American Board of Opticianry (ABO) Practice Test 2025 - Free ABO Practice Questions and Study Guide

Photochromic lenses are best known for their ability to darken in sunlight and return to clear indoors. This unique characteristic allows them to adapt to changing light conditions, providing convenience for the wearer. When exposed to UV light from the sun, the lenses undergo a chemical reaction that causes them to darken, effectively blocking harmful rays and reducing glare. Once the wearer moves indoors, where UV light is limited, the lenses quickly transition back to their clear state, offering unobstructed vision without the need to switch between prescription glasses and sunglasses.

While there are benefits associated with the other options, they do not define the primary function of photochromic lenses. For example, remaining tinted indoors is not a feature of photochromic lenses; instead, they are designed to clear up as the light changes. Although they can be lighter than some regular lenses, that is not their distinguishing feature. Scratch resistance can be a property of various lenses but does not specifically relate to the photochromic technology itself.