MyVisionTest News Archive
Jan 14, 2009
Blue Light and AMD: Myth or Reality?
Blue-blocking intraocular lenses (IOLs) that are implanted following cataract surgery block most ultraviolet (UV) radiation (wavelength <400 nm) and a substantial amount of violet (400 to 440 nm) and blue (440 to 500 nm) light. Their use was motivated by the hypothesis that retinal phototoxicity (photic retinopathy) from repeated environmental light exposures is a significant risk factor for age-related macular degeneration (AMD). UV-blocking IOLs that block most UV radiation and possibly some additional violet light. Proponents of blue-blocking IOLs argue that these lenses can reduce AMD risks without sacrificing any dim light or circadian photoreceptive benefits of UV-blocking IOLs that have been used successfully for more than two decades. We disagree.
A fundamental weakness of the phototoxicity-AMD hypothesis is its lack of epidemiologic confirmation despite over 20 years of careful investigation. While two large population-based studies did find an association between environmental light exposure and AMD, five other large population-based and four case-control studies failed to support this relationship. If there were a strong association between environmental light exposure and AMD, these large epidemiologic studies should have provided conclusive evidence. Additionally, AMD prevalence is not correlated with latitude as one might expect if environmental light exposure were a significant risk factor for AMD.
There is no evidence that normal environmental light exposure can injure the retina of persons that have undergone cataract surgery (known as pseudophakes). The Beaver Dam and Blue Mountain eye studies correlated late AMD with cataract surgery, but the Age-Related Eye Disease Study and recent Swiss, Chinese, and German studies found that pseudophakia was not a major risk factor for AMD. If a correlation does exist between cataract surgery and AMD, it is probably attributable to shared risk factors and/or the effects of intraocular surgery.
Ocular aging and inadequate environmental illumination limit nonvisual photoreception. Insomnia, depression, and memory problems are commonly associated with aging and also circadian disruption. Blue light is responsible for 55% of circadian photoreception and has been shown to increase alertness and cognition. Blue-blocking IOLs provide 27% to 38% less circadian sensitivity than UV-blocking IOLs. Cataract surgery with a UV-blocking IOL has been shown to decrease insomnia and daytime sleepiness.
Sensitivity spectra show that the ideal IOL for vision in dim environments and circadian photoreception should transmit as much blue light as possible. Blue-blocking IOLs sacrifice the optimal photoreception of UV-blocking IOLs for limited theoretical protection against the unproven phototoxicity-AMD hypothesis.
There is no clinical or experimental proof that normal light exposure causes AMD. The Centers for Medicare and Medicaid Services concluded that "the relationship between blue light and AMD is speculative and not proven by available evidence." We agree that the use of blue-blocking chromophores in IOLs to reduce AMD risks is not evidence-based medicine. Cataract surgery provides older adults with better conscious vision in bright and dim environments. Increasing blue light–dependent unconscious circadian photoreception extends the potential benefits of cataract surgery beyond image-based vision to improved health and longevity.
Read more...
Am J Ophthalmol 2009;147:8-10
Tags: AMD, cataract, sunlight
Blue-blocking intraocular lenses (IOLs) that are implanted following cataract surgery block most ultraviolet (UV) radiation (wavelength <400 nm) and a substantial amount of violet (400 to 440 nm) and blue (440 to 500 nm) light. Their use was motivated by the hypothesis that retinal phototoxicity (photic retinopathy) from repeated environmental light exposures is a significant risk factor for age-related macular degeneration (AMD). UV-blocking IOLs that block most UV radiation and possibly some additional violet light. Proponents of blue-blocking IOLs argue that these lenses can reduce AMD risks without sacrificing any dim light or circadian photoreceptive benefits of UV-blocking IOLs that have been used successfully for more than two decades. We disagree.A fundamental weakness of the phototoxicity-AMD hypothesis is its lack of epidemiologic confirmation despite over 20 years of careful investigation. While two large population-based studies did find an association between environmental light exposure and AMD, five other large population-based and four case-control studies failed to support this relationship. If there were a strong association between environmental light exposure and AMD, these large epidemiologic studies should have provided conclusive evidence. Additionally, AMD prevalence is not correlated with latitude as one might expect if environmental light exposure were a significant risk factor for AMD.
Ocular aging and inadequate environmental illumination limit nonvisual photoreception. Insomnia, depression, and memory problems are commonly associated with aging and also circadian disruption. Blue light is responsible for 55% of circadian photoreception and has been shown to increase alertness and cognition. Blue-blocking IOLs provide 27% to 38% less circadian sensitivity than UV-blocking IOLs. Cataract surgery with a UV-blocking IOL has been shown to decrease insomnia and daytime sleepiness.
Sensitivity spectra show that the ideal IOL for vision in dim environments and circadian photoreception should transmit as much blue light as possible. Blue-blocking IOLs sacrifice the optimal photoreception of UV-blocking IOLs for limited theoretical protection against the unproven phototoxicity-AMD hypothesis.
There is no clinical or experimental proof that normal light exposure causes AMD. The Centers for Medicare and Medicaid Services concluded that "the relationship between blue light and AMD is speculative and not proven by available evidence." We agree that the use of blue-blocking chromophores in IOLs to reduce AMD risks is not evidence-based medicine. Cataract surgery provides older adults with better conscious vision in bright and dim environments. Increasing blue light–dependent unconscious circadian photoreception extends the potential benefits of cataract surgery beyond image-based vision to improved health and longevity.
Read more...
Am J Ophthalmol 2009;147:8-10
