EyeNet Magazine >> Cataract


Cataract

Blue-Blocking IOL Makes Its Debut

by Laura J. Rongé, Contributing Writer

Can IOLs that block blue-wavelength light help prevent age-related macular degeneration? Some ophthalmologists are betting that they can, based in part on intriguing results from laboratory studies.

And this summer, the FDA approved Alcon’s AcrySof Natural IOL (SB60AT), a single-piece, foldable acrylic IOL that filters both ultraviolet light and blue light.

But the ultimate outcome remains to be seen. Until the results of long-term prospective trials come in, the jury is out as to whether blue-blocking IOLs are an example of marketing getting ahead of the science—or whether they will follow their UV-blocking predecessors into widespread acceptance.

How It Works
Alcon’s blue-blocker IOL has been designed to mimic the light transmission of the natural human lens. “With aging, the crystalline lens normally takes on a yellowish color that filters blue light,” said Helga P. Sandoval, MD, research instructor at the Magill Research Center for Vision Correction at the Medical University of South Carolina, Charleston.

The new IOL is identical to Alcon’s current AcrySof IOL (SA60AT) with the exception of a proprietary yellow chromophore that is bonded to the acrylic material. “This chromophore blocks much of the light in the blue wavelength from passing through the lens,” said Robert J. Cionni, MD, medical director of the Cincinnati Eye Institute.

In an unpublished study, the UV and visible light transmission of the AcrySof Natural IOL was compared to that of four standard IOLs: the AcrySof MA60BM (Alcon), CeeOn Edge 911A (Pfizer), Phacoflex II SI40NB (AMO) and Sensar AR40E (AMO). Using spectrophotometry (Shimadzu UV-1601PC), researchers measured three of each lens type, then looked at the average transmission value for each, said Paul H. Ernest, MD, associate clinical professor of ophthalmology at Wayne State University, Detroit, and in private practice with TLC Laser Eye Center in Jackson, Mich.

The study found that most current IOLs filter light transmission only in the UV spectrum (that is, light in the wavelength range of 400 nanometers and below), Dr. Ernest reported, and they transmit most visible light above 400 nm, including the blue light between 400 and 500 nm.

In contrast, the AcrySof Natural IOL transmits a spectrum of visible light that mimics that of the natural human lens of a 53-year-old person without a cataract, up to approximately 450 nm. “It transmits all aspects of white light, but it blocks 20 percent to 80 percent of the wavelengths between 400 and 500 nm,” Dr. Ernest said.

Why Block Blue Light?
Since the early 1970s, researchers have published reports suggesting that exposure to blue-wavelength light might cause retinal changes similar to those observed in AMD, Dr. Sandoval noted.

For instance, the Chesapeake Bay Waterman Epidemiologic Study found a link between advanced AMD and long-term exposure to blue-wavelength or visible light, Dr. Cionni noted.¹

And in the laboratory setting, John Marshall, PhD, in England, Janet Sparrow, PhD, at Columbia University, and others have accumulated evidence suggesting that blue-wavelength light may damage the retina by contributing to the development of free radicals in the retina.^2,3 One theory that has emerged from their research is that lipofuscin (a by-product of retinal pigment epithelium metabolism) begins to accumulate in patients older than 50. Lipofuscin, which “is not removed by our macrophages,” Dr. Ernest said, “contains a molecule called A2E that absorbs blue light. This causes it to become charged and in turn charges the surrounding oxygen, which sends off electrons, or free radicals, that can damage the retinal pigment epithelial cells.”

Theoretically, then, filtering some of the blue light might reduce the formation of these free radicals. And if you take that theory far enough, instead of waiting until the free radicals form and then trying to block their effect on the cells, why not block the absorption of blue light and thus inhibit the production of free radicals in the first place?

But it’s a long way from the bench to the bedside—and much more research is needed to show whether and how a blue-blocking IOL might affect either development or progression of AMD. As Dr. Ernest pointed out, “Many people with macular degeneration still have their crystalline lenses in their eyes. Lifestyle, diet, smoking, genetics—these also have a lot to do with AMD.”

As it happens, Oliver D. Schein, MD, professor of ophthalmology at Johns Hopkins’ Wilmer Eye Institute, is organizing a large, prospective multicenter study to compare patients with blue-blocking IOLs and those without, as well as patients taking antioxidants compared with those not taking them. One group of patients will receive antioxidants plus blue-blocking lenses; a second will receive neither treatment; and the two remaining groups will receive either antioxidants or blue-blocking IOLs. The goal is to enroll some 50,000 patients, who will be followed for a long period of time, Dr. Ernest reported. “That will be the definitive study. Several large groups, including ours, have agreed to participate in it,” he said.

Results to Date
Alcon’s multicenter trial of the blue-blocking IOL in the United States involved 297 patients who were randomized to receive bilateral implantation with either the AcrySof Natural IOL or the AcrySof IOL with UV absorption only.

Patients underwent standard phacoemulsification and in-the-bag IOL implantation, and the second eye surgery was done 30 to 60 days thereafter. Clinical data were collected four to six months later.

The study found that the yellow chromophore incorporated into the AcrySof Natural lens had no negative impact on vision, Dr. Cionni said, noting that visual acuity, color perception and contrast sensitivity were specifically evaluated.

In visual acuity results, there was no statistical difference in the percentage of eyes achieving corrected 20/20 vision. One year after surgery, most eyes had BCVA of 20/40 or better. In color perception, there was no loss or change as assessed using the Farnsworth 100-hue test. There was some concern that the yellow chromophore might affect color vision, as yellow sunglasses do, Dr. Ernest noted, but no significant differences were found between the two IOL groups.

There was no loss or change in contrast sensitivity as tested with the VectorVision CSV-1000E at 120 to 180 days after the second eye surgery. The two IOL types showed similar results at a series of spatial frequencies under both photopic and mesopic lighting conditions, Dr. Ernest reported.

Surgical Outcomes
More aspects of the blue-blocking IOL to consider at this point:

Surgical ease. The AcrySof Natural IOL is easy to implant using the Monarch II injector, Dr. Sandoval said. Moreover, because the surgeon and assistant can see the Natural IOL more easily, loading and injection becomes easier, Dr. Cionni added.

Outcomes. Surgical outcomes to date, including posterior capsular opacification and YAG laser rates, are comparable to those seen with the AcrySof UV-blocking IOL. “We have had three eyes out of 40 that required posterior capsulotomy one year after surgery,”  Dr. Sandoval said. “We have not found any disadvantage or limitation for the use of this lens. There are no known contraindications at this time.”

Patient preference. “It may be that some patients will be happier with their color perception with a blue-blocking IOL,” commented Samuel Masket, MD, clinical professor of ophthalmology at the University of California, Los Angeles, and in private practice in Century City, Calif. “Patients often complain of cyanopsia with a traditional IOL, particularly after removal of nuclear cataracts, which absorb much of the blue end of the visual spectrum.”

Dr. Masket also noted that he has reviewed articles that demonstrate improved contrast sensitivity with a blue-blocking IOL. However, he cautioned, “As for protecting macular function, there’s no evidence that there’s a one-to-one relationship, as far as I know.”

________________________________
Drs. Cionni, Ernest and Sandoval participated in Alcon’s clinical trials of the AcrySof Natural IOL. Dr. Cionni also is a consultant for Alcon but has no equity interest in Alcon and no specific financial interest in this particular product. Dr. Masket has no related financial interest.

________________________________
1 Taylor, H. R. et al. Arch Ophthalmol 1992;110(1):99–104.
2 Sparrow, J. R. et al. Invest Ophthalmol Vis Sci 2000;41:1981–1989.
3 Sparrow, J. R. et al. Invest Ophthalmol Vis Sci 2003;44:2245–2251.