FAMILIAL AGGREGATION AND PREVALENCE OF MYOPIA IN THE FRAMINGHAM OFFSPRING EYE STUDY

Objectives: To examine familial relationships for myopia among sibling s and the distribution of myopia in an adult population aged 23 to 78 years. Methods and Participants: Eye examinations were conducted in a cross-sectional study on the offspring of the Framingham Eye Study coh ort. Between 1989 and 1991, 1585 persons, the offspring of 1319 parent s, underwent refraction and were tested for best corrected visual acui ty. A person was considered myopic if at least one eye had a spherical equivalent refractive error of at least -1.00 diopter. Results: For b oth sexes, prevalence of myopia decreased with increasing age, from ab out 60% for ages 23 to 34 years to about 20% for ages 65 years and old er. Among men, both age and years of education were related to myopia. Among women, age was related to myopia, but years of education were n ot. Age-, sex-, and education-adjusted analyses, using the second-orde r generalized estimating equations approach, showed a strong associati on of myopia between siblings. The association between siblings decrea sed with increasing between-siblings age difference: the estimated odd s ratio was about 5 for an age difference of 2 years and half that for an age difference of 10 years. Conclusions: The relative importance o f genetic and environmental factors in explaining familial relationshi ps for myopia remains unclear. Nevertheless, the large increase in myo pia prevalence for more recent birth cohorts and the decrease in the s trength of the between siblings association for myopia with increasing between siblings age difference suggest an important role for environ mental factors in the cause of myopia.