Does cataract surgery increase the risk of vision loss in people with age-related macular degeneration (AMD)? This question is explored in the February issue of Ophthalmology, the journal of the American Academy of Ophthalmology.
Age-related macular degeneration (AMD) and cataract are leading causes of visual impairment in the United States. Both are related to aging, and they share other risk factors, but it has been unclear whether a direct causal link might be involved. Several large epidemiological studies had raised concern that cataract surgery might accelerate AMD progress and threaten vision. To address this concern, Emily Y. Chew, MD, of the National Eye Institute, and colleagues analyzed data for a cohort of participants in the Age-Related Eye Disease Study (AREDS). This cohort is the only large prospective study in which the severity of AMD was documented before and after cataract surgery and which included more than five years of in-depth participant follow-up.
AMD causes changes in the retina, the light-sensitive tissue that focuses images at the back of the eye, and severe AMD leads to loss of central vision. Cataract is cloudiness or opacity in the eye's lens that interferes with the clear focus of images on the retina.
AREDS researchers concluded there was little evidence that cataract surgery had a negative effect on progression to advanced AMD. "These data may provide some reassurance to patients with AMD who are considering cataract surgery," Dr. Chew said.
The primary purpose of the AREDS multicenter controlled randomized clinical trial was to assess whether antioxidant and mineral supplements affect progress to advanced AMD and development of cataracts. The cohort study included 4,577 participants (8,050 eyes) aged 55 through 81 at enrollment; it compared the risk of advanced AMD in patients who had cataracts removed versus the risk for those who did not have the surgery. All participants took either antioxidant/mineral supplements or placebos. Study eyes were examined every six months over five or more years. One analysis compared AMD progression in matched pairs of eyes, where one eye had cataract surgery after baseline but before developing advanced AMD, and the paired eye did not have cataract surgery. Matched pairs were determined based on similar risk factors for AMD, assigned antioxidant or placebo treatment, baseline AMD category, person's age, and other factors. Results of the matched pair analysis and of two other standard analytical models revealed no consistent pattern of accelerated AMD progression after cataract surgery.
Several factors may explain the divergent conclusions reached by AREDS and the earlier studies. The most likely cause would be that earlier studies had unintended biases or confounding variables. Also, techniques of cataract surgery and lens replacement have changed over time, and AREDS participant surgeries were performed more recently than those tracked in the combined-population studies. A significant number of subjects in earlier studies did not have lens replacement after cataract extraction, while AREDS participants were likely to have had ultraviolet-B light blocking lenses inserted, which may have protected their maculae and decreased AMD risk.
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