The aging effect on corneal curvature and the validity of Javal's rule in Hong Kong Chinese

Purpose. The current study compared the central corneal curvature and the r efractive error of Hong Kong Chinese to study the validity of Javal's rule. Methods. Subjects without corneal pathology were recruited at different age ranges. Their refractive error and the corneal curvature were measured and compared for the right eye only. Two instruments were used for the measure ment of corneal curvature including a conventional Bausch & Lomb (B&L) kera tometer and a computer-assisted videokeratoscope (TMS-1). Results. Subjects age ranged from 21 years to 77 years were recruited and w ere categorized into five groups according to age. The Bausch & Lomb kerato meter was found to provide corneal information similar to that from the TMS -1. The corneal astigmatism was found to change from with-the-rule to again st-the-rule with advancing age. The spectacle astigmatism followed a simila r trend. There was a hyperopic shift in the spherical component of the refr active error with aging as well. A regression equation: Spectacle astigmati sm = 0.93 (Corneal astigmatism) + (-0.58D x 90) was found, which is similar to the simplified Javal's rule. There was a shift of 1.03D in hyperopia (s pherical equivalent) for each decade. Conclusions. Both the corneal and spectacle astigmatism demonstrated a shif t from with-the-rule to against-the-rule with age. The simplified Javal's r ule is more suitable for predicting the spectacle astigmatism from corneal astigmatism in Hong Kong Chinese.