eyeglass lenses used to be made only of glass, but today most are plastic. Plastic lenses are lighter and more flexible than glass, are less likely to shatter, and have inherent ultraviolet (UV) blocking ability.
Polycarbonate, Trivex and high index
- Polycarbonate is highly impact resistant.
- Trivex is a newer plastic material that meets the same safety standards as polycarbonate; its advantage is that it is less distorting than polycarbonate.
- High index lenses are thin, lightweight plastic lenses.
Lens coatings
- Anti-reflective: reduces glare and lets more light pass through the lens.
- Ultraviolet (UV): helps protect the eyes from the sun’s radiation. Some plastic lenses block UV light without a special coating.
- Photochromic: the tint darkens in sunlight and lightens indoors. The AAO lists two drawbacks: they do not work well in cars or airplanes, and in some environments it may take several minutes for the tint to change from dark to light.
Types table
| Type | What it is | Characteristics (per AAO) |
|---|---|---|
| Bifocal | Reading correction at the bottom, distance at the top | Two zones with a visible dividing line |
| Trifocal | Three corrections: distance, intermediate, near | Three zones |
| Progressive | Multifocal with a smooth transition | No visible lines; smaller focus areas; more distortion than other types |
| Plastic | Most common lens material today | Lighter and more flexible than glass; less likely to shatter; inherent UV blocking |
| Polycarbonate | Plastic lens material | Highly impact resistant |
| Trivex | Newer plastic meeting the same safety standards as polycarbonate | Less distorting than polycarbonate |
| High index | Thin, lightweight plastic | Thin and lightweight |
| Anti-reflective coating | Surface coating | Reduces glare |
| Photochromic | Tint changes with light | Does not work well in cars or airplanes; may take several minutes to clear |
The FDA impact-resistance rule
Under 21 CFR 801.410, eyeglasses and sunglasses must be fitted with impact-resistant lenses. The rule does not apply to contact lenses. The test for most lens types is a drop-ball test: a 5/8-inch steel ball weighing about 0.56 ounce is dropped from 50 inches onto the upper surface of the lens, striking within a 5/8-inch circle at the geometric center. A lens fails if it fractures, meaning it cracks through its entire thickness, or if material visible to the naked eye detaches from the surface facing the eye.
Exemptions and records
- A physician or optometrist may find that impact-resistant lenses will not fulfil the visual requirements of a particular patient. The practitioner must then direct the use of other lenses in writing and give written notice to the patient.
- Prism segment multifocal, slab-off prism and lenticular cataract lenses must be impact resistant but need not be subjected to the impact test.
- Records of sales and distribution, such as invoices, must be kept for three years.
Lens rules and characteristics by setting
| Topic | What the sources say | Source |
|---|---|---|
| Eyeglasses dispensed in any setting (clinic, hospital, lab) | Lenses must be impact resistant unless the practitioner directs otherwise in writing | 21 CFR 801.410 |
| Polycarbonate | Highly impact resistant | AAO |
| High index | Thin, lightweight plastic lenses | AAO |
| Trivex vs polycarbonate | Trivex meets the same safety standards and is less distorting | AAO |
| Cars and airplanes | Photochromic lenses do not work well there | AAO |
Eyewear worn specifically against workplace hazards is a separate topic; see prescription safety glasses and ANSI Z87.1. For the lens in the context of the whole frame, see parts of eyeglasses, and for tinted lenses see types of sunglasses. Clinics stocking eyewear supplies can start from the optometry clinic supply checklist.
What to check on the order
21 CFR 801.410 requires impact-resistant lenses, so a pair that is not impact resistant should come with the practitioner’s written direction and written notice to the patient. An order or invoice normally identifies the correction type (single vision, bifocal, trifocal or progressive), the material, and each coating. Because some plastic lenses already block UV, a UV coating may or may not be a separate item depending on the material.
FAQ
What are the main types of eyeglass lenses?
By vision correction: single vision, bifocal, trifocal and progressive. By material: glass and plastic, including polycarbonate, Trivex and high index. By coating: anti-reflective, UV and photochromic.
What are the types of prescription lenses?
Single vision lenses carry one correction; bifocal, trifocal and progressive lenses are multifocal, combining corrections for different distances in one lens.
What are eyeglass lens materials?
Lenses were once made only of glass, but most today are plastic. Polycarbonate, Trivex and high index are plastics with different properties, listed in the table above.
What are eyeglass lens coatings?
The AAO describes anti-reflective, ultraviolet and photochromic coatings, with the characteristics listed above.
Do eyeglass lenses have to be impact resistant?
In the United States, yes, under 21 CFR 801.410, except where a practitioner finds impact-resistant lenses will not meet the patient’s visual requirements and directs other lenses in writing.
Sources
- American Academy of Ophthalmology, Eyeglasses: How to Choose Glasses, checked 2026-10-30.
- U.S. Food and Drug Administration, 21 CFR 801.410, Use of impact-resistant lenses in eyeglasses and sunglasses, checked 2026-10-30.
