The anterior and posterior corneal surfaces flattened and the anterior-to-posterior corneal curvature ratio decreased after radial keratotomy, a study found.
“This finding invalidates the standard keratometric index and thus has relevant implications for intraocular lens power calculation in RK eyes,” the study authors said.
IOL power calculation after RK can result in postoperative refractive surprises stemming from radius and IOL power errors and keratometric index error, they said.
The retrospective study included 29 eyes of 29 patients with a mean age of 46.3 years who underwent RK. A control group included 71 unoperated eyes.
A Pentacam rotating Scheimpflug camera (Oculus) was used to measure anterior and posterior corneal curvature radii at the 3-mm optical zone. The Gaussian optics formula was used to calculate total corneal power based on the Pentacam measurements.
Study results showed that the mean anterior corneal radius was 9.54 mm and the mean posterior corneal radius was 8.54 mm. Both radii were significantly higher than the 7.81 mm and 6.4 mm in the control group (P < .0001).
The mean anterior-to-posterior corneal curvature ratio was 1.22 in the control group and 1.12 in the study group; the difference was statistically significant (P < .0001).
Mean corneal flattening was 33.44% in the posterior corneal curvature and 22.15% in the anterior corneal curvature.
Data showed that the mean keratometric index was 1.3319 in the study group and 1.3281 in the comparator group; the between-group difference was statistically significant (P < .0001).
Regression analysis bore out a significant linear relationship between number of radial incisions and flattening of both corneal surfaces (P < .0001), the authors said.