Age-related cataract in the Tibet Eye Study
T. S. Hu, Q. Zhen, R. D. Sperduto, J. L. Zhao, R. C. Milton and A. Nakajima
Peking Union Medical College Hospital, Beijing, China.
The Tibet Eye Study was designed to estimate the prevalence of age-related
cataract in Duilong-Deqing County, west of Lhasa, China (altitude, 4000 m).
Previous reports have suggested an unusually high prevalence of age-related
cataract in Tibet. A two-stage probability sample of persons aged 20 years
or older from the 35 townships of the county targeted 2884 persons for
inclusion in the study; 2665 (92.4%) were examined. Age-related cataract
was diagnosed when (1) visual acuity was worse than 6/12 (20/40) because of
nuclear or cortical (including posterior subcapsular) opacities, or (2)
aphakia associated with a history of age-related cataract was present in
either eye. The prevalence of age-related cataract among persons aged 20 to
39 years was 0.2%; among persons 40 years old or older, the prevalence was
11.8%. Cortical cataracts were by far the most common type of cataract
diagnosed. Age- and sex-adjusted prevalence in Tibet was 60% higher than
the prevalence in a similar, previously conducted study of 6951 person in
Shunyi County, northeast of Beijing (altitude, 50 m). A second, independent
slit-lamp classification of lens status was conducted in the Tibet Eye
Study using standard photographs previously described. Age-specific
cataract prevalence was similar with the two examination techniques.
Results from the Tibet Eye Study support previous suggestions of a high
prevalence of age-related cataract in Tibet.
