The Technical Side of Photochromic & AR Technology

A primer on what you really need to know about photochromic and AR technology

By Karlen McLean, ABOC, NCLC

Why does knowing the technical aspect of photochromic and anti-reflective (AR), also known as No-Glare, technology matter to dispensing ECPs? Can't you just recommend and sell on features and benefits alone? Yes, that's true in many cases, but in others it pays to have in-depth knowledge of the product you dispense, for example, to be able to expertly back up or debunk a polarized or AR myth, or to help troubleshoot a job.

Some folks enjoy, even thrive on, reading white papers. But many of you probably don't have the access or time-frame to do it. So we did the work for you and condensed white paper knowledge into this succinct primer on what you really need to know about photochromic and anti-reflection technology.

INTEGRATION

Integration is the key word with photochromic and AR technology. Just like hard-and-scratch coatings are an integral component of the attributes and success of AR—AR durability isn't achieved without a solid coating layer—so, too, photochromics and AR work better together to cut glare, delivering the clearest, most adaptable vision for the wearer (see the benefits sidebar).

To cut the most glare, in addition to photochromic properties, anti-reflection (AR) technology is a lens must. Some manufacturers advocate applying AR to both sides of a lens in order to cut front and backside reflections, while others recommend backside-only AR to help maximize lens' durability.

Anti-fog properties—especially important with shields, side shields, goggles, and wrap-style frames that fit close to the face (more likely to “steam up”) and certain environments, like moving from heat to cold or vice versa—is another consideration when making photochromic, AR, or any lens recommendations to sporting patients or those working or playing in a glare-prone and rapidly or frequently changing environment.

In any case, photochromics with AR deliver a double dose of what eyes need most: comfort, convenience, and improved visual quality.

Photochromic and AR lenses have technical details that help ECPs sell. Images courtesy of Oakley (top) and Younger Optics (bottom)

OFF THE CHART

Glare is simply described as loss in visual performance or visibility because of excessive luminance, causing difficulty to differentiate various shades of gray.

Glare affects those with normal sight and healthy eyes and is particularly noticeable during nighttime driving. Any ocular abnormality increases intraocular light scatter and glare sensitivity. Ocular diseases that affect glare sensitivity include: corneal edema, irregularity, and opacification; cataract and post-cataract; vitreous syneresis; and macular edema.

Refractive surgery has also been identified as a possible cause of glare because of qualitative vision issues; even though patients may see 20/20 post-op, they may have problems with night vision, distortion, ghost images, and glare because of corneal haze and surface irregularities.

Other patients who can be light sensitive are those who are photophobic, either because of pathological causes (e.g., corneal abrasions) or other non-pathological causes.

Glare sensitivity tests measure the change in visual function resulting from a glare source. It can be tested using contrast detection tasks or by acuity-based measures.

Assessing contrast sensitivity helps provide information on how people view objects varying in size, contrast, and orientation. It can also help discover the possibility of underlying ocular disease and the need for additional testing.

Reading the Snellen chart to measure visual acuity has been the go-to to help determine 20/20 vision for many years. But we all know that vision as measured in a controlled exam room setting may not provide real-world results.

Each individual patient's activities at work and leisure, from day to night and coupled with the setting and environmental conditions, can all impact how well someone truly sees.

Essentially, measuring Snellen acuity indirectly assesses the spatial resolution capacity of the central retina: the higher spatial resolution, the better the vision. There are increasing clinical interest and use of contrast sensitivity and glare testing to help determine quality of vision in ocular and systemic diseases.

The Snellen chart assesses how the eyes see in black and white; contrast sensitivity testing measures how the eye sees in shades of gray and is determined using charts such as the Peli-Robson and Regan low-contrast acuity charts.

Contrast sensitivity can be enhanced with the right lenses. Image courtesy of Corning

To help patients both with normal and abnormal vision conditions, a variety of spectacle lens treatments can be utilized, including static tints.

However, because of ever-changing light conditions (too much, not enough, or different kinds), the environment-adapting, variable tint of photochromic lenses can help decrease incident light when levels are too high, yet allow light to reach the eye when levels are lower.

Changing light conditions require changing lenses. Image courtesy of Transitions Optical

The white paper, entitled “Contrast Sensitivity, Glare, and Quality of Vision” by Susan Stenson, MD, and Denis Fisk, finds that anti-reflective lenses help minimize reflections while maximizing transmitted light, which helps increase qualitative acuity while alleviating ocular discomfort.

The combination of photochromic lenses with AR helps achieve the proper balance between illumination and glare to maximize contrast sensitivity and offer visual comfort and convenience under varying light conditions. EB

MYTHBUSTING

Some myths, fables, even urban legends about photochromics and AR continue to survive and even thrive in the marketplace. Here are the myths, then the facts, so you can set your patients' (and even your colleagues') minds at ease. MYTH AR reduces the darkening ability of photochromic lenses. FACT It's been mathematically proven that this is not the case. The darkening, fade rate, and color of premium photochromic lenses with AR are all virtually the same as without AR; the differences in darkening performance are so small that instrumentation, not the human eye, would be needed to measure them. STUDY: According to a Transitions Optical study, an activated photochromic lens without AR front surface reflects four percent of incoming light, and 96 percent passes through the front surface. Photochromic molecules then filter out 83.6 percent of remaining light, and 15.7 percent of the original amount of light passes through the middle of the lens. The back surface of the lens reflects four percent of remaining light, so, in the end, 15.1 percent of the original amount of light reaches the eye. An activated photochromic lens with AR front surface reflects one percent of incoming light, and 99 percent passes through the front surface. Photochromic molecules then filter out 83.6 percent of remaining light, and 16.2 percent of the original amount of light passes through the middle of the lens. The back surface of the lens reflects one percent of remaining light, so that 16 percent of the original amount of light reaches the eye. CONCLUSION: The difference of .9 percent between light transmission without AR (15.1 percent) and with AR (16 percent) is negligible and the differences in darkening would not be apparent in a real-world setting. MYTH AR enhances photochromic technology. FACT Because AR maximizes the available light reaching the eyes, which indoors and in low light is a good thing, in bright sunlight AR can mean too much light may be reaching the eye, causing squinting and eye fatigue. Photochromic properties help reduce bright outdoor light, which complements AR by tamping down the amount of light reaching eyes and reducing visual discomfort. STUDY: Lenses with AR are clearer indoors than non-AR lenses. According to a photochromic technology leader, their photochromic lenses can reach 95 percent light transmission indoors, which makes the photochromic lenses with AR clearer than regular hard-coated clear lenses. CONCLUSION: According to Kenneth Scherick, OD, in “Enhancements to Quality of Vision with Photochromic Lenses and Antireflective Coating,” AR eliminates reflections on lens surfaces and maximizes transmitted light. However, too much light can result in eyestrain, squinting, or eye fatigue. Photochromic lenses reduce squinting and eyestrain by adapting to changing light, which makes them the ideal complement to AR treatments. MYTH AR increases the life of photochromic lenses. FACT Studies have found that photochromic lenses with AR are clearer in an un-activated state and may have an increase in lifetime performance. MYTH AR exacerbates the darker when cold, lighter when hot performance of photochromics. FACT It's a fact that photochromic treatment gets darker when it's cooler and lighter when it's warmer. For example, a major photochromic manufacturer's latest active product reaches 90 percent tint at 73 degrees F and 10 percent less tint at a warmer temperature: 80 percent at 95 degrees F. However, the company affirms that AR does not exacerbate the darker when colder, lighter when hotter performance of their photochromics. Clarifying the truths of AR/photochromic lenses helps ensure patient satisfaction. Image courtesy of Vision-Ease Lens