Corneal and refractive astigmatism in adults: a power vectors analysis

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.

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.

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.

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.