Characterization Of Anterior And Posterior Corneal Astigmatism And Factors Associated With With-The-Rule Posterior Corneal Astigmatism

To characterize anterior and posterior corneal astigmatism in a large patient sample and to identify the factors associated with with-the-rule posterior corneal astigmatism

Centro Oftalmológico Virgilio Galvis, Floridablanca, Colombia

Analytical cross-sectional study of an anonymized secondary clinical database including patients with ocular biometry performed by the IOL Master 700.

A total of 6059 eyes with biometric data (IOLMaster700) were included (mean age 65.5±16.9 years). Anterior corneal astigmatism was with-the-rule in 45.3% of the entire group, but in the over-80 group, the percentage of eyes with against-the-rule anterior astigmatism was 71.2%. The type of posterior corneal astigmatism was highly dependent on the type of anterior corneal astigmatism. When the anterior astigmatism was against-the-rule, the percentage of eyes exhibiting against-the-rule posterior astigmatism was 54.0%.  In patients aged 60–80 years and those over 80 years, the percentage of eyes with against-the-rule anterior corneal astigmatism that had against-the-rule posterior corneal astigmatism was only 57.6% and 42.3%, respectively.

This is important because many patients undergoing cataract surgery present with against-the-rule anterior corneal astigmatism, as they are usually over 60 years old, and therefore it would not be appropriate to assume that the vast majority of them have against-the-rule posterior corneal astigmatism, as the toric lens calculation nomograms—based solely on the measurement of anterior corneal astigmatism—do. Our findings suggest that it seems preferable to perform a direct measurement of posterior corneal astigmatism rather than using any nomogram that makes assumptions regarding this posterior astigmatism in patients who are to undergo cataract surgery with toric lenses.