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

ABSTRACT

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 J0 represents the power of orthogonal astigmatism. Positive values of J0 indicate with-the-rule astigmatism, whereas negative values indicate against-the-rule (ATR). RESULTS: In this cross-sectional investigation, J0 represented the power of orthogonal astigmatism, and multivariate regression revealed that both J0 and corneal J0 (cJ0) declined with increasing age (both P < 0.001). In a longitudinal investigation spanning 5 years, the mean amounts of change (Δ) in J0 and ΔcJ0 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 ΔJ0, 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.