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ABCs of The Bs: Blue Light, Benefits of 20/20/20 Rule, Bicentric Grind

By Thomas Weissberger, RO

Abstract: With all of the focus on Blue Light and the use of digital devices, even to a higher extent during the COVID pandemic, a discussion is presented on the various aspects of the electromagnetic spectrum, including the differences between its visible and invisible bands. As well a brief synopsis is presented of the effects of Blue Light, both beneficial and toxic. The second portion of this paper covers some back to basics, specifically bicentric grind.

Size matters -The wavelengths in the electromagnetic spectrum At the end of this lesson the reader should be able to can be as short as a trillionth of a meter (smaller than an atom) for understand: gamma rays, to a meter for some radio waves, to as large as the entire a. The definition of the electromagnetic spectrum universe (an unfathomable number), and as math is infinite so too is b. Ionizing radiation the infinitely long potential of wavelengths we cannot even imagine. c. The visible light spectrum d. The effects of blue light –both positive and negative The spectrum is usually broken up into bands, divided into: radio e. Understand and define Digital Eye Strain waves, microwaves, infrared, visible light, , X-rays, and f. The 20/20/20/20 rule Gamma rays. The shorter the wavelength, the higher the energy g. Back to basics –bicentric grind created by these rays; the higher the energy, the more dangerous h. The effects of vertical imbalance they become. Wavelengths at the short-length range of the spectrum, from Gamma Rays to Ultraviolet are also known as Ionizing radiation, At the end of this lesson the reader should be able to use: consisting of subatomic particles or electromagnetic waves that have sufficient energy to ionize atoms or molecules by detaching electrons a. Total power formula to calculate power of cylinder in a from them1. Why this is both important and relevant to our topic is given axis b. Prentice’s rule to calculate prism and prism imbalance

Blue light Blue light is part of the visible portion of the electromagnetic spectrum. A reminder of the totality of the EM spectrum is that it encompasses everything from very dangerous radiation (including Gamma rays, that could turn you into the Hulk faster than a shortage of chocolate would) to the much longer wavelengths such as radio waves (which are only dangerous if you consider Rock and Roll music to be a danger to society).

57 that by effecting the molecules that make up our cells, they impact our cells by changing their structure (this is how UV gives us sunburn for example). Everyone today is aware of the negative effects of UV, because there is a physical reaction that can be felt and defined, but even in UV light, different wavelengths will have different ionizing properties, which is why UV is divided into three categories: UV A, UV B, and UV C; UV C having the shortest wavelengths, and thus the most damaging effects, as we have learned over the years.

Just next to UV rays we have Blue light, which shifts to the visible light spectrum (visible because the receptor cells in our eyes react to it), but still has a relatively short wavelength, and therefore emits a high energy level; thus, it is also called high energy visible light, or HEV.

Because blue light is such high energy, it also scatters very easily when reflecting off an object (think of how a shatters and is scattered everywhere when you drop it and it hits a ceramic floor for example. I know this to be true, because I dropped one of my wife’s favourite cups the other day, and not only did it shatter into thousands of pieces, but also caused my wife to emit an extremely high level of irate energy, which definitely effected my molecules); this has a couple of effects, one is that because it scatters everywhere, even when hitting air molecules, it makes the sky look blue; another is that it is harsh on our vision, as scattered unfocussed light enters our eye, reducing contrast sensitivity.

This issue has been identified since the late 1930’s, with the Ray Ban Shooter introduced in 1938 with the yellow “Kalichrome” . They were marketed as being able to increase clarity by sharpening detail and minimizing haze by blocking blue light2.

Does Blue light affect us and eye-health negatively? This is the million-dollar (or should I say multi-million-dollar) question, as the current market generates approximately $22 M USD3 in annual sales. The answers depend on whether they are provided by industry studies, or independent medical studies.

Blue light, especially in the 440 to 450 nm range has been shown to have adverse effects on pigs’ retinal cells. When these cells were irradiated with blue light in that wavelength range, cellular toxicity was noted, causing cell death2. This is part of the reasoning that companies have used to justify blue-blocking . On the other hand, there have been scientific studies that unequivocally state that no toxic or visual effects have been proven4. Note that most, if not all of the adverse effects of blue light are caused by the sun, not digital devices, and we all do want to ensure that we have proper protection from the sun. Blue light created by the sun is 50 times as strong as any man-made device or fixture.

Picture courtesy of all about Vision5

58 Digital Eye Strain (DES), due to man-made viewing devices can Because of these, recommendations from many medical institutions be attributed to the effects of blue light, but only in part! Other such as Harvard University6 include not using digital devices for components such as near fixation for prolonged periods of time, two to three hours before bed-time. lack of blinking, improper posture, and screen brightness and contrast issues can lead to DES, whose symptoms can include: When the light around you diminishes and changes to the red end of eyestrain, headaches, distorted or blurred vision, fluctuating vision, the spectrum (think of the beautiful colours of a sunset) it prompts dry eyes, overly watery eyes (interesting that opposites can both your body to release your body’s natural stores of melatonin, the be part of the same issue), Neck and shoulder pain, Lower back sleep-inducing hormone. pain, and Fatigue. We must address all of the components and have answers and solutions for each. But, should we block all blue light (because we can!)? Blocking all blue light has proven to be not a good idea (I know grammar, grammar, While writing this at my computer, I started to have “tired eyes” with but how else can I say it?); certain wavelengths of blue light (think discomfort, dryness, and difficulty maintaining focus, all because of the benefits of sunlight, in its full spectrum) have been shown to I neglected the 20/20/20 rule! “Physician, heal thyself” is a term we not only reduce depression associated with SAD (Seasonal Affective must all remember if we are to maintain our own eye comfort and Disorder), but also to improve cognitive and memory function (so you health. Remember, every 20 minutes look away into the distance won’t forget what I have written so quickly), and help you stay alert more than 20 feet for 20 seconds (this reminder brought to you at (so you won’t fall asleep while reading this I hope)7. no extra charge). After studying the info graphic above, I discovered there is a fourth “20” rule: Try to stay at least 20 inches (51 cm to So, does blue light effect vision and our eyes negatively? I cannot those metrically inclined) away from your screen. answer for you, it is up to each individual optician to follow their professional knowledge, education, and beliefs, and ensure that Back to our discussion, blue light at certain wavelengths can affect they are giving their clients advice based on that knowledge. If you our eyes, it can also affect our systems, as studies have shown prescribe what you believe in, then you are doing your professional that exposure to blue light can alter our circadian rhythm, our duty properly; and, based on the benefits of blue light in general, body’s natural sleep-wake cycle, as light sensed by our eyes (and it is worth considering blue-blocking coatings that are wavelength specific, not broad-band, so that the wearer gets the best protection while maintaining the beneficial effects.

If you are going to recommend to your wearer to protect their eyes with a blue filter, then you have to choose between a permanently tinted or coated lens, or a photochromic lens such as Transitions®, which has been clinically approved to block a percentage of blue light. Although the photochromic lens is the best solution, providing more comfort in differing light conditions, there is a marked resistance by younger age groups to wearing such. This is the hurdle that many lens manufacturers have been trying to overcome with widespread marketing initiatives. As well, many filters do have even our skin has some blue light a yellowish component, -although that has been reduced with new sensors (who knew?)) that can technologies and processes, which will increase resistance to their perceive the difference between use by many wearers. These are the circumstances where we must bright daylight (with its intense guide the wearer to the best solution for their needs, and for that blue light waves) and the warmer, to happen, we must fully understand the issues, and the solutions! redder tones that signal the day is ending. If we are exposed to Bicentric Grind, a Back-to-Basics Topic blue light late in the day, then we How many of you out there have used bicentric grind on lenses to might end up like this: solve issues? First of all, what are the issues to solve?

Besides looking like a zombie What is bicentric grind? Bicentric means literally two centers, and the next morning, lack of sleep as the term implies the lens will be ground with two centers angled or disruptions in our sleep cycle to each other. It is also known as slab-off, as a “slab” of the lens is can have many negative effects ground away. There are also ways of creating slab-on, used on the on our health5, such as elevated opposite lens. Slab-off gives base up prism, so it is always used on risks of hormone-related cancers like breast and prostate cancer; the higher minus or lower plus. It is usually ground to the nearest obesity, as it can lower levels of leptin (a chemical that signals quarter of a diopter, but always less than the actual amount of prism fullness after meals), thus making one eat more; and metabolic created (see example below). changes, especially in blood sugar, with potential risk increases of Diabetes.

59 Traditionally, bicentric was used in bifocals because the wearer was forced to look below the distance optical center to read (around 8 mm for a flat top bifocal, segment being 3 mm below D.O.C. and then seg center 5 mm below that). The example of the stairs issue is clearly based on single vision, as looking at stairs through reading add will mean they are out of focus anyway. In order to determine the amount of vertical prism in an S.V. lens when looking down, we must determine how far below center the wearer is looking. To do that, we need to observe both the fit of the and the angle of posture and gaze (the practical aspects of optics). One of the ways to do that is to have the patient wear the frames and look down at the floor while standing and try to mark the point through which they are looking to give a distance away from center. We ABC then need to find the dioptric power in the vertical meridian. You can use the cylinder power formula: F = F + F (Sin2 ), F = A is lens blank with a dummy lens cemented (temporarily to front) to Tot Sph cyl θ sph give enough thickness to grind the with prism without touching top power of the sphere; Fcyl = power of the cylinder; and θ = number portion; B is showing lens ground with prism in the bottom half (slab on of degrees away from written axis. So, for example if your written front for glass lens, process would be done on back for organic lens; C axis was 030, as in RX: OD –2.00 -1.50 x 030 then the vertical, 090 is final product with prism on bottom half of lens only. Note: slab-off line is at OC for SV lens, or at the segment top for bifocal. axis would be 60° away.

2 Using our formula => FTot = FSph + Fcyl(Sin θ) => FTot = -2.00 + Bicentric grind is used to negate the effects of vertical imbalance. (-1.50)(Sin2060) =>

As we know, when we look away from the optical center of a lens FTot = -2.00 + (-1.50)*0.75 = -2.00 + (-1.125) = -3.125 D we look through prism. The amount of prismatic effect is based The OS RX is –1.00 on the dioptric strength of the lens in the 090° meridian; what this means is that if we look above or below the optical center of Thus vertical prism at 8 mm below center would be OD = -3.25 a lens we are looking through vertical prism. Looking through *0.8 = 2.6 BD, OS = -1.00 * 0.8 = 0.8 BD, using Prentice’s Rule prism in and of itself is not necessarily an (major) issue, but if prism formula covered in lesson one. The vertical imbalance would the prism amount is different for each eye, then the further from be 2.6 - 0.8 = 1.8 VI. We do not give a prism base direction to the center we look, the more Vertical Imbalance is created. As discussed VI. Slab-off would be used on OD => 1.50 or 1.75 BU. in an earlier lesson, when the prismatic imbalance vertically is Related terms: slab-on greater than 0.25 D the brain starts to lose the ability to fuse the images from both eyes, and the wearer starts to experience diplopia References: (literally double vision). Causes for differences in the 90° meridian 1. Ionizing radiation – Wikipedia include Aniseikonia (a difference of more than 1.50 D correction 2. ray-ban_history_en.pdf (luxottica.com) 3. www.marketwatch.com/press-release/blue-light-blocking-glasses-market-size- between the two eyes; and antimetropia, where one eye needs a will-grow-at-cagr-of-80-during-2021-2026-with-top-countries-data-2021-05-23 plus correction, and the other a minus. 4. The effect of blue-light blocking spectacle lenses on visual performance, macular health and the sleep-wake cycle: a systematic review of the literature - Diplopia at best is uncomfortable and at worse dangerous. Lawrenson - 2017 - Ophthalmic and Physiological Optics - Wiley Online Library –Lawson OD, et al. Uncomfortable because the brain cannot handle trying to process 5. Infographic: 7 Things You're Doing at Your Desk That Will Give You Eye Strain - two images at the same time; dangerous because it reduces the AllAboutVision.com ability of orienting oneself in their environment, which can be a real 6. www.health.harvard.edu/staying-healthy/blue-light-has-a-dark-side 7. www.healthline.com/health/what-is-blue-light#risks-and-side-effects - Medically injury risk, especially on stairs (imagine seeing two different stairs reviewed by Jenna Stoddard, OD — Written by Rebecca Joy Stanborough, MFA at two different heights and not knowing on which one to step). on April 16, 2021

I am a second generation optician and have made all aspects of opticianry and optics my life. I have over 10 years of teaching experience as a former professor in the Dispensing Opticians’ program at Seneca College and at Georgian College. I was also responsible for The Practical modernization of the optical curriculum. Professor I am a trainer and trainee (One never stops learning!), and I am available to share my knowledge and experience Optical Solutions with today’s eye care professionals. As the owner for the Real World of Special Eyes Optical Services, I am dedicated to supporting the optical industry. You can reach out to me at [email protected].

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