EyeNet Magazine



   
 
Clinical Update: Cataract
Back-and-Forth Controversy on Blue-Filtering IOLs
By Lori Baker Schena, PHD, Contributing Writer
Interviewing Deepinder K. Dhaliwal, MD, Bonnie A. Henderson, MD, and Martin A. Mainster, PHD, MD
 
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For cataract surgeons, it’s a given that presbyopia-correcting intraocular lenses necessitate more chair time with their patients. Yet instilling realistic patient expectations for the immediate future is only part of the story, according to Deepinder K. Dhaliwal, MD, associate professor of ophthalmology, chief of refractive surgery and director of the cornea service at the University of Pittsburgh. Long-term eye health is of equal importance, especially since Americans are living longer, she said. “When I first started regularly implanting the Crystalens accommodating IOL, I was concerned about the fact that the lens offered minimal if any UV protection. To help protect my Crystalens patients from potentially harmful UV rays, I made it a point to recommend that they wear UV-blocking sunglasses when venturing outside.”

But then data from the Beaver Dam and Blue Mountain studies, which implicated blue-light rays as a risk factor for age-related macular degeneration following cataract surgery, caught Dr. Dhaliwal’s attention. “I realized that UV light was not necessarily a threat to the patient’s eye health once the cataract was removed. Instead, blue light appeared to be more of an issue. And with the exception of one yellow-tinted lens on the market, the other lenses did not block the blue light.”

Dr. Dhaliwal added that while blue light has not yet been directly linked to AMD, “it made sense to offer patients retina protection.” For this reason, when counseling her presbyopia-correcting IOL patients, she now recommends amber-tinted sunglasses, which are designed to block blue light, as opposed to gray-tinted sunglasses. “It’s an issue that could easily be overlooked by busy surgeons, but it has become part of the postoperative protocol with my patients,” she said.

Dr. Dhaliwal’s concern about long-term retina health in cataract patients is shared by other ophthalmologists. It also mirrors one side of a larger issue currently being hotly debated in the ophthalmic community: Do the potential benefits of blue-filtering IOLs outweigh potential drawbacks?

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The Case Against Blue-Blocking IOLs

Martin A. Mainster, PhD, MD, is a professor of ophthalmology at the University of Kansas in Kansas City, as well as a physicist and author of more than 30 peer-reviewed articles on photoreception and photic retinal hazards. Dr. Mainster actually introduced the concept of the UV-protective IOL in 1978, but now he notes that “IOLs without UV-absorbing chromophores have been used safely and successfully for more than four decades. That’s why colorless UV-transmitting IOLs as well as colorless UV-blocking and yellow-tinted blue-blocking IOLs are used widely today.”

No cause to fear blue. He added that, in fact, “10 of the 12 major epidemiological studies show no link between environmental light exposure and AMD. Most AMD occurs in phakic adults over 60 years of age, despite senescent crystalline lens photoprotection far greater than that of blue-blocking IOLs. If light does play some role in AMD, then pseudophakes should wear sunglasses in very bright midday environments. Pseudophakes have the freedom to remove their sunglasses for optimal photoreception but not the yellow filters in their IOLs. Blue-blocking IOLs force cataract surgeons to choose fear of the unproven, largely failed phototoxicity-AMD hypothesis over light that patients need for their best possible circadian and dim light photoreception. Growing evidence shows that cataract surgery does not cause macular degeneration so blue-blocking IOLs won’t prevent it.”

Some proponents of blue-blocking IOLs point to a study by Nolan and colleagues investigating whether blue-filtering IOLs affect the density of macular pigment.2 (Macular pigment has been proposed as a protectant against AMD because it absorbs blue light at a prereceptoral level.) The study showed that pigment density increased with blue-blocking IOLs but remained stable with colorless IOLs, Dr. Mainster said, adding that this was “an odd result because the patients’ original crystalline lenses absorbed far more short wavelength light than their implanted blue-blocking IOLs. Also, the relationship between macular pigment and AMD is unproven, and any potential protective value of macular pigment probably lies in its biochemical rather than optical properties.”

The benefits of blue light. Dr. Mainster regards blue light as possibly vital to a number of physiologic processes, and interfering with it may have adverse effects. “Blue-blocking IOLs eliminate half of a pseudophake’s violet and blue light. These wavelengths provide 45 percent of scotopic, 83 percent of circadian and 94 percent of S-cone photoreception. It’s no wonder that blue-blocking IOLs have been shown clinically to reduce photopic luminance contrast, photopic S-cone foveal thresholds, mesopic contrast acuity and scotopic short-wavelength sensitivity,” he said.3

Dr. Mainster’s research with colleague Patricia L. Turner, MD, found that environmental illumination plays a key role in human health because blue-light sensitive retinal ganglion photoreceptors send essential information about environmental light to more than a dozen nonvisual brain centers. This information guides critical daily circadian rhythms, including metabolic homeostasis, sleep-wake cycles and the synthesis of hormones and neurotransmitters.

“Bright, properly timed light exposures profoundly influence human health and psychology,” he said. “In the morning, they facilitate transitioning human physiology from sleep to wakeful demands. In the daytime, they improve mood and decrease depression. Natural light increases cognition and work performance. Blue light accelerates learning. Age-related crystalline- lens yellowing reduces retinal violet and blue light illumination essential for circadian photoreception and dim light vision,” he said. “Thus, it’s no surprise that cataract surgery improves health as well as vision. Insomnia and depression, in addition to increased glare, may well prove to be relative indications for cataract surgery.”4

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The Case for Blue-Filtering IOLs

Discussions about the potential disadvantages of blue-filtering IOLs do not escape the attention of Bonnie A. Henderson, MD, assistant clinical professor of ophthalmology at Harvard University: The blue-filtering IOL is the primary lens she uses in her cataract practice, and her patients appear extremely satisfied with this choice. “Although I had never come across any clinical problems or complaints about the blue-light filtering IOLs, I had heard the criticisms and wanted to investigate whether there was any validity behind the claims. The last thing I wanted to do was cause harm to my patients so I decided to undertake a comprehensive literature review.”

No harm from blue-blocking. Dr. Henderson and her colleague, Kelly Jun Grimes, MS, reviewed 56 reports published between 1962 and 2009 that have relevance to blocking blue light transmission. The studies covered topics ranging from sleep disturbance, visual outcomes and cataract surgery to lens transmittance, sunlight exposure and macular disease. Their findings, which were published in the Survey of Ophthalmology, found that 91 percent of peer-reviewed reports concluded that there were no significant detrimental effects of blue-light filtering IOLs on different indicators of visual performance, including visual acuity, contrast sensitivity, color perception and photopic, mesopic and scotopic sensitivities.5 “While some researchers have been vocal in pointing out the potential concerns with these lenses, the vast majority of studies found that any potentially harmful effects on vision were not clinically significant,” Dr. Henderson said. “For example, while the literature shows some decreases in scotopic vision, when accounting for the removal of the aging crystalline lens, the overall effect is a large improvement in scotopic vision regardless of the color of the IOL.”

She added that in clinical studies, the blue-light filtering was well-tolerated, and there were no reports of altered night vision or insomnia. “This finding is important given the theoretical detrimental effects of blue-light filtering on night vision, as well on sleep regulation, melatonin and its effect on the circadian cycle.” The finding is particularly relevant, said Dr. Henderson, given the potential benefit of lowering the incidence or progression of AMD with blue-blocking IOLs.

Are blockers useful? Dr. Henderson stressed that her study did not look at whether the blue-light filtering IOLs are actually beneficial. And, in fact, previous to 2009, the studies were inconclusive.

However, a new study by Gray and colleagues, currently in press in Journal of Cataract and Refractive Surgery, found that patients with blue-light filtering IOLs performed significantly better under driving conditions with glare compared with similar patients who had clear IOLs. And Dr. Henderson noted the study by Nolan and colleagues showing that blue-filtering IOLs affected macular pigment density. 2 “This study demonstrated that patients wearing these lenses had an increase in pigment density, which may have a role in the prevention of AMD,” Dr. Henderson said. “While the observed connection between this increase in pigment density and a reduced risk of AMD development or progression should still be further studied, if it turns out there is a beneficial effect from blue-filtering IOLs, I want to give patients that advantage. In the meantime, it is obvious from the published literature that blue-light filtering IOLs are not harmful and may offer real advantages.”

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In Summary

Meanwhile, Dr. Mainster and colleagues believe that blue-filtering IOLs have not been shown to prevent AMD but do reduce the light needed for mesopic, scotopic and circadian photoreception. 3,6,7 Dr. Henderson and her colleagues see no harm posed by blue filters, at least in visual parameters, and feel that the possible protection against AMD is worth it. Their research on blue filters did not, however, establish protection against AMD by blue-light blocking, nor address some of Dr. Mainster’s nonvisual brain center concerns, like photoreception-enabled metabolic homeostasis and the synthesis of various hormones and neurotransmitters.

Dr. Mainster added that “Patients should not lose valuable visible light at a time in their life when they need it the most because of age-related pupillary miosis, photoreceptor loss and decreased environmental illumination. Clinical studies show that blue-blocking IOL filters adversely affect mesopic vision.”6 He said that cataract surgery can improve health as well as vision by increasing blue-light dependent circadian and rod photoreception.4 “If blue-blocking IOLs had been the standard of care for the past few decades, then colorless UV-blocking IOLs could be introduced now as the new ‘premium’ IOLs because they provide dim light and circadian photoreception 15 to 20 years more ‘youthful’ than blue-blockers.”1,2

The color of concern: blue or amber? For Dr. Dhaliwal, the growth in popularity of clear lens exchange, combined with the fact that patients are living longer, make it necessary to take the potential risk of AMD seriously. “If blue-blocking decreases the risk of macular degeneration, then we need to counsel our premium-IOL patients correctly,” she said. “For me, that means ensuring that my patients all understand the importance of wearing sunglasses outdoors, particularly amber-tinted lenses. Our responsibility does not end after we implant an IOL.”
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1 Mainster, M. A. Br J Ophthalmol 2006;90:784–792.
2 Nolan, J. M. et al. Invest Ophthalmol Vis Sci 2009;50:4777–4785.
3 Mainster, M. A. and P. L. Turner. Surv Ophthalmol 2010;55:272–289.
4 Mainster, M. A. and P. L. Turner. Sleep Med Rev 2010;14:269–280.
5 Henderson, B. A. and K. J. Grimes. Surv Ophthalmol 2010;55:284–289.
6 Wirtitsch M. G. et al. Ophthalmology 2009;116:39–45.
7 Mainster, M. A. and P. L. Turner. Ophthalmology 2011;118:1–2.
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Dr. Dhaliwal consults for Alcon. Dr. Henderson consults for Alcon and Ista Pharmaceuticals. Dr. Mainster consults for Abbott Medical Optics.

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To Decide, Read First

Dr. Mainster emphasized the importance of peer-reviewed reports, mentioning his editorial with Dr. Turner on this subject in the January 2011 Ophthalmology. He also suggested reading the Centers for Medicare and Medicaid Services’ analyses in the Federal Register, noting their conclusions in 2005 that “the relationship between blue light and AMD is speculative and not proven by available evidence” and in 2010 that blue-blocking IOLs “do not demonstrate substantial clinical benefit in comparison with currently available IOLs.”

Dr. Henderson agreed that ophthalmologists should scrutinize the published literature. “Reports on this topic, especially in support of blue-light filtration, continue to surface in peer-reviewed literature. For example, a recent article by Billy Hammond and colleagues (Hammond, B. R. et al. Clin Ophthalmol 2010;4:1465–1473) found that the filtering of blue light has distinct effects on visual performance by significantly lowering glare disability and improving the visibility of a target in the presence of glare.”

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