Age-period-cohort effect on the incidence of age-related macular degeneration: the Beaver Dam Eye Study.
OBJECTIVE
To examine relationships of age, period, and birth cohort with the 5-year incidence of age-related macular degeneration (AMD).


METHODS
Population-based cohort study with 4 examination visits 5 years apart from 1988 through 1990, 1993 through 1995, 1998 through 2000, and 2003 through 2005.


METHODS
Two thousand nine hundred sixty-eight persons (6603 participant visits) and 3588 persons (8184 participant visits) 43 to 86 years of age at baseline contributing to the incidence of early and late AMD, respectively.


METHODS
Grading of stereoscopic fundus photographs using the Wisconsin Age-Related Maculopathy Grading System.


METHODS
Five-year incidence of early AMD.


RESULTS
While controlling for age, there was a lower 5-year incidence of early AMD in later rather than in earlier birth cohorts (odds ratio per increasing category, 0.70; 95% confidence interval, 0.62-0.78; P<0.001). This remained while controlling for smoking, blood pressure, and other related factors. There was no evidence for a period or birth cohort effect with late AMD.


CONCLUSIONS
Lower incidence of early AMD in more recent birth cohorts is likely the result of unmeasured risk factors for early AMD. Further study of possible unmeasured risk factors that may have caused this cohort effect may help to identify new modifiable risk factors for AMD. Diminishing incidence of early AMD in later birth cohorts would be expected to result in lower long-term estimates of future incidence of AMD than do current estimates that do not take this effect into account.
Klein
Ronald
R
Department of Ophthalmology and Visual Sciences, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin 53726-2336, USA. kleinr@epi.ophth.wisc.edu
Knudtson
Michael D
MD
Lee
Kristine E
KE
Gangnon
Ronald E
RE
Klein
Barbara E K
BE