Purpose: In this article, we examine the relationship between corneal and refractive astigmatism (including with the rule, against-the-rule, and oblique astigmatism) in an adult population using power vectors.
Methods: Refractive and keratometric measures of astigmatism were conducted on right eyes of 105 white subjects aged 18 to 59 years. We performed a linear regression of refractive astigmatic error on corneal astigmatism, using the J0 and J45 components of the astigmatism.
Results: We obtained a statistically significant regression relationship between the corneal (C) and refractive (R) astigmatism for both J0 and J45 components, namely, RJ0 = 1.07 × CJ0 - 0.28; and RJ45 = 1.46 × CJ45 + 0.03. This results is a kind of generalized Javal rule for an adult population, because it is extended to include oblique astigmatism. We also found that the internal astigmatism is against-the-rule and uniform in our sample.
Conclusions: This vector-based approach is equivalent to the traditional Javal rule, but it has the ability to make predictions about oblique astigmatism, rendering it more general and more accurate.