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Freeman, Cataract Surgery and Age-Related Macular Degeneration
increase with time from cataract surgery, suggesting that such an effect (if it exists) likely occurs
soon after surgery.
A fourth explanation for the observed association between cataract surgery and late AMD
is the "light hypothesis"
7, 11
.
In this hypothesis, removal of the cataract newly exposes the retina
to certain wavelengths of light (or at greater intensity), damaging the retina and increasing the
risk of AMD
20
. Since most of the intra-ocular lenses currently in use have ultraviolet-B
blockers, the critical wavelengths are likely to be in the blue light region.
Further investigations
of this hypothesis would best be assessed by a randomized controlled clinical trial in which
critical or putative wavelengths are blocked.
Some eyes (1,803/23,380 eyes) could not be evaluated for AMD status, which could
cause concern for selection bias. However, when we examined the characteristics, eyes without
information on AMD status were from older people (66 versus 61 years old) and the eyes were
more likely to have had cataract surgery (8.1% versus 6.6%). Given the older age, it is likely
that the AMD rates of those eyes missing AMD status information would have been higher than
the rates seen in this study. Since we suspect the AMD rates to be higher and since we know the
rates of cataract surgery were higher in eyes missing AMD status, including these eyes in the
analyses would have likely only strengthened the results.
These analyses are cross-sectional in nature. Therefore, we are limited to identifying an
association between cataract surgery and AMD. Because we are unable to determine the
temporal relationship of cataract surgery and signs of AMD, we cannot declare that cataract
surgery increases the risk of AMD. Another limit to our analyses is the small number of cases of
AMD, particularly in the younger populations. For this reason, it is important to examine the
overall results and not just focus on the results that were statistically significant. Finally, the
