LEARNING OBJECTIVES
- Understand UV, it’s proven biological effects and the known threats to eye health,
- Be aware of prevailing misconceptions about still to be determined blue light effects from screen use,
- Realise the UV protection gap in four out of five lenses, and
- Be aware of the solution available to prevent UV radiation damage.
UV and Blue Light Protection: Common Misconceptions
Counter to what many eye care professionals (ECPS) believe, UV is not a problem that has already been solved!
Many ECPs have firm but misguided beliefs about the level of UV protection that existing lenses provide. We mistakenly believe that clear lenses, like polycarbonate, already have full UV400 protection built in.
Figure 1. Just as the UV damage to this young woman’s skin is invisible to the naked eye and only revealed when a UV camera exposes the hidden harm, so is retinal damage hidden and painless until advanced enough to cause vision loss.
Why are we talking about prioritising light protection for the eyes? In eye care, the conversation surrounding light protection for the eyes has become hyper-focused. Alarmingly, the focus is not on the proven high-level threat to the eye from the harmful effects of UV radiation (UVR) exposure.1 Instead, our focus increasingly centres on the purported blue light hazards from digital device screen emissions. The harmful eye health effects of UV radiation exposure are obscured by the media buzz surrounding blue light risk from digital devices, the long-term harmful effects of which remain highly inconclusive.
Compounding the confusion around light protection is the fact that industry veterans and new ECPs alike, have been caught up in the momentum around blue light, where scientific findings are still in flux. For example, ECPs are often under the mistaken belief that a blue filter anti reflective coating, or a lens filter, blocks a high percentage of blue light. In fact the reduction, and therefore the protection, is quite minimal. It is difficult for the ECP to sort through the inconsistent and often conflicting information and claims to make informed decisions. For example, which wavebands of blue light are considered harmful long term, versus those that may contribute to digital eye fatigue?
Dispelling firmly held misconceptions is challenging. This course will give the facts and supporting science-based data from which we can reframe our understanding of UV protection in lenses, the blue light hazard from screen use, and the undisputed dangers posed by UV radiation exposure to the eyes, particularly young ones.
In this course, you’ll be given information to help you understand the need to extend UV protection to UV 400nm in lenses, beyond the current 380nm for ‘100% UV protection’. This course will also address the vital need to refocus the light protection conversation on the dangers posed by UV radiation to the eye and surrounding skin tissues. It will provide a perspective on the blue light hazard, and the lenses and coatings purported to attenuate them. Finally, it will discuss a clear lens solution that provides increased UV protection.
What is UVR?
Ultraviolet radiation is light energy that ranges from 100 to 400nm on the electromagnetic (EM) spectrum.
Violet is the highest energy visible light that borders UVA on the electro- magnetic spectrum. ‘Ultraviolet’ means beyond violet (beyond visible violet light), in other words, the rays are invisible.
Shorter wavelengths produce EM waves of a higher frequency and therefore higher energy. Blue visible light has a longer wavelength and therefore contains less energy than UVA. UVA contains less energy than UVB. UVR is actinic light, meaning that it has energy levels high enough to produce photochemical damage to biological structures when absorbed. Only two parts of our bodies absorb and are susceptible to damage by light; the skin and the eyes. Different layers of skin and eyes absorb specific ranges or bands of wavelengths. Higher energy waves are primarily absorbed by the outer layers of the skin and eyes, while longer, less energetic waves penetrate deeper into tissues of the skin and eyes. The ability of actinic UV light to harm the eyes or skin is wavelength dependent.
“The primate/human eye has unique filtering characteristics that determine in which area of the eye each wavelength of light will be absorbed. Both UVA and UVB induce cataract formation. The removal of these wavelengths from ocular exposure will greatly reduce the risk of early cataract formation,” states Joan E. Roberts, PhD, in Photobiology of the Lens.2
UVR Effects on Eye Health
UVR is an undisputed threat to eye health. Scientific and international regulatory bodies agree: UV is harmful to the human eye and its surrounding tissues.3 UVR is EM radiation that can cause ocular oxidative photo-degradation that can result in severe damage to the eyes and their surrounding structures. While UV contributes little to nothing to sight, it can severely damage the eyes and their surrounding structures.
UV interacts strongly with molecules in human cells. Research has shown that the effects of UV damage accumulate over a lifetime; and that early and frequent retinal exposure may contribute to age-related macular degeneration later on in life.3 Other known effects of UV exposure include:
- Photo-aging of the eyelids and surrounding skin,
- Skin cancers of the same regions, accounting for up to 10% of all skin cancers,
- Degenerative and unsightly growths on the conjunctiva,
- Acute and painful inflammation of the cornea,
- Melanoma of the iris – a potentially deadly type of cancer, and
- Nuclear sclerosis of the lens, leading to reduced vision and ultimately to cataracts that require surgery.
Damage and Disease Caused by UVR
The damage caused by UVR can be acute or chronic. Acute damage occurs with short but intense exposure. Most acute damage is painful, temporary and will heal. Chronic damage and subsequent disease development are caused by much lower levels of exposure over a long period, often many years. Chronic damage is phototoxic and photo-aging. It accumulates over a lifetime, and there is no cure – the damage is irreversible. Chronic conditions are insidious, and because they happen gradually, they go undetected until significant irreparable damage is present.
Conditions caused by UVR include:
Eyelids and periorbital skin
UVR damage to the eyelids is common. Sunscreen should be applied to the eyelids to prevent injury, but research indicates that people are non-compliant because of eye irritation.
Skin
UVR exposure results in photo-aging of the eyelids and surrounding skin. UV photo damage thickens the skin, resulting in deep premature wrinkles. UVR damage to sebaceous glands can lead to xerosis (dry skin). Actinic keratosis is an advanced type of damage to the skin, characterised by dry red patches. It is considered pre-cancerous. Eyelid cancers represent 5 to 10% of all skin cancers and can easily metastasise or spread.4
Cornea
Ultraviolet keratitis, also known as photokeratitis, is a painful eye condition caused by exposure to ultraviolet rays. It can be referred to as sunburn of the cornea.
Conjunctiva
A pinguecula is a thickened deposit of fat, protein and calcium that is visible over the white of the eye. Unless it grows into a pterygium, it is usually only an unsightly cosmetic problem.
Iris
Melanoma tumors are the most common cancer of the eye, and evidence suggests that UVR is one of its leading causes. When located on the iris, the most common location is at the bottom, where daylight UVR exposure is strongest.
Lens
UVR causes pre-cataractous changes by causing proteins to clump together. As the eye ages, protective pigments in the lens convert to pigments that react to UVR, further damaging the outer layer of the lens and lens proteins. When enough damage has accumulated, cataracts develop. Both UVA and UVB induce cataract formation. In Biology of the Human Lens, Joan E. Roberts states, “The removal of these wavelengths from ocular exposure will greatly reduce the risk of early cataract formation. If you prevent light from exciting endogenous or exogenous chromophores in the lens, or you block the damage of reactive oxygen species with antioxidants, you may prevent or retard cataracts from forming.”5
Retina
In young eyes, a significantly higher amount of UVR reaches the retina since the crystalline lens has not yet developed the proteins that absorb UVR and shield the retina from this high energy light exposure. Consequently, young eyes are at a higher risk of photochemical damage occurring in their retinal cells. The retina is susceptible to photochemical damage which occurs because of chemical (oxidative) reactions induced by absorption of high energy photons. The highest energy photons that reach the retina are from ultraviolet radiation. UV transmission reduces with age, but people in their teens, 20s and 30s still have significant amounts of UV reaching their retinas.
Digital Device Screen Emissions and Blue Light
Blue light product claims often imply a high level of protection for the retina.6 However, claims of retinal damage from screen use are unsubstantiated. Despite conflicting studies regarding the blue light emission levels from digital devices and their ability to produce harmful effects, and despite the fact that very limited protection is provided by clear blue filter lens products, interest in blue light has unfortunately eclipsed interest in the irrefutable UV threats to eye health.6 Simply put, the health risks from UV are real and well documented. Therefore, our communication with the patient regarding light protection must convey the higher level and immediate threat posed by UV radiation exposure.
Bringing Clarity to the Blue Light Buzz
The case for blue light hazards harming eyes exposed to digital device screens is tenuous at best.
Recently, there has been growing concern about visible blue wavelengths between 400 and 500nm – the spectral region associated with blue light hazard (BLH). Some studies have linked long term exposure to blue light in sunlight to macular degeneration. Other research has contradicted these claims, while many blue light studies have notable shortcomings.
Is Blue Light Media Hype?
Unfortunately, the media has misunderstood blue light’s potential eye damage risks. The University of Toledo showed, in a study, that blue light could damage the retina. However, the study exposed human cells in vitro to 445nm using a blue laser concentrated at only one wavelength, to examine the damage induced. While the findings made for sensationalist headlines, they were clearly not representative of real world conditions.
Never the less, many press outlets interpreted the study to mean that blue light from electronic devices can severely injure retinas. For example, a headline from Fortune Magazine stated, “Blue Light Emitted from Electronics Can Cause Accelerated Blindness, Study Finds.”7
If blue light has the potential to harm our retina, then natural outdoor light presents a far greater risk than any digital source. Natural sunlight produces blue light that is brighter and many orders of magnitude higher than any digital display, even when displays are on the brightest settings.
Given the current scientific evidence, the perceived long term eye health risk of blue light from digital devices is premature and likely overstated.
The debate and controversy over blue light will likely remain for a while, but we can confidently recommend UV protection based on proven well-established peer-reviewed scientific and clinical data. Eye health and light protection conversations can certainly include blue light, but first and foremost, we have a duty to warn and protect patients of the danger that UV poses to their eyes.
Current Ophthalmic Lens UV Standards
Exposure to UVR hazards can occur from artificial light sources such as welding arcs, tanning lamps, UV sterilisers and UV curing lamps. Although these sources can cause immediate damage, the acute effects are usually short lived and reversible. However, it is exposure to natural UVR outdoors that presents the greatest threat.
The highly respected World Health Organization defines the UVR spectrum as extending to 400nm.8 Ophthalmic lens industry standards organisations, however, are inconsistent in their definition of the UVR spectrum range (Figure 2).9
Figure 2
For example, the ISO ophthalmic lens standard (ISO 13666:2012 – ophthalmic optics – spectacle lenses – vocabulary) refers to an average solar daylight spectrum but defines the upper limit of UV radiation to be at 380nm.10 By this definition, 40% of solar UVR exposure on the earth’s surface is within a spectral band that is ignored by this standard (Figure 3). In contrast, the Australia/New Zealand sunglass standard (AS/NZS 1067:2003) for sunglasses and fashion spectacles, defines UVR as ending at 400nm.11 Higher levels of UV exposure exist for those living at, or near, the equator where the sun is closest to the earth.
Figure 3. Spectral band of solar UV exposure on Earth12
Figure 4. Human Crystalline Lens Transmission
Exposure rates vary with age, as illustrated in Figure 4. A portion of the UVR spectrum reaches the retina in a young person’s eyes that is largely absorbed by anterior structures of the adult eye. The very young have the highest level of UV transmittance to their retinas and therefore the highest exposure. Gradually, the transmittance of UV to the retina diminishes, but remember that any UV reaching the retina is damaging, and the damage is cumulative and irreversible. Certain medications and supplements increase the intensity of UVR, its damaging effects and the rate of damage. The mechanism for increasing damage is due to their photosensitising effects. According to an article in Nanobiomaterials in Antimicrobial Therapy (2016), “Photosensitisers are molecules that can be activated by light in order to generate reactive oxygen species (ROS) that can damage cell structures from microorganisms or from diseased mammalian cells leading to cell death”.13
Those who sunbathed while taking an antibiotic and suffered a severe sunburn, will have experienced the effects of photochemical damage from photosensitisers. Something as simple as aspirin is a photosensitiser, and many blood pressure drugs are as well. Both the skin and eyes are at a higher risk of harm from UVR when photosensitisers are applied to the skin or ingested. Knowing that circumstances that place our eyes and our patients’ eyes at higher risk of UV damage abound, it is incumbent upon us to ensure that every patient is armed with this information. We all deserve the opportunity to be pre-emptive in protecting our health, including our eye health.
Also, keep in mind that UV transmittance to the retina increases dramatically in those who have had a cataract removed and replaced with a clear intraocular lens (IOL). Although newer IOLs have some UV protection built in, they do not protect up to UV400nm. Additionally, this new influx of UV is impinging an aged eye that has already accumulated a lifetime of damage, making the retina even more susceptible to damage. Those with light coloured eyes, blue or green, are more susceptible to the harmful effects from UVA because of higher transmission levels that pose a threat for increased cancer risk.
UVR Exposure for Spectacle Wearers
The vast majority of UVR enters the lens from the front, making it vital to have a lens that prevents it from passing through to the eye.
However, four out of five spectacle lenses do not block 100% of UV up to 400nm from passing through the lens, including most polycarbonate lenses. Fortunately, new technology, such as Zeiss UVProtect lenses, are now able to provide significant protection from UVR exposure for the spectacle wearer.
In a recent peer reviewed study, UVR irradiance was measured using a specially designed mannequin to simulate real world conditions.14 In this study, 94% or more of UV was found to strike the front of the spectacles, while a maximum of 6% reached the eye from other angles, which were not blocked by the spectacles (Figure 5a and b). UVR irradiance was greatest when the mannequin faced toward the sun, likely due to the greater intensity of direct sunlight reflecting off spectacle frames and facial features of the mannequin. Some of the rearward UVR was found to miss the face and pass into the lens. Although you will hear that these rays will reflect into the eye only, a perfect UVR mirror could return all those rays to the face. The total UVR irradiation traveling through the front of the lens is up to 20 times larger than the UVR irradiation passing from behind the wearer.15
This is in stark contrast to the claims of one industry paper which states that a significant portion of hazardous UVR exposure to the eye (approximately 50%) is reflected from the back surface of spectacle lenses.16 The data in this paper is not only old and flawed, but it has, regrettably, helped foster a false sense of security in our industry that back coating UV anti-reflective coatings can significantly reduce UV exposure.
The repercussions of UVR exposure should be clear for the eye care professional and the spectacle wearer: for many wearers, the greatest potential exposure may occur when wearing clear lenses outdoors. Most of the UVR that can reach the eye and eyelids strikes the front of the spectacle lens first. It is therefore imperative for clear spectacle lenses to render it harmless; all of it, up to 400mm.
Figure 5a
Figure 5b
Clear Protection
The best way to protect our eyes is to provide sunglass level protection in a lens that blocks UV fully, up to 400nm, and to start protection at an early age.
For example, clear lenses with UV protection up to 400nm without any noticeable tint are effective because they filter UV in the substrate and therefore prevent its transmission through the lens and to the eye.
Zeiss, in particular, has closed this significant UV protection gap by including innovative UVProtect technology in all Zeiss clear plastic lenses. This technology provides the highest level of UV protection in a lens, by blocking UV wavelengths up to UV 400nm while maintaining clarity with no noticeable tint.3
Conclusion
The most popular clear spectacle lens materials do not completely block the most plentiful source of UVR – the solar spectrum between 350 and 400nm. Some ophthalmic lens standards ignore the hazard of UVR wavelengths longer than 380nm and up to 400nm, creating a UVR protection gap.6
Spectacle wearers are typically aware of some of the damaging effects of UVR, but many incorrectly think their lens materials or coatings already provide complete UVR protection. In many cases, their eye care professionals have been led to the same inaccurate conclusion.17
Ophthalmic prescription lens standards for UVR are derived from studies of damage caused by short high-intensity exposure to UVR to structures only in the eye itself. The eyelids are perhaps even more susceptible to UVR damage. The cumulative damage to the skin from low level exposure to UVR over many years is well documented, but many people will not apply sunscreen on their eyelids.18
Recent research suggests that the action spectrum used in some ophthalmic lens standards does not solely represent the risk to the eye itself and that further spectra should also be considered.3 It is worth noting that cosmetic and sunscreen industries all use the 400nm UV standard in the development of their skincare products.19
As we understand more about photo-aging and pre-cataract changes to the lens of the eye, it is becoming apparent that long wavelength UVR is more damaging than previously thought.
This damage may be amplified by medications or herbal supplements that increase photosensitivity.
All of this makes it imperative that lenses provide the highest level of UVR protection or UV400.
The light protection conversation must return to increasing awareness amongst patients of the eye health threat posed by UVR. The blue light conversation certainly deserves to occur, but it must be put in its proper place and be delivered from a more pragmatic perspective.
This article is sponsored by ZEISS.
Deborah Kotob, ABOM, an experienced optician and educator, is the director of education and training for the 20/20 Group in the United States of America. For the last 10 years, Ms Kotob has worked at Vision Ease as a staff trainer and ECP education facilitator. She is a master optician with more than 25 years’ experience in the optical industry, including frame and lens sales, and 10 years of experience in optical education and training. Prior to her position at Vision Ease, Ms Kotob owned and operated successful high-end optical boutiques.
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References
1. Ivanov, I., et al.,"UV-radiation oxidative stress affects eye health", Journal of Biophotonics, under revision
2. Roberts Joan E. Photobiology of the Human Lens. Fordham University, Department of Natural Sciences. photobiology.info/Roberts.html
3. Zeiss data on file. EN_20_200_02261
4. https://eyewiki.aao.org/Squamous_Carcinoma_of_the_Eyelid
5. Roberts Joan E., Ph.D. Ultraviolet Radiation as a Risk Factor for Cataract and Macular Degeneration. Eye Contact Lens. 2011 Jul;37(4):246-9. doi: 10.1097/ICL.0b013e31821cbcc9.
6. Zeiss data on file. EN_20_200_03251
7. Reints Renae. The blue light emitted from electronics can cause accelerated blindness, study finds. 15/08/2018 http://fortune.com/2018/08/15/blue-light-blindness-study/
8. www.who.int/uv/uv_and_health/en/
9. Rossi, Bryan. The invisible truth about UV. Canadian Eye Care Business Review https://eyecarebusiness.ca/uv-protection-we-can-all-do-more/
10. www.iso.org/standard/55784.html
11. www.arpansa.gov.au/understanding-radiation/radiation-sources/more-radiation-sources/sun-protection-sunglasses
12. www.zeiss.com/vision-care/int/about-us/newsroom/news-overview/2019/zeiss-uvprotect-protection-against-harmful-uv-radiation.html
13. Grumezescu, Alexandru Mihai. Nanobiomaterials in Antimicrobial Therapy Volume 6, Science Direct, 2016
14. Rifai,K., et al., Efficiency of ocular UV Protection by clear lens solutions, Biomedical Optics Express 9.4 (2018): 1948-1963
15. Rosenthal F., et al., "The effect of prescription eyewear on ocular exposure to ultraviolet radiation." Am. J. Public Health. (1986)
16. Behar-Cohen, Francine, et al. Ultraviolet damage to the eye revisited: eye-sun protection factor (E=SPF), a new ultraviolet protection label for eye wear. Clinical opthalmology (Auckland, NZ) 2014
17. www.mivision.com.au/2019/03/survey-highlights-ignorance-surrounding-uv-and-eyes/
18. www.ucihealth.org/blog/2019/05/eye-sun-protection
19. www.dermatest.com.au/Scientific/New%20Australian%20SPF%20and%20UVA.pdf