Impact Resistance of Lens Materials

by Dick
(Ames, Iowa)

Q: I've worn polycarbonate lenses for many years because of a strong prescription (-6.5/ -7.5). The impact resistance is a welcome side effect.

Now I am buying these plastic lenses more because they are aspheric than because of refraction index 1.61 or abbe number. How does the impact resistance compare with polycarbonate?

A: First of all the refractive index have nothing to do with the impact resistance, it only affects the thickness and weight of the lens.

As you can see at the lenses materials section, the most used lenses are made of plastic, polycarbonate or trivex.

The polycarbonate and trivex are the most resistant materials. They are specially made for withstand to scratches and breaking. If you will compare these materials (polycarbonate and trivex) with the plastic all having the same index (thickness), the polycarbonate and trivex are the best, the most resistant.

You say you have a large minus (-) diopter, meaning the lens is thin in the middle and thick on the edge, so we can say that the most sensitive part of the lens is in the middle, on the centre of the lens.

If you choose a high index lens, all of it will be thinner at the center and edge, so more sensitive to scratches and breaking. The high index does not provide additional impact resistance, it depends only on the material. So I suggest you to use the same polycarbonate you had before, that offers the most protection for your lenses.

If you will use another material, less resistant, take extra care of your lenses, wipe only with microfiber cloth as shown here, and try to keep them out of dust, chemicals or any other harming shocks.

Also, it is a good idea to have protection coatings like hardening on the lenses, no matter what kind of material they are made from. Any extra protection is always welcome.

More about lens materials

Eyeglass Lens Materials

High Index Lenses

Arpi

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