Photochromic lenses are clear indoors and darken when they are exposed to sunlight. They shield eyes from exposure to glare and potentially damaging UV rays. Photochromic features can be added to prescription eyeglasses, but they raise the cost of the lenses. Fortunately, photochromic lenses are at least partially covered by many vision benefits plans, but the amount will depend on the plan, your eye condition and type of photochromic lenses and eyeglasses you choose.