Focus on Fundamentals

This installment of EB’s back-to-basics series focuses on the science that transforms photochromic lenses, the benefits they can provide to patients, and how versatile they are when it comes to materials and styling.

Photochromic lenses change from a clear to a darkened, tinted state of saturation when exposed to ultraviolet light.

What actually transpires within the lens in order to achieve this reaction is a modern marvel of lens technology, science, and what seems like a bit of magic.

Photochromic lenses are made of billions of nano-size molecules that are invisible to the human eye, causing no effect on visual clarity or the prescription built into the lenses. When the lenses are exposed to ultraviolet light, the molecules undergo a chemical reaction, causing a structural change that results in an activated photochromic lens with a darkened appearance.

The Science

How photochromic lenses change from light to dark for the wearer can be broken down into four steps of activation and reversal.

1. Exposure and absorption of UV light. When exposed to UV light, the photochromic molecules embedded in the lens material absorb the energy emitted from the UV light source, whether natural or artificial.
2. Chemical reaction and molecular transformation. The absorbed energy triggers a chemical reaction within the molecules, causing the molecules to change their structure.
3. Cosmetic change. Due to the molecules changing structure, they absorb more light, resulting in the darkening of the lens. The saturation varies depending on the amount of UV light the lens has been exposed to.
4. Reversal. When the UV light source is diminished, the photochromic molecules gradually revert to their original state, and the lens becomes fully clear again.

 

 

NOT YOUR GRANDPA’S PHOTOCHROMICS.

Beyond the vision and eye health benefits, photochromic lenses offer opportunities for styling with a rainbow of lens colors to choose from. Gray and brown aren’t the only options anymore—choose from electric blues, earthy greens, vivacious purples, warm yellows, ravishing reds, and playful pink tones.

Photochromic lenses are also available in a variety of types to meet different visual and situational needs. Polarized photochromic lenses offer additional glare reduction in the activated state, and Xtractive or Extra Dark photochromic lenses activate to level three, the darkest sunglass tint, outdoors, even in very hot temperatures.

The Benefits

The benefits of photochromic lenses are plentiful, and with a foundational understanding of how they work, explaining their advantages is easy.

1. UV and blue light protection. Most photochromic lenses offer up to UV400 protection, though this varies by brand, and some styles offer additional blue light protection, shielding eyes from harmful ultraviolet rays that can contribute to cataracts and other eye health-related conditions.
2. A solution to light sensitivity. Photochromic lenses are highly responsive to ultraviolet light and quickly adjust to changing light conditions. This feature provides shading in various environmental situations, including those bright overcast days that can bother light-sensitive patients.
3. Convenience. Not only do photochromic lenses protect wearers from sudden exposure to bright sunlight, but they also take away the need to carry multiple pairs and frequently switch back and forth when traveling between indoor and outdoor settings.
4. Visual comfort and acuity. Photochromic lenses reduce excessive brightness, glare, and reflective light, thus enhancing visual comfort by easing eye strain and eliminating the need to squint.
5. Product availability and photochromic lens style versatility. There doesn’t need to be any compromise on lens style to select a photochromic lens feature: 1.5, 1.6, 1.67, 1.74, Trivex, Poly, Airwear, and even glass are available with a photochromic feature. Photochromic lenses are also available in single-vision, progressives, bifocals, and even occupational lens layouts, making them a suitable option for people with different vision needs.