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Lens Materials

In the beginning, all lenses were made from glass.  However, glass lenses, even safety tempered glass, carry a higher risk of injury due to shattering from impact.  For this reason, we do not offer glass lenses to our patients as there are safer and better alternatives. 

When evaluating lens materials, there are typically five factors that eyeglass wearers to consider:  thinness of the lenses, amount of color distortion, weight, ultraviolet protection, and strength/impact resistance of  the material.

The thinness of a lens material is characterized by its index of refraction or the amount light bends.  A higher index of refraction for a lens material means it will be thinner for the same prescription than a lower index of refraction.

Certain lens materials distort colors more than others.  A large amount of color distortion or chromatic aberration are ideal for diamonds which sparkle many colors but not ideal for color true vision.  Color true vision helps to see objects in their real hues.

Different lens materials will have different weights even when the lenses are identical in prescription and lens diameter much like a box of feathers versus a box of bricks of the same volume.

Lens materials can filter or allow different amounts of ultraviolet rays from the sun.  Large amounts of ultraviolet A rays are considered harmful to eyes and are known to contribute to age related cataracts.

The strength of the lenses is important especially for those who might need eye protection against projectiles and chemicals. A stronger lens material could help in situations where your eyewear and eyes are at risk for impact (e.g. racquetball, volleyball, bicycle riding, working in a laboratory).  These lenses are strongly recommended for children and those with one good eye.

Below we list some of the lens materials we offer for our eyewear with some pros and cons for each.

Plastic CR-39, Index of Refraction=1.50
Pros:
Lowest cost. Excellent chromatic vision properties.
Cons: Allows over 10% ultraviolet A. One of the weaker materials. Weight is heavier due to greater thickness.

Polycarbonate, Index of Refraction=1.59
Pros:
Low cost. Thin Lens. Very Strong Impact Protection. 100% UVA protection.
Cons:
Prone to chromatic distortions especially in high prescriptions.

Phoenix/Trivex Index of Refraction=1.53
Pros:
Low cost. Very Strong Impact Protection. 100% UVA protection. Very Good chromatic vision properties.
Cons:
Not as thin as other materials.

EYRY, Index of Refraction=1.70
Pros:
One of thinnest plastic materials. Strong Impact Protection. 100% UVA protection. Good chromatic vision properties.
Cons:
High Cost.

419 Eccles Ave. South San Francisco, CA 94080
Tel: (650) 873-1089, Monday-Friday 11:00AM to 5:00PM