Posterior corneal astigmatism can be incorporated into toric IOL selection

Since before the turn of the 20th century, we recognized that there was a mismatch between anterior corneal astigmatism and refraction, although we were unable to pinpoint the cause. However, a new look with the aid of modern technology has shown us that posterior corneal astigmatism, or PCA, is also a significant player in the overall picture.In 2009, Ho and colleagues published a study of 493 subjects comparing the keratometric corneal astigmatism with the total corneal astigmatism derived by double-angled vector analysis of both corneal surfaces with the Pentacam (Oculus). They reported that in 28.8% of eyes, total corneal astigmatism differed from anterior corneal astigmatism by more than 0.5 D and that, overall, PCA reduced total corneal astigmatism by an average of 13.4%.