A model of spectral filtering to reduce photochemical damage in age-related macular degeneration.

Background/purpose: Cumulative sunlight exposure and cataract surgery are reported risk factors for advanced age-related macular degeneration (AMD). Laboratory studies suggest that accumulation and photochemical reactions of A2E (N-retinylidene-N-retinylethanolamine) and its epoxides, components of lipofuscin, are important in AMD. To relate this data to the clinical setting, we modeled the effects of macular irradiance and spectral filtering on production of A2E and reactive oxygen intermediates (ROIs) in pseudophakic eyes with a clear or "yellow" intraocular lens (IOL) and in phakic eyes.

Methods: We calculated relative changes of macular irradiance as a function of light (390 to 700 nm) intensity, pupil size, age, and lens status, and modeled resulting all-trans-retinal concentration and rates of production of A2E-related photochemicals and photon-induced ROIs in rods and retinal pigment epithelium (RPE). We compared these photoproducts following cataract surgery and IOL implantation with and without spectral sunglasses to normal age-related nuclear sclerotic lens changes.

Results: Following cataract and IOL surgery, all-trans-retinal and lipofuscin photochemistry would theoretically increase average generation of 1) A2E-related photochemicals, 2) ROI in rods and 3) ROI in RPE, respectively, 2.6-, 15- and 6.6-fold with a clear IOL, and 2.1-, 4.1- and 2.6 fold with a yellow IOL, but decrease approximately 30-, approximately 20- and 4-fold with a vermillion filter sunglass and clear IOL compared to an average 70 year old phakic eye.

Conclusion: Sunglasses that strongly decrease both deep blue light and rod photobleaching, while preserving photopic sensitivity and color perception, would provide upstream protection from potential photochemical damage in subjects at risk for AMD progression after cataract surgery.