The use of blue-blocking or violet-blocking intraocular lenses remains a subject of debate. While most ophthalmologists agree that blocking certain wavelengths of light in addition to ultraviolet light is advantageous for patients, they do not agree on the exact wavelengths to filter for maximal protection and optimal vision. Some believe that filtering blue light up to 500 nm is best for patients, while others believe that filtering too much blue light might compromise visual performance and that only violet light (400 to 440 nm) should be filtered.
The human crystalline lens protects the retina from hazardous ultraviolet light (200 to 400 nm); however, when this lens is removed during cataract surgery or refractive lens exchange, the retina is left unprotected, and the eye is at greater risk of incurring phototoxic damage. For this reason, most surgeons agree that it is important for IOLs to block UV light. There has been much debate, however, about the importance of filtering blue wavelength light.
The interest in filtering blue light in addition to blocking UV light is motivated by the concern that phototoxicity from environmental light exposure can induce uveal melanoma proliferation or accelerate age-related macular degeneration.1,2
Why Filter Blue or Violet Light?
Studies evaluating the harmful effects of environmental light exposure have yielded conflicting results. It has been established that acute exposures to blue light can cause retinal damage. In contrast, the effect of chronic, long-term exposure to blue or violet light has not been determined.
According to Martin Mainster, PhD, MD, "The relation between chronic light exposure and AMD is difficult to prove because of 1) the possibility that light is not a significant cause of AMD; 2) the difficulty of accurately estimating cumulative light exposure retrospectively; and 3) factors such as variable genetic susceptibility that obfuscate weak correlations."
Two large population-based studies have found an association between chronic light exposure and AMD,3,4 while four other large studies have not.5-8 Interestingly, one study described the first positive association between light exposure and macular degeneration, but a later study conducted by some of the same authors found no significant correlation.
In 1993, Australian researcher Hugh Taylor, MD, and colleagues studied the relationship between exposure to sunlight and senile cataract, AMD, pterygium and climatic droplet keratopathy in 838 watermen who worked on the Chesapeake Bay.3 Using detailed histories, ocular exposure was estimated for three bands of visible radiation: 400 to 450 nm (violet); 400 to 500 nm (blue); or 400 to 700 nm (all visible). Ocular exposure was also estimated for UV-A and UV-B. Compared with age-matched controls, watermen with advanced AMD had significantly more exposure to blue or visible light during the preceding 20 years. These data suggested that high levels of exposure to blue or visible light may cause ocular damage, especially later in life.
In 2001, Dr. Taylor and colleagues studied the risk factors and associated population attributable risk for age-related maculopathy (ARM) and AMD in Australians aged 40 years and older.6 The study included more than 4,700 people and found that the risk factors for AMD were: age, smoking cigarettes for longer than 40 years; and ever taking an angiotensin-converting enzyme inhibitor. The study concluded that the only modifiable risk factor for ARM and AMD was smoking.
"Results from phototoxicity experiments have been used as a rationale for blue-blocking IOLs, but acute retinal injuries and AMD are entirely different phenomena," says Dr. Mainster, who is a professor of ophthalmology at the
Because the consequences of chronic light exposure on the retina are unclear, some ophthalmologists believe that it is best to err on the side of caution and filter blue or violet light after cataract surgery.
"If we have the potential to reduce the risk of progressive retinal disease by using a blue-light filtering lens, and there is no downside to using the lens, why would we not want to provide this potential protective benefit for our patients?" asks Robert J. Cionni, MD, medical director of the Cincinnati Eye Institute, in Ohio.
How Much Is Enough?
If a surgeon believes that blocking some visible light may be beneficial to patients, he must then decide whether to filter only violet light or both violet and blue light. Alcon (AcrySof Natural) and Hoya (AF-1) have developed lenses that filter both blue and violet light, while Bausch & Lomb (SofPort AO lens with Violet Shield Technology) has developed a lens that filters only a small amount of violet light.
When choosing between blue-filtering and violet-filtering lenses, it is important to understand which wavelengths of light cause the most damage. According to Dr. Mainster, phototoxicity progressively increases as wavelength decreases, so UV is more hazardous than violet, which is more hazardous than blue light.
Some ophthalmologists believe that blocking blue light provides the best protection. "[Janet] Sparrow's study2 shows that the compound A2E found in lipofuscin is the main culprit in cell damage with exposure to blue light," Dr. Cionni says. "A2E is activated maximally when exposed to blue light with a wavelength of 441 nm. So, if we do not filter the wavelengths at and around 441 nm, we are not providing the necessary protection. And, therefore, filtering violet light only will not be as beneficial."
Others believe that violet-blocking lenses provide adequate protection and that blue-blocking lenses go too far. They believe that blocking this broad spectrum of light negatively affects visual performance.
What Effect on Visual Performance?
Dr. Mainster and Louis D. Nichamin, MD, believe that blue-light filtering lenses have a downside. "Violet light is potentially phototoxic, but it has little visual importance," Dr. Mainster says. "Blue light has relatively little phototoxicity, but it's vital for scotopic and circadian photoreception. If light is a factor in AMD, sunglasses should be worn in brilliant environments, but sunglasses can always be removed for optimal photoreception."
Dr. Nichamin notes that there have been reports that blue-blocking lenses have some attenuation of vision and contrast sensitivity under low-light conditions.9,10 "Common sense says that wearing a pair of yellow-tinted glasses at night could diminish one's vision," he says. Another issue is color perception. "Testing in this area may or may not have been carried out to the needed level," adds Dr. Nichamin, who is in private practice at the Laurel Eye Clinic in
He believes that it is best to be cautious and block the harmful portion of the light spectrum without using a deeply yellow-colored implant. According to Dr. Nichamin, the blocking agent in a violet-filtering lens does not discolor the lens optic as much as a broad blue-light filtering IOL.
"We'd like to err on the cautious side, but we don't want to negatively affect patients' vision in low-light conditions either," he says. "Someone may be able to pass a gross color differentiation test with a blue-blocking lens, but he may or may not have the same ability for subtle color discrimination and appreciation that patients might have with a clearer lens. The idea is to have a safe blocking agent of the dangerous portion of the light spectrum in everyone. We just need to identify the best blocker. To me, the violet option makes the most sense."
Others disagree, suggesting that filtering blue light offers the best protection, with no downside. In fact, Dr. Cionni has implanted the AcrySof Natural in more than 10,000 patients without a single problem with vision. "In addition," he says, "there are now several well-run prospective clinical studies clearly demonstrating that blue-light filtering IOLs do not cause a decrease in color vision, contrast sensitivity or night vision.11-13 I have yet to see any clinical study that demonstrates any negative effect of using a blue-light filtering IOL."
"My patients are thrilled with the quality of their vision," he adds. "A clear lens (UV-filtering only) lets in more light than the human crystalline lens does, even in childhood. When a UV-blocking only lens is implanted, patients say that the whites are so white that they look blue. The reason they are saying that is that their retina is receiving a lot more blue light than it ever has."
In fact, he believes that a UV-filtering clear lens lets in an abnormal amount of blue light. "The idea behind a blue-light filtering lens is not to block out high degrees of blue light. It is to filter blue light out to the level of a normal, noncataractous lens," he adds.
He notes that, in addition to potentially reducing the risk of developing or slowing the progression of AMD, blue-light filtering lenses also have the potential to reduce the risk of uveal melanoma.1
James P. McCulley, MD, chairman of the department of ophthalmology at the University of Texas Southwestern Medical Center in
Dr. Cionni agrees. "The clinical evidence showing that there is no downside to these lenses is overwhelming, and I believe that it would be wrong for a physician not to include blue-light filtering lenses in the list of options he or she gives a patient," he adds.
The Food and Drug Administration clinical trial found that there was no difference between the AcrySof Natural lens and the AcrySof single-piece lens regarding visual acuity, color perception or contrast sensitivity under photopic and mesopic conditions. Additionally, patients in both groups were given a quality-of-life questionnaire regarding color perception, driving ability and other vision-specific tasks, and both groups demonstrated an improvement over baseline.
What Impact on Quality of Life?
Dr. Mainster says that "blue-blocking IOLs provide 20-percent less protection than 53-year-old crystalline lenses that don't prevent AMD. Insomnia and depression increase with aging, and blue light is vital for unconscious retinal ganglion photoreception that mediates circadian photoreception. Cataract surgery is most patients' best chance to overcome natural aging and improve their circadian rhythmicity and vision in dim light."
However, Dr. McCulley notes that the blue-blocking IOLs filter out far less light than cataractous lenses. "To propose that having an IOL to filter some light is going to cause major sleep problems and depression does not make sense, because most cataract patients are not depressed and sleep-deprived, and they receive far less blue light than patients with blue-filtering IOLs," he adds.
Dr. Cionni adds, "Blue-light filtering IOLs allow about the same amount of blue light to reach the retina as does the normal, noncataractous crystalline lens of a 20- to 40-year-old person. To say that placing such an IOL will cause circadian rhythm dysfunction implies that every normal person over 20 years of age would have such dysfunction."
Dr. Mainster is a consultant for Advanced Medical Optics. Dr. Nichamin is a consultant for Bausch & Lomb. Drs. McCulley and Cionni are consultants for Alcon.
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