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The association between cataract surgery and progression of age-related macular degeneration still is unclear.
In light of this uncertainty, ophthalmologists can consider cataract surgery even in patients with AMD if the cataract affects vision and the patient's quality of life, Dr. Bressler added.
Globally, cataracts are one of the leading causes of blindness, with an incidence of 1.5 million cases per year in the United States alone. In addition, when untreated, AMD is a leading cause of blindness among people over 65 years of age in the United States.
Yet, there are questions as to the association between cataract surgery and the progression of AMD. According to Dr. Bressler, clinical evidence shows no increase in risk for progression to advanced AMD after cataract surgery.
"If you think the cataract is visually significant to a patient, you should consider removing the cataract," he said. "There is no clear evidence that AMD eyes are at clinically important greater risk for progression to advanced AMD following cataract surgery."
Basis for associations, progression risk
In explaining how these worries about cataract surgery accelerating AMD came to exist, Dr. Bressler explained that certain light exposure theories have come into play. Animal models have demonstrated that light toxicity can cause retinal damage, particularly low-wavelength blue light.
"There is a concern that if you remove the crystalline lens, you will permit more blue light to reach the retina, and therefore cause some maculopathy perhaps that is similar to AMD," he said.
"There is also a theory that acute conic inflammation occurs that can be induced by cataract surgery," Dr. Bressler said. "Perhaps this accelerates AMD. Indeed, there is basic scientific evidence to suggest that inflammation plays a role in the development of non-neovascular AMD."
Some information suggests that macrophage induction of angiogenesis or proinflammatory chemokines that may have angiogenic properties may be exacerbated by the inflammation caused by cataract surgery.
Other studies have shown an association between undergoing cataract surgery and progression of AMD, Dr. Bressler said. However, there are confounding variables in these population-based studies.
In addition, Dr. Bressler offered a caveat to these results: "Association does not mean causation."
AMD manifestations may have preceded the cataract surgery rather than being caused by it. The data from studies that have examined this question have been very inconsistent.
"Cataracts that have not been removed may obscure features of AMD," Dr. Bressler said. "You may have a lower recognition of AMD when the cataract is still in the eye. Maybe you cannot see geographic atrophy as well in these patients."
We don't know if the AMD that we see after cataract surgery is just initially recognized after cataract surgery or if it was there beforehand, Dr. Bressler explained.
"Maybe cataract surgery caused an increase of advanced AMD progression, but there are two alternatives," he said. "It's possible that the advanced features were there but we failed to recognize them. Then we take the cataract out and see them more easily."
It also is possible that these associations are just due to chance alone, Dr. Bressler continued.
"About 150,000 people with drusen who do not have cataract surgery go on to choroidal neovascularization per year," he said. "That does not mean that cataract surgery doesn't increase that risk, but that it will happen anyway."