effects of various risk factors on myopia progression

background: myopia has different prevalence rate worldwide and there is controversial points about its environmental risk factors. the prevalence of myopia in medical interns atshirazmedicalschool and its probable risk factors were studied.   method: in this retrospective cross-sectional study, three hundred interns (7 th -year medical students) at shiraz university of medical sciences were examined by auto refractometer and subjective refraction. we also administered a questionnaire to evaluate the age of the onset of myopia, the power of the first spectacles, and its power in the first year of medical school, parental refractive error, prematurity, mean amount of time spent for studying, sleeping, and tv watching per day among myopic students and a comparable control group.   results: ninety-two out of 300 (31%) interns had myopia over 0.5 diopters with similar age, sex, time spent for sleeping and studying as 88 randomly selected non-myopic controls. parental myopia was reported in 54% of cases and 25% of controls (p<0.05). 60% of myopic interns had more than 0.75 diopters of progression during medical school years with similar age, sex, and time spent for sleeping and studying as 40% with less than 0.75 diopters of progression. mean age of onset of myopia was 17.00±2.88 years with mean initial amount of -0.96±0.45 diopters in former subgroup, but in the latter subgroup, these were 13.84±2.99 years and -1.37±1.40 diopters, respectively (p<0.05).   conclusion: those students with myopia progression during medical study had later onset with less amounts of initial myopia than those without progression during the same period. iran j med sci 2006; 31(4): 204-207.   keywords ● myopia ● myopia progression ● nearwork