Relationships Between Preoperative Astigmatism and Corneal Optical Power, Axial Length, Intraocular Pressure, Gender, and Patient Age

Abstract

BACKGROUND: Preoperative astigmatism is likely to influence the outcome of cataract surgery, but it is only rarely considered in studies of cataract surgery outcomes. METHODS: As part of a population-based study of 5878 consecutive cataract surgeries performed from 1986 through 1990, I studied the relationship between preoperative astigmatism and corneal shape, axial length, intraocular pressure, gender, and age. RESULTS: The men had more against-the-rule astigmatism than the women, and the preoperative astigmatism shifted for both genders toward against-the-rule with age. Long eyes tended to have more with-the-rule astigmatism. Also, astigmatism deviated more from normal in both long and short eyes, and the with-the-rule astigmatism decreased with increasing intraocular pressure. Finally, I found that a second-degree polynomial model better described the relation between the axial lengths and keratometric powers better than a linear one. CONCLUSIONS: Axial length is related to the direction and amount of astigmatism. Because in the present study a second-degree polynomial described the relationship between the axial lengths and keratometric powers better than a simple linear regression, a polynomial model also probably should be used for calculating the power of the intraocular lens to be inserted.