CLINICAL

  OPTICAL

CLEARING UP LENS COATINGS

AR COATINGS CAN HELP PROTECT AGAINST HARMFUL RAYS

DAVE ZIEGLER, O.D.

Q: DO ALL AR COATINGS HAVE UV PROTECTION?

A: While an AR coating can reflect about 25% to 50% of UV light, according to Pete Hanlin, director of technical marketing at Essilor, most of the protection comes from the property of the lens material to absorb UV light. A significant amount of UV light can reach the eyes from the back surface of the lens due to backside reflection. To prevent this, coatings have been engineered to prevent back-surface reflection. Instead, UV light passes through the coating to be absorbed in the lens material. This can reduce the patient’s overall exposure to UV light by 50%.

Q: ARE BLUE-BLOCKING LENSES EFFECTIVE?

A: Yes. Research has linked high-energy blue-violet light to the accumulation of lipofuscin in the macula, which can lead to macular degeneration. There is a very small band of wavelengths to which this is attributed; they happen to be in close proximity to the blue light that controls circadian rhythms. Therefore, it would be crucial to allow the beneficial blue light to pass through the lens, while also attenuating the harmful blue light.

The two ways to eliminate a particular wavelength are reflection or absorption. By varying the composition of the multi-layered AR stack, just the harmful blue-violet light is reflected away from the lens. This is why the new blue-blocking AR coatings have a characteristic blue color when incident light reflects off the lens at the right angle.

Blue Light is defined as visible light between 380 nm and 500 nm. It can be further broken down to blue-violet light, at 380 nm to 450 nm, and blue-turquoise light, from 450 to 500 nm, according to AllAboutVision.com.

The current blue-blocking AR coatings reflect about 20% of the harmful blue light from entering the eyes, according to Mr. Hanlin. Whether that is enough to effectively reduce the likelihood of AMD is unknown, but it clearly helps to some degree. You could liken it to wearing SPF20 sunscreen when outdoors. It may not prevent skin cancer, but it helps lower the risk. Watch for new modified lens materials, which selectively absorb the harmful blue light, to augment the AR coating to improve the overall effectiveness of blue-blocking lenses.

Q: DO POLARIZED LENSES BLOCK BLUE LIGHT?

A: While a lot of attention has been given to the blue light produced by electronic devices and modern lighting, the primary source of harmful blue light is the sun, which produces 200 to 500 times more blue-violet light than an electronic screen, according to Mr. Hanlin.

Polarized sunglasses reduce exposure to harmful blue light by 87% to 92%, and are a crucial part of protection from harmful blue light. OM

Pete Hanlin of Essilor helped in the writing this column.

Questions are based on reader responses to an Optometric Management online survey, which closed on Dec. 20.

DR. ZIEGLER is a senior partner at Ziegler & Leffingwell Eyecare in Milwaukee, Wisc., and a fellow of the American Academy of Optometry. Email him at daveaziegler@gmail.com, or visit tinyurl.com/OMcomment to comment.