Do photochromic lenses prevent cataract?

When exposed to UV and/or sunlight photochromic lenses go darker than when in the clear state.

Photochromic lenses absorb UV light and exposure to UV light has been linked to cataract development. So, in theory, reducing the amount of UV hitting the crystalline lens should slow down the development of cataract.

Short-wavelength blue light which occurs in the visible spectrum may also be part of the cataract formation process. When a photochromic lens is dark it will reduce the amount of light (all wavelengths) going into the eye and hitting the crystalline lens.

Therefore, in the darkened state less blue light hits the crystalline lens. Again, in theory, reducing the amount of blue light hitting the crystalline lens should slow down the development of cataract.

People who have small to moderate amounts of cataracts (not enough to warrant surgery) often suffer from glare caused by the cataractous material. When outside, reducing the amount of sun light will help reduce glare and improve eye visual comfort.