Distribution of astigmatism as a function of age in an Australian population.

PURPOSE Astigmatism is a common cause of refractive error and is known to vary in prevalence with age. Although the search for genes associated with spherical refractive errors (especially myopia) has met with limited success, current efforts to identify genetic variants implicated in astigmatism development have been less rewarding. We aimed to assess the association between astigmatism and age to identify appropriate age cut-offs for maximizing power in genetic studies of astigmatism. METHODS We performed a cross-sectional analysis of right eye astigmatism data from four Australian-based eye studies comprising 3841 participants aged 5-90 years. Measurements were performed under cycloplegia using an autorefractor, and individuals with a history of cataract, refractive surgery or corneal pathology were excluded from the analysis. In addition to the magnitude and type (against-the-rule, with-the-rule, and oblique) of astigmatism, we calculated the vector components (J0 , J45 ) and evaluated the association of these outcome measures with age. RESULTS The magnitude of refractive astigmatism (RA) remained relatively stable [mean ± SD (-0.44 D ± 0.50)] until individuals reached the age of 50, thereafter increasing in average magnitude by approximately 1.00 D for those subjects aged 90. In contrast, corneal astigmatism (CA) remained relatively stable from childhood until the age of 80 (-0.76 D ± 0.61). The prevalence of clinically significant RA (≥1.00 D) increased with age and was highest in those aged >70 years [55.1% (47.2-62.7%)]. Age was significantly associated with RA in adults [odds ratio (OR) = 1.04 per 1 year, p < 0.001]. A weaker relationship was observed between CA and age (OR = 1.007 per 1 year, p = 0.02). CONCLUSIONS We have confirmed the previously documented association between RA and age. Our results indicate that most of the observed change occurs after the age of 50, providing a recommended cut-off for participants in genetic studies of this refractive condition.