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Lisbon, Portugal—Blue-blocking IOLs, which recently have been promoted as being vision protecting, may not be doing the job.
Lisbon, Portugal-Blue-blocking IOLs, which recently have been promoted as being vision protecting, may not be doing the job.
Martin Mainster, PhD, MD, FRCOphth, outlined his arguments against the use of blue-blocking IOLs to protect against age-related macular degeneration (AMD) at the European Society of Cataract and Refractive Surgeons meeting in Lisbon, Portugal.
There are two classic types of retinal phototoxicity, namely, blue-green photic retinopathy and ultraviolet-blue (UV-blue) photic retinopathy, Dr. Mainster explained. Blue-green phototoxicity has an action spectrum that is similar to scotopic sensitivity. No IOL, including blue-blockers, provides significant protection against it.
UV-blue photic retinopathy causes solar and operating microscope maculopathy; its action spectrum increases with decreasing wavelength similar to that of lipofuscin, one of its primary mediators.
Is there a link?
Thus far, there is no certain link between AMD and light.
"Six of the eight major epidemiologic studies found no such correlation," Dr. Mainster stated and added that while light may be involved in AMD in some people, AMD is a complex disorder affected by many factors other than light, such as nutrition, smoking, and genetics. Dr. Mainster is Luther Fry Professor and vice chairman, department of ophthalmology, University of Kansas Medical School, Kansas City, KS.
The action spectrum of UV-blue phototoxicity is known, along with the transmittances of IOLs, crystalline lenses, sunglasses, and hypothetical UV??blocking filters, according to Dr. Mainster. He recommended the use of UV??blocking filters in a 1986 article1 because "phototoxicity increases markedly for lipofuscin in violet light, it peaks there for cytochrome oxidase and porphyrins, and macular xanthophyll's protection falls off rapidly in the violet." Violet wavelengths range from 400 to 440 nm and the blue range is 440 to 500 nm.2
Dr. Mainster offered some interesting comparisons. The crystalens (eyeonics, Aliso Viejo, CA) provides 150% less UV-blue photoprotection than conventional UV-only-blocking IOLs, he reported; in comparison, yellowish UV?blocking IOLs provide about 40% better UV-blue photoprotection than a UV-only-blocking IOL, about the same as the UV?? filters he recommended in 1986. However, the blue-blocking IOLs provide about 50% less UV-blue photoprotection than sunglasses, according to Dr. Mainster.
"More significantly, blue-blocking IOLs provide 20% less UV-blue photoprotection than Boettner & Wolter's 53-year-old crystalline lens," he added.
"Most AMD occurs in people over 60 years of age, so 53-year-old crystalline lenses don't prevent AMD. Thus, if light is a significant risk factor in macular degeneration, then the Boettner & Wolter data used to design blue-blocking IOLs show that they can't protect you from AMD," he said.
Blocking violet, transmitting blue
Dr. Mainster said that the common practice of blocking UV radiation with IOL chromophores makes good sense because UV is responsible for 67% of UV-blue phototoxicity but doesn't provide any useful scotopic vision. Violet causes another 18% of UV-blue phototoxicity but provides only 10% of scotopic vision. In contrast, blue light causes only 14% of UV-blue phototoxicity but provides 35% of scotopic vision.
"Blue light is much more important for scotopic and lower mesopic vision than for photopic vision. Scotopic sensitivity and dark adaptation decline with aging in everyone independent of lens yellowing, which increases the risk of falls, hospitalization, and death," Dr. Mainster emphasized.