Abstract
Abstract: :
Purpose: To examine the 5-year changes in spherical error and astigmatism in an older population. Methods: The Blue Mountains Eye Study examined 3654 residents aged 49+ years during 1992-94. Excluding 543 persons who died since baseline, 2335 (75.1%) attended follow-up exams during 1997-99. Both exams included a detailed eye assessment, with subjective refraction, performed according to the Beaver Dam modification of the ETDRS protocol. Cataract was graded using Wisconsin System. Spherical equivalent (sum of sphere + 1/2 cylinder) was used as the measure of refractive error. Change in myopia or hyperopia was indicated by a change in spherical power of at least 0.5D; change in astigmatism by a change in cylindrical power of at least 0.5D. Only phakic eyes with best-corrected visual acuity ≷20/40 were included. Results: After exclusions, 3701 eyes were available for analysis. Change in refractive error between the two eyes was highly symmetric; 72% participants had symmetrical changes when the difference between eyes was within 0.5D and over 91% for a difference within 1.0D. The 5-year change in spherical power was in a hyperopic direction for the younger age groups and in a myopic direction for older subjects, p<0.0001. The gender-adjusted mean change in refractive error in R eyes of persons aged 49-54, 55-64, 65-74 and 75+ at baseline was +0.41D, +0.30D, +0.05D and -0.22D, respectively. No significant gender differences were found for the mean refractive change. The magnitude of change was strongly related to baseline nuclear cataract severity; grade 4-5 was associated with a myopic shift (-0.33D, p<0.0001). Baseline refractive status also predicted the magnitude of refractive change. The mean age-adjusted change in refraction was +0.14D for hyperopic eyes, +0.32 for emmetropic and +0.15D for myopic eyes. The magnitude of change was related to the level of education and age of onset of myopia, but was unrelated to the presence of diabetes. The mean change in cylinder-power over the 5-year period was small, irrespective of baseline refractive status. The axis of astigmatism remained stable in most cases (64%), while 12% changed to "against the rule" and 11% to "with the rule". Conclusion: This report has documented refractive error changes in an older population. Our findings were similar to changes reported by the Beaver Dam Eye Study. The study confirms reported trends of a hyperopic shift before age 65 years and a myopic shift thereafter, associated with developing nuclear cataract.
Keywords: 542 refraction • 354 clinical (human) or epidemiologic studies: prevalence/incidence • 325 astigmatism