Methodological problems in eye disease epidemiology.

The recent burst of activity in eye disease epidemiology, occasioned by increases in the number of ophthalmologists with training in epidemiology and of epidemiologists interested in eye diseases, makes this an appropriate time for taking stock of methodological problems in this field. In this review, based largely on the author's personal encounter with five large epidemiologic studies (2, 7, 19, 30, 39) of the four major chronic eye diseases (senile cataract, senile macular degeneration, diabetic retinopathy, and glaucoma), the following methodological areas are discussed: quality assurance; disease definitions and classifications; reproducibility of observations; visual acuity and visual field tests; needed technologic advances; study design of case-control studies and clinical trials; and data analysis (shall we count subjects or eyes?). The chief weakness of blindness registers has been inadequate evaluation of the extent of underregistration and of the variability of underregistration according to socioeconomic and racial subgroups. The Health and Nutrition Examination Survey (HANES), conducted by the United States Public Health Service, is a potentially valuable source of descriptive and analytic epidemiologic information on eye diseases. It is an examination of a large probability sample of the US population and includes various histories, clinical and laboratory examinations, and a nutrition interview. In the early 1970s, HANES included eye examinations, but these were curtailed because of inability to get ophthalmologists as examiners. In future HANES studies, efforts should be made to minimize the involvement of ophthalmologists in the eye examinations and to increase the use of nonophthalmologists (e.g., optometrists, technicians) and instruments (e.g., cameras, densitometers, automated perimeters). The validity and reliability of any new procedures will need to be determined. Studies may need to be limited to certain major eye diseases and conditions. Population glaucoma surveys have tended to omit partially or entirely the time-consuming visual field test. Yet, without this test, the diagnostic examination for glaucoma is incomplete. The automated perimeter, with which visual fields can be more quickly measured, promises to be an important screening tool for glaucoma prevalence and case-finding surveys. It should be field-tested for epidemiologic use. The absence of standardized disease definitions, without which comparisons between studies are uncertain, has been a handicap to epidemiologic research in eye disease. A first constructive step toward the development of disease definitions would be the development of disease classifications.(ABSTRACT TRUNCATED AT 400 WORDS)