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Donald O. Mutti, Karla Zadnik; Age-Related Decreases in the Prevalence of Myopia: Longitudinal Change or Cohort Effect?. Invest. Ophthalmol. Vis. Sci. 2000;41(8):2103-2107.
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purpose. The prevalence of myopia shows a decline with age in cross-sectional
studies. This pattern may represent an increase in the prevalence of
myopia in younger generations, possibly through increased exposure to
near work, or an intrinsic age-related decline in myopia prevalence.
Data were analyzed from published studies to determine which of these
two alternatives better explains the data: a cohort effect of changing
prevalence by decade or a longitudinal effect of changing prevalence as
a function of age.
methods. Prevalence data were taken from three studies conducted in the late
1980s and compared with those obtained indirectly from a national
survey conducted in the early 1970s. The prevalence of myopia was then
plotted as a function of age and year of birth.
results. The pattern of change in the prevalence of myopia as a function of age
was consistent across all studies when data were scaled relative to the
prevalence of myopia at age-range midpoints from 44.5 to 49.5 years.
The pattern of change was not consistent as a function of year of
birth. When the data were scaled relative to the prevalence of myopia
among those with years of birth from 1940 to 1942 and plotted by year
of birth, results from the early 1970s were offset from those of later
studies by approximately 18 years.
conclusions. The decline in the prevalence of myopia in older adults between the
early 1970s and the late 1980s can be better explained by age than by
year of birth. The prevalence of myopia appears to decrease because of
an intrinsic age-related decrease in the amount of an individual’s
myopia rather than because of a cohort effect of increasing prevalence
over time. The hypothesis that increasing environmental exposures to
near work in recent decades have changed the prevalence of myopia is
not supported by this analysis.
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