Photochromic lenses: Transitions and other light-adaptive lenses

Photochromic lenses are eyeglass lenses that are clear (or nearly clear) indoors and darken automatically when exposed to sunlight. Other terms sometimes used for photochromic lenses include "light-adaptive lenses" and "variable tint lenses."
The most popular brand of photochromic lenses sold in the United States are Transitions Lenses  (Transitions Optical). Because of this, some people — including some eye care practitioners

— refer to photochromic lenses as "transitions lenses" or "transition lenses." But there are other brands of photochromic lenses available as well.The molecules responsible for causing photochromic lenses to darken are activated by the sun's ultraviolet radiation. Because UV rays penetrate clouds, photochromic lenses will darken on overcast days as well as sunny days.
Photochromic lenses typically will not darken inside a vehicle because the windshield glass blocks most UV rays. Recent advancements in technology allow some photochromic lenses to activate with both UV and visible light, providing some darkening behind the windshield. Ask your optician for details.
Photochromic lenses are available in nearly all lens materials and designs, including high-index lenses, bifocals and progressive lenses. An added benefit of photochromic lenses is that they shield your eyes from 100 percent of the sun's harmful UVA and UVB rays.
Because a person's lifetime exposure to sunlight and UV radiation has been associated with cataracts later in life, it's a good idea to consider photochromic lenses for children's eyewear as well as for eyeglasses for adults. Polycarbonate is the safest lens material for kids, providing up to 10 times the impact resistance of other lens materials.

Adding anti-reflective coating to photochromic lenses enhances their performance even further. AR coating allows more light to pass through photochromic lenses for sharper vision in low-light conditions (such as driving at night), and eliminates bothersome reflections of sunlight and other light from the backside of the lenses in bright conditions.
Though photochromic lenses cost more than clear eyeglass lenses, they offer the convenience of reducing the need to carry a pair of prescription sunglasses with you everywhere you go.

Photochromic sunglasses

Photochromic sunglasses are primarily for outdoor wear. They are not as clear indoors as other photochromic lenses, but they provide extra comfort in bright sunlight and behind the wheel.
Transitions Drivewear (Transitions Optical and Younger Optics) — These polarized adaptive lenses are designed specifically for the driving task. They adapt to changing light conditions when worn inside a vehicle, enhance contrast, and improve visual performance for driving, according to Transitions Optical.
Transitions Optical also has incorporated the company's photochromic technology into a line of adaptive sunglasses, motorcycle and bike helmet shields and snow goggles. These products enhance visual performance during outdoor activities by providing comfort in changing light conditions, enhancing contrast and offering the convenience of not having to switch products as light changes, according to the company.
Transitions Optical's photochromic technology is available in products from leading brands like Bell Helmets, Shoei, Oakley, Nike and Dragon Alliance in a variety of tint and color options, including clear to dark lenses, dark to darker lenses, and clear to dark helmet shields. Also, the photochromic performance of products made for snowboarding and other winter activities is optimized for cold temperatures, according to the company.

Photochromic lenses and blue light

Besides protecting your eyes from glare outdoors, photochromic lenses offer an additional important benefit — they help protect your eyes from harmful blue light.
Blue light contributes to digital eye strain and causes oxidative stress in the retina. It's even possible that long-term exposure to harmful blue light from sunlight and the display screens of computers, smartphones and other digital devices may increase a person's risk of macular degeneration and other eye problems later in life.
Photochromic lenses can help. For example:

• Transitions Signature photochromic lenses block 1.4 times more harmful blue light indoors than basic clear lenses, and they filter over 8 times more harmful blue light outdoors than clear lenses.
• Transitions Vantage photochromic lenses filter at least 2 times more harmful blue light indoors than clear lenses, and they block over 6 times more blue light outdoors than clear lenses.
• Transitions XTRActive photochromic lenses block at least 2 times more harmful blue light indoors than clear lenses, and 8 times more harmful blue light outdoors.