L&T: RxPertise


The Lowdown on Blue Light

By Palmer R. Cook, OD

Remember K-Mart’s Bluelight Specials? They were part of K-mart shoppers’ culture from 1965 until 1991. They were even revived during the recent holiday season. Back in the day, K-mart’s Bluelight Specials were state-of the-art-marketing. Shoppers heard the Bluelight Special announcements and streamed to the department with the blue flashing light for the hot 20-minute specials.

Today our industry’s marketing powerhouses are offering a different kind of blue light announcements that eyecare providers are finding hard to ignore. And the issues of blue light are not limited to the ophthalmic industry. Architects, lighting specialists and the entire electronics industry seem to be searching for answers and direction.

Most eyecare providers want good patient- perceptible outcomes, or at least they want assurance that their products and care regimens are proven and scientifically sound. The retinal receptors are biological transducers. Any engineer will tell you that a transducer is something that changes one form of energy into another. Optically speaking, materials that fluoresce under UV stimulation, such as the sodium fluorescein we use in fitting GP contacts, are a form of transducer. This is because they convert invisible UV light into visible light.

The rods and cones are transducers in that they convert light energy (photons) into electrical energy. Inside these retinal receptors are stacks of membrane-discs. When photons enter the end of retinal receptors, they trigger a chemical reaction by impacting stacks of membrane-discs, creating electrical energy. This energy is then transmitted via nerve pathways to the brain. This electrical energy carries information to our visual cortex and other cognitive parts of our brain to create our most critical sense, visual perception. The membrane-discs in the receptors regenerate quickly to be ready for the incoming photons, and in a perfect world this reaction/regeneration cycle would continue forever without fail.

Retinal ganglion cells have long been thought to be collector cells for impulses from rods and cones that pass through bipolar and amacrine cells to the ganglion cells, which have axons that penetrate the brain. There is now research indicating that these retinal ganglion cells may have a light receptor function related to pupillary changes and the circadian rhythm.

Light comes in various wavelengths given in colors or numbers (e.g., nanometers or nm). Red light is in the 622 to 780 nm range, yellow-green light is in the 570 to 510 nm range, and blue-violet light falls in the 445 to 400 nm range. Light, just like champion boxers, packs a punch with red being a lightweight, yellow-green being a middleweight and blue-violet packing the heavyweight’s punch. Blue-violet, having the most energy of the visible wavelengths is called HEV (high-energy visible) light. HEV light is suspected to have enough energy that it may be causing permanent damage to the retinal receptors (and visual acuity) over long-term exposure. A more immediate effect may occur, disrupting our sleep patterns and pupillary actions as the result of HEV affecting the retinal ganglion cells.

The lyrics of the old song, “I got plenty of nothing. And nothing is plenty for me,” just don’t apply to HEV light. HEV wavelengths have a lot of energy and seem to be multifunctional, affecting more than just the retinal image. They affect our circadian rhythms including our sleep patterns, and they also play a role in our pupillary function. Some manufacturers apparently believe that a 20 to 30 percent reduction in HEV exposure preserves the needed roles played by those wavelengths. They also believe that this level of blockage may be effective in preventing long-term retinal damage. Unbiased research in the future may prove them to be correct. In the meantime, we must exercise our best judgment to protect our patients.

Centuries ago people had a wide variety of diseases, many of which we now can easily cure, but there is one disease they didn’t experience; yet it runs rampant through our population today. In a time when life expectancy was 25 to 35 years, nearly everyone died before they were 40, which eliminated presbyopia as a problem. Presbyopia is a disease of longevity, and everyone who lives long enough experiences it. In fact, presbyopia is so common that we simply accept it and deal with it, although we have all experienced the “presbyope-in-denial.”

Is it possible that age-related macular degeneration (ARMD) is analogous to presbyopia? Could the endless hammering of the photons of HEV light on the membrane-discs of the retinal receptors be causing the damage we know of as ARMD?

As longevity increases, and as the average age of the population rises, macular degeneration will be an ever-growing problem. Today this problem is being addressed nutritionally with various compounds containing lutein and zeaxanthin. Visual aids are also employed to make best use of less unaffected retinal areas.

In the past few decades, we have had huge cultural changes. Cell phones seem to be in constant use, and their tiny screens cause users to use relative distance magnification (i.e., they are held at a close viewing distance). People gaze steadily for hours at computer screens and commonly experience a reduced blink rate and dry eye syndrome, not to mention the adaptation changes that occur as they repeatedly switch from paperwork (at one luminance level) to their screens (at a different level). This is in addition to the HEV exposure they are receiving from those screens.

“First Do No Harm” is a part of the Hippocratic approach to medicine, and it is a good mindset for all health care professionals. In the days before organic lenses, it was found that certain tints, when exposed to sunlight, emitted small amounts of radiation. These tints quickly fell into disfavor, and no such problem exists today. Among the various ways of reducing HEV exposure, the most serious negative aspects seem to be limited to cost, practicality, appearance and potential for creating hazards for certain tasks such as night driving. The issue of whether increased cost will create a hardship is a matter for discussion between the provider and the consumer, but all ECPs should be prepared to discuss the value in clear and reasonable terms.

I spend a lot of time on a MacBook Pro with a 15-inch screen set to a fairly high brightness level. One evening, while reading a discussion related to HEV exposure, I decided to measure the light output of my computer’s screen at its current setting, which seemed comfortable enough. Then I reduced the brightness tenfold, which reduced my HEV exposure from the screen by 90 percent. I found that setting to be quite comfortable, as was a reduction by 20 to 30 percent. If the concern is one of exposure to computer and phone screens, would it be practical to simply recommend that the screen brightness be reduced, and would patients comply?

Screen filters are available for phones and computers, and they are relatively inexpensive. Perhaps we should caution our patients that if the screen brightness is increased when the filter is used, the overall reduction of HEV exposure can be lost.

For iPhones and iPads, there is an app (Night Shift, if you are running iOS9.3) that reduces the blue output of your screen. It can be set like an alarm clock for the hours you want it to run. Flux is a free app for Windows, Mac and Linux that appears to be a mild red-orange filter. It turns on at sunset and off at sunrise. Another app, Twilight, for Android devices works similarly. The reducing of HEV prior to sleep addresses the problem of disrupting the circadian rhythm, but to move toward pre-cell phone and pre-computer levels of HEV exposure, these apps should probably be used 24/7.

Appearance is a highly subjective matter. The blue-violet reflection from an HEV-reducing-coating, might be acceptable to some and garish to others. The same can be said for lenses that use absorptive tints to reduce HEV exposure. These problems can be addressed by having samples of the coatings and tints available in your dispensary.

Even a 5 percent lens tint will have the effect of reducing the reach of headlights by that same percentage. At 60 miles an hour you are traveling at 88 feet per second. If your reaction time is 1.5 seconds, and if you can get your foot on the brake pedal in 0.3 seconds, you will have traveled a little over 158 feet before you can begin to slow down. With full braking at 60 mph, your stopping distance might be 180 feet. This total stopping distance of 338 feet means that if the reach of your headlights was less than the length of a football field, and you are traveling at 60 mph, you will not see the Bridge Is Out sawhorse in time to avoid hitting it.

Patients wearing HEV-reducing lenses may have those “blue light auto headlamp,” which may use increased blue light at the expense of filters that reduce the longer wavelengths to meet the light output requirements. Also, the plastic lensed headlamps of older cars may already be limiting the reach of your patients’ headlights. On the plus side, HEV light tends to be scattered more readily by the eye, so limiting it may have some beneficial effect—solid research is needed.

Some of the nutritional approaches to macular problems may be more preventative than therapeutic, and there are claims of nutritional treatments that reverse the effects of macular degeneration. Limiting HEV exposure has been hotly debated as a way of protecting the retinal receptors. One approach is to absorb HEV selectively by using a lens tint such as BPI’s #37855 at 15 percent overall absorption to get approximately a 30 percent reduction from about 430 nanometers to about 530 nanometers.

The immediate benefit for late-night computer users could be to relieve them from the insomnia and next-day-fatigue that is said to arise from excessive HEV exposure from their screens. This tint is also an effective UV blocker with virtually 100 percent blockage from 400 nm and lower, so UV blockers are not needed if standard plastic lenses are used.

Another way to partially eliminate HEV is to use a coating. These coatings are similar to an anti-reflective lens treatment, but they are adjusted to partially eliminate HEV. These coatings have a distinct blue appearance. Some manufacturers refuse to give HEV transmittance values for these coatings. They say their products “filter,” yet they supply only the value of the reflected blue light, which may be misleading because of the wave summation caused by the coating.

There are a variety of coatings that use this wave interference approach to limit HEV exposure. Nikon offers SeeCoat Blue, Essilor’s entry is Prevencia, iBlu Coat is from PFO Global, and Hoya provides Recharge with a claim of a 30 percent HEV reduction, to name but a few.

When coating technology is used to limit HEV transmission, the lenses can be held an inch or so over a white paper to reveal a somewhat yellowish cast. This yellowish cast indicates that some blue-violet light is selectively eliminated. This effect is not easy to discern when viewing through these coatings.

Tinting a lens to eliminate part of the HEV light causes it to become pale yellow in appearance, and this may give a sallow appearance to the sclera and ocular adnexa. Light transmitted by these lenses will also have a yellowish cast when it falls on white paper.

In the long haul, damage from HEV light and perhaps even longer wavelengths may be proven to have cumulative effect resulting in macular degeneration. When, and if, our life expectancies reach 125 years or so, the question of HEV’s relationship to macular damage may be viewed in quite a different way than we now consider it. At some point presbyopia must have been considered a disease of aging instead of an unavoidable Rite of Passage into our middle years.

If our life expectancies reach 125 or more years, we may view all visible light as potentially hazardous. Hospital nurseries of the future may fit all newborns with absorptive lenses. If the retinal receptors are sensitive to HEV damage, is it possible that we may eventually learn that longer wavelengths are also toxic to the receptors? We may ultimately discover that even the orange and red wavelengths take their toll over a very long time. This paints a rather Orwellian future in which there may be great arguments about requiring citizens to wear darkly tinted lenses at all times.

The questions concerning HEV light will persist until more definitive research is available. Sleep patterns and pupillary functions aside, although they are important too, the elephant in the corner of the room is the burgeoning problem of macular degeneration. It is a frustrating disease that robs too many of their most important sense, vision, at a time in life that should be theirs to enjoy.

Optometrists and ophthalmologists are formally educated in science and optics, but without more data, judging what is best for your trusting patients is difficult indeed. Contact your preferred lab’s consultation service for data on the transmission curves and availability of lens products that reduce UV and HEV, and for unbiased studies (rather than sponsored “white papers”) that could be subject to bias about the benefits of those products. If your lab has no supporting evidence, they will pass your request to the appropriate manufacturers. ■

Contributing editor Palmer R. Cook, OD, is an optometric educator and optical dispensing expert.