Evaluation of posterior astigmatism measured with Scheimpflug imaging.

PURPOSE Our aim was to assess the corneal power, axis, and age dependence of the anterior and posterior corneal surfaces with Scheimpflug imaging. METHODS Patients older than 10 years without a history of ocular surgery, corneal diseases, contact lens wearing, or severe dry eye were enrolled. Data regarding the anterior and posterior cornea were analyzed by means of Scheimpflug imaging (Pentacam HR). RESULTS The median age was 46.8 years (range: 10.0-90.3), and involved 827 eyes of 827 patients. Posterior corneal astigmatism was a median of -0.30 diopters (D) and exceeded 0.50 D in 12.56%. The ratio of the anterior-to-posterior corneal radius was a median of 1.217 (range: 1.021-1.402). The correlation between this ratio and age was significant (r = -0.219; P < 0.001). The correlation between anterior and posterior corneal astigmatism and age was significant. At the anterior surface, the ratio of with-the-rule astigmatism was 80.0% for the age range 10 to 20, decreasing to 36.0% for those aged over 81 years, whereas the ratio of against-the-rule astigmatism increased from 7.1% to 44.0%. At the posterior surface, the ratio of with-the-rule astigmatism was 94.3% for the age range 10 to 20 years, decreasing to 84.0% for those aged over 81 years, whereas the ratio of against-the-rule astigmatism increased from 1.4% to 8.0%. CONCLUSIONS The posterior cornea significantly influences corneal astigmatism. Its power value and orientation are much more stable with advancing age compared with anterior surface values.