LET'S BE CLEAR ABOUT BLUE
By Deborah Kotob, ABOM
Upon completion of this course participants will be able to:
- Define actinic rays
- Explain the sources of UVR and HEV
- Describe the two types of blue light and their effects on vision, ocular tissue, and our chronological circadian clock
- Explain why letting beneficial blue light through a lens is as important as cutting the transmission of UVR and HEV blue light
- List why we should have UVR and HEV blue light filters in our everyday clear lenses.
- Describe how lenses made with UV+420™ technology filter high energy visible (HEV) blue light but transmit beneficial blue wavelengths tuned to our circadian rhythm
Deborah Kotob, ABOM, is the Director of Education and Training for Jobson Medical Information. Her experience spans more than twenty years in the optical industry. During this time, her roles included optical boutiques owner, optician, optical frame sales, and over ten years in lens manufacturing as a Lens Consultant, Trainer, and LMS content developer. She lectures, trains, conducts webinars on a variety of optical and practice development topics.
This course is approved for one (1) hour of CE credit by the American Board of Opticianry (ABO) for Technical Ophthalmic Level 2. Course # STWJHI035-02
This is a product spotlight CE supported by an educational grant from Mitsui Chemicals.
This course aims to expand the conversation within the optical industry about sunlight’s potential to harm the eye. While most of us know that ultraviolet radiation damages the skin, fewer realize it can hurt the eyes, and even fewer are aware of high energy visible (HEV) blue lights’ phototoxic effects on our eyes. This article intends to increase awareness that UVR and HEV light are actinic and can produce photochemical damage to the skin and ocular tissues with prolonged or intense exposure, such as sunlight. We will review the cumulative and irreversible nature of actinic light injury from UVR and HEV blue, and how our clear glasses should have protection built in for all those times we are outdoors without sunglasses. And finally, we will be clear about what is known and under investigation relative to the ocular and circadian rhythm effects of blue light from prolonged exposure to LED and LCD indoor lighting and digital screens.
UVR and HEV blue light, what are they?
UVR and HEV blue light are actinic high energy electromagnetic wavelengths with the potential to harm biological tissue of the skin and the eyes. The damage that occurs is cumulative and irreversible, accruing over one’s lifetime. Preventative measures become the first line of defense since photo-oxidative injury over a lifetime is a potential causal factor in incurable and blinding disorders later in life, such as age-related macular degeneration. It is imperative that we reduce our lifetime exposure to these rays; to do so, we must start young. A child’s eye transmits up to 70 percent more UVR to its young retinae than an adult eye. Consider that a child’s retina has a window of exposure in the 320 nm UV range, and their crystalline lens is not yet pigmented with yellow chromophores of an adult eye, which absorb and reduce the transmission of blue wavelengths to the retina. UVR and HEV harmful effects are intensified with increased photosensitivity which results from ingesting certain common medications or herbal supplements. Something as simple as aspirin increases photosensitivity of the skin and eyes. The aged eye accumulates lipofuscin, byproducts of the visual cycle and potent photosensitizers.
BE CLEAR ABOUT UVR FACTS
Ultraviolet light (UV) is non-ionizing radiation that can damage DNA (Fig. 2); the accumulation of DNA damage kills cells. UV radiation contributes nothing to sight but can cause irreversible damage to ocular tissue, including retinal cells. Over time, cataracts and other eye maladies develop from UV damage.
- The ozone absorbs UVC rays (100 to 280 nm).
- UVB rays (280 to 315 nm) are absorbed mainly by the cornea, with the crystalline lens absorbing most of the remainder
- The crystalline lens absorbs UVA rays (315 to 380 nm).
Important note: Young eyes of those under age 20 are more susceptible to UV damage to their retina
UVR exposure increases at higher altitudes and closer to the equator. Primary source: sunlight (artificial sources exist, such as from a welder’s arc or UV sterilization or curing lamps)
BE CLEAR ABOUT BLUE LIGHT FACTS
There are two types of blue light, HEV and beneficial.
Some international organizations, such as ISO6, list the reference range for visible light starting at 380 nm, while others say that 380 nm and 400 nm are UVR. Regardless, this range of high-energy light waves can be phototoxic to skin and ocular tissue. We will use the HEV blue light reference range of approximately 400 to 455 nm. HEV is adjacent to ultraviolet radiation, with energy levels just below UVA. HEV blue light is comprised of visible blue-violet wavelengths which transmit through the lens to the retina. Light in the 400 to 420 nm part of the spectrum is thought to be particularly harmful. In standardized lab experiments using cell cultures, Professor Richard Funk of the Technical University of Dresden showed retinal neuronal cells experience greater oxidative stress when exposed to 411 nm light versus 470 nm light, and the shorter, higher energy blue wavelengths show indications of cell death (apoptosis).1 Shorter wavelength blue light contains higher energ y, meaning that a lower radiant dose is needed to reach the threshold for damage. Also, intensity increases with proximity. Damage to ocular cells of our eye, including retinal cells, is dose and wavelength-dependent. Photochemical damage only occurs in cells that absorb specific wavelengths of light. For cell damage from high-energy light to occur, the cell must contain chromophores that absorb high-energy wavelengths. In a series of animal studies, even retinal damage was wavelength dependent. For example, the photoreceptor cells were most sensitive to damage from invisible UV and the shortest visible blue from 400 nm to 440 nm.
In comparison, the retinal pigment epithelial (RPE) cells were most sensitive to damage from 440 nm up to approximately 467 nm.2 Age also plays a role in actinic light transmission to the retina. Because young crystalline lenses are more transparent, and people under 20 tend to participate in more outdoor activities, their retinas are more likely to be exposed to and absorb this harmful light. “Blue-violet light increases oxidative stress in our aging model of the outer retina while simultaneously decreasing natural antioxidant defenses,” (Marie, M. et al. (2018). “Light action spectrum on oxidative stress and mitochondrial damage in A2E-loaded retinal pigment epithelium cells,” (Cell Death and Disease).3
The primary source of HEV blue light is sunlight. (Artificial LED and LCD lighting and digital device screens have increased our exposure to blue rays. But there is currently no conclusive evidence that the intensities and wavelengths emitted by these lights and digital screens are causing photochemical damage to our eyes.)
Why we do not want to block beneficial blue light (460 to 490 nm): Our circadian rhythm is entrained to these wavelengths of light, and when exposed to them in the morning, upon waking, they set our biological clock 24-hour sleep/wake cycle. Exposure to these wavelengths causes the hormone serotonin to rise along with other brain chemicals that cause us to feel awake, happy and alert. In the normal cycle of light and darkness, these chemical levels drop as the sunsets and the levels of our sleep hormone, melatonin, rise. Unfortunately, artificial lighting and bright blue-rich digital screens expose our eyes to light levels that can interfere with our normal sleep cycle. According to Bailes, H.J., and Lucas, R.J. (2013), human melanopsin forms a pigment maximally sensitive to blue light (lmax 479 nm), supporting activation of Gq/11 and Gi/o signaling cascades, (Proc. Biol. Sci. 280, 20122987).4 It is recommended that these wavelengths be avoided within two to three hours before bedtime to avoid sleep disruption.
BENEFICIAL BLUE LIGHT AND NORMAL EYE DEVELOPMENT
Beneficial blue wavelengths of light are tuned to our intrinsically photoreceptive retinal ganglion cells (ipRGCs), which “convey irradiance information centrally via the optic nerve to influence several functions including photoentrainment of the biological clock located in the hypothalamus, the pupillary light reflex, sleep and perhaps some aspects of vision,” (pubmed.ncbi.nlm.nih.gov/22160822). When these cells are exposed to beneficial blue wavelengths, they set our master clock rhythms to the light/dark cycle but also modulate refractive development.
“Increasing evidence implicates diurnal and circadian rhythms in eye growth and refractive error development. In both humans and animals, ocular length and other anatomical and physiological features of the eye undergo diurnal oscillations. Retinal signaling is now believed to influence refractive development; dopamine, an important neurotransmitter found in the retina, not only entrains intrinsic retinal rhythms to the light/dark cycle but also modulates refractive development. How, or if, modern light exposures and circadian dysregulation contribute to refractive development are not known,” (Graef K and Schaeffel, F. Control of accommodation by longitudinal chromatic aberration and blue cones. J of Vis. 2012;12(1):14).5
Normal sleep/wake cycles are critical to our physical and mental health and even normal eye development in children. Therefore, we do not want to block them during the day when they increase dopamine and happy brain chemicals like serotonin to keep us awake, alert and happy. However, if the eyes are exposed to these wavelengths too close to bedtime (within two to three hours), melatonin, our sleep hormone, will be suppressed, disrupting normal sleep patterns and leading to sleep deprivation. If one cannot make themselves put down their digital devices at night, then at a minimum, change the settings to dark mode or use the manufacturer’s settings to reduce blue light emissions.
ARTIFICIAL AND SOLAR: TWO SOURCES OF BLUE LIGHT
Blue light effects differ for indoor exposure from LED/LCD screens and lighting versus sunlight. Actinic light (UVR and HEV) exposure from sunlight can damage ocular structures from the cornea to the lens and the retina. While sunlight exposure can be phototoxic to ocular tissue and the delicate tissues around the eyes and lids, it can also contribute to disabling and discomfort glare.
Indoor exposure to HEV blue may be one of the contributing factors to digital eye fatigue and discomfort experienced with extended screen time. The proximity of screens, especially smartphones positioned closer to our eyes, increases intensity, so closer equals higher intensity which equates to more visual discomfort. According to Prevent Blindness America, “Blue light from computer screens and digital devices can decrease contrast, contributing to digital eyestrain and computer vision syndrome symptoms. Symptoms of eyestrain include sore or irritated eyes and difficulty focusing.” Our exposure to indoor blue light has increased due to the rise in LED and LCD lighting, and digital screen exposure. The long-term effects of this lowlevel intensity and prolonged daily exposure are still under study, and it will take time for the long-term cumulative effects to manifest. But to date, no study has conclusively shown a link between digital screen emissions and biological damage to ocular structures. A quick sidebar on UVR is our common belief that we are protected from UVR indoors by UV filters in window glass. But windowpanes can reportedly transmit as high as 25 percent UVR, highlighting the added benefit of wearing lenses indoors that block UVR. And as noted earlier in this article, there are artificial sources of UVR, such as ARC lamps used in welding , CFL lamps, tanning beds and UVR sterilizers (used for everything from food sterilization to curing artificial acrylic and gel nail extensions).
UV+420CUT™ TECHNOLOGY BY MITSUI CHEMICALS
UV+420cut™ technology makes it possible to produce clear lenses that block high energy light from the UV spectrum up to 420 nm visible light. Most lenses that block HEV light are made with a special coating on the lens surface that reflects blue wavelengths. In lenses made with UV+420cut™ technology, the specially treated dye is dispersed in the lens material itself. This “in-mass” technology blocks light by absorbing it. As a result, such lenses have good UV-blocking performance, last longer (because scratches to the surface do not degrade their function) and do not give off a bluish reflection.
Mitsui Chemicals’ UV+420cut™ technology is a clear in-mass lens technology that cuts HEV blue light in the 400 to 420 nm spectrum and blocks UV radiation. The technology is, in essence, a high-pass optical filter that filters by wavelength, passing only longer wavelengths (lower frequencies). UV+420cut™ Technology enhances the protection achieved in our clear everyday lenses against the types of light that can damage the eyes. And lenses with UV420+cut™ technology protect us from actinic light without altering the colors we see and without the cosmetic disadvantage of yellow lenses or blue-violet AR reflex colors. Not all blue filter or blocking lenses are created equal, making it essential that you see their transmission chart. Depending on the manufacturer, the transmission curves of both UV and short wavelength blue light will differ.
Colors look natural, and lenses look clear: The 400 to 420 nm light filtered out by UV+420cut™ technology does not affect how colors appear. When an object absorbs a color, the human eye sees the opposing (complementary) color, which is why things appear yellow when blue light is blocked. This explains why most in-mass type lenses designed to block HEV light have a yellowish tint.
By controlling the dye dispersed in the lens material, UV+420cut™ in-mass technology blocks high-energy light without interfering with normal color perception while looking nice and clear.
MR™ LENS MATERIALS WITH UV+420CUT™ TECHNOLOGY
Lenses with UV+420cut™ technology are made with the same high refractive index materials used for the MR™ series. The MR™ series utilizes a unique monomer polymerization process to create optical materials with a high refractive index and Abbe value, low specific gravity (weight) and high impact resistance. A high refractive index means that lenses can be made lighter and thinner. Moreover, the material has the strength required for ophthalmic lenses and good fabrication properties, which is ideal for rimless frames and making high-curve lenses. In addition, MR™ high index material produces better optics due to the lower lens aberrations associated with its high Abbe value. Although this course is about UV+420cut™ technology used to make clear corrective eyewear, the technolog y can be used to manufacture fashion and sun lenses.
In summary, this course emphasized the importance of reducing our lifetime exposure to actinic light (UVR and HEV blue) as a reasonable precaution against ocular injury and damage from the phototoxicity of high-energ y wavelengths. We have also learned about protective lenses that can help us accomplish the goal of reducing our lifetime exposure to actinic UVR and HEV light. Mitsui Chemicals’ UV+420cut™ is a clear lens technolog y that cuts HEV blue light in the 400 to 420 nm spectrum, in addition to blocking of UV radiation, thereby enhancing the level of protection in our clear everyday lenses against the types of light that can damage the eyes. Earn your patients’ trust by helping them prevent damage to their eyes to preserve their eye health.