Welcome to a near-perfect pair of glasses.
New lightweight plastic photochromatic lenses are able to change from light to dark tint in just a moment. These lenses lighten to about a 10% tint and darken to a 80% tint when exposed to the UV rays of the sun. Now many patients can avoid the trouble of having two pairs of glasses while still taking advantage of virtually all lens designs such as invisible bifocals, thin lenses, etc. and still have the UV protection of prescription sun glasses all in one pair.
That means healthy sight for just about everyone, anywhere, anytime!