Cross-Sectional and Longitudinal Investigation of the Power Vector in Astigmatism: The Yamagata Study (Funagata)

Purpose: To investigate how age and other factors affect astigmatism in Japanese adults over a period of 5 years. Methods: We included 512 Japanese participants who had undergone systemic and ophthalmological examinations both in 2005-2007 and in 2010-2012 in Funagata town, Yamagata, Japan. Astigmatism was evaluated using power vector analyses, where J(0) represents the power of orthogonal astigmatism. Positive values of J(0) indicate with-the-rule astigmatism, whereas negative values indicate against-the-rule (ATR). Results: In this cross-sectional investigation, J(0) represented the power of orthogonal astigmatism, and multivariate regression revealed that both J(0) and corneal J(0) (cJ(0)) declined with increasing age (both P < 0.001). In a longitudinal investigation spanning 5 years, the mean amounts of change (Delta) in J(0) and Delta cJ(0) were -0.045 +/- 0.308 and -0.072 +/- 0.278, respectively. This confirmed an ATR shift with increasing age in most individuals. The age-divided distribution of the magnitude of differences indicated that older age was associated with a larger astigmatic change over a 5-year period in both the cornea and the entire eye. Using multivariate logistic regression, we observed that older age at baseline was a risk factor for low Delta J(0), indicating a large shift toward ATR astigmatism. Conclusions: We confirmed that a refractive and keratometric shift toward ATR astigmatism occurs with aging. Older age at baseline was also associated with a larger magnitude of astigmatic changes over the subsequent 5 years.