American Board of Ophthalmology (ABO) Practice Exam

Which type of lens can automatically darken in sunlight?

1. Standard lens

2. Photochromic lens

3. Progressive lens

4. Single-vision lens

The correct answer is: Photochromic lens

Photochromic lenses are designed to automatically darken in response to UV light exposure, specifically sunlight. This phenomenon occurs because the lens material contains special molecules that undergo a chemical reaction when exposed to ultraviolet (UV) radiation, causing the lenses to tint and reduce glare. When the lenses are no longer exposed to UV light, they revert to their clear state. This adaptive feature provides convenience for wearers, eliminating the need to switch between regular glasses and sunglasses when transitioning between indoor and outdoor environments. In contrast, standard lenses do not have this ability to change tint and remain clear regardless of lighting conditions. Progressive lenses, which provide a gradient of vision correction, are available with photochromic options but are not inherently designed for light adaptation on their own. Similarly, single-vision lenses, like standard lenses, do not provide the photochromic functionality unless specifically manufactured as such. Therefore, the correct answer is photochromic lenses due to their unique capability to respond dynamically to changing light conditions.