Blue light-blocking IOL design helps protect RPE cells

Editor's Note: In the following article, Janet R. Sparrow, PhD, presents the results of a tissue culture study in which the blue light-absorbing design of one IOL was shown to protect retinal pigment epithelial cells from the damaging effects of light. In another report, Martin A. Mainster, PhD, MD, FRCOphth, contends that an IOL that filters blue light provides minimal protection against acute UV-blue retinal toxicity and limit scotopic vision.

New York-The AcrySof Natural IOL (SN60AT, Alcon Laboratories) has the ability to attenuate blue light-mediated cell death, according to results of a cell culture system study comparing several IOLs.

"By absorbing blue light, the AcrySof Natural IOL shields retinal pigment epithelium (RPE) cells that have accumulated the aging lipofuscin fluorophore A2E from the damaging effects of light," said Janet R. Sparrow, PhD, senior author of the study.

She and her colleagues constructed a cell culture system that allowed them to compare the ability of several IOLs to protect A2E-laden RPE from blue light damage.

"There is now a lot of evidence that the chromophores in retinal epithelial cells that are responsible for blue light damage themselves are fluorophores that accumulate with age and in some diseases and constitute the lipofuscin of the cell," Dr. Sparrow said. "We studied cells that had accumulated one of the lipofuscin fluorophores, a chromophore called A2E.

"Protecting the RPE is important in macular degeneration, both in older individuals and in the macular degeneration of juvenile onset-Stargardt's disease-because it is fairly well accepted that it is the death of the RPE cells that leads to the loss of photoreceptor cells and then impaired vision. Attention needs to be paid to the RPE, and there is considerable evidence that these cells are particularly susceptible to blue light damage," she continued.

A comparison study Dr. Sparrow's study of blue light-absorbing IOLs and RPE was published in the April 2004 issue of the Journal of Cataract and Refractive Surgery. IOLs compared in the study were the Alcon AcrySof Natural and AcrySof (SA60AT), the AMO Sensar (AR40e) and ClariFlex, and the Pfizer CeeOn Edge 911A. All but the AcrySof Natural block only UV light.

During testing, each IOL was applied to the undersurface of a culture well and centered over a light path. The cells were exposed to blue light (430 nm ± 30 [SD], 8 mW/cm²), green light (550 nm ± 10 nm, 8 mW/cm²), or white light (246 mW/cm²) over a 0.8- × 8.5-mm field.

To obtain a visual representation of IOL protection, 1-mm diameter disks were cut from the center of the IOL using a trephine blade. The IOL disks were positioned on the undersurface of the well, which was then irradiated (430 ± 30 nm, 16 mW/cm²) from below.

In a set of three experiments using a fluorescence assay to label the nuclei of nonviable cells, researchers found that 41.1% ± 4.1% of the A2E-laden cells in a field of illumination became nonviable after blue light exposure in the absence of an IOL. Placement of the AcrySof Natural IOL in the center of the light path reduced transmission of the 430-nm light by approximately 50% and reduced cell death by 80% (p < 0.001) compared with irradiation in the absence of an IOL.

When the AcrySof, Sensar, ClariFlex, and CeeOn Edge IOLs were placed in the light path, the frequency of nonviable cells was similar (p > 0.05) to cell death in the absence of an IOL. Modest declines in cell death observed with these IOLs were due to small reductions in light transmission (~5%) that were measured.