Characterization of the thinnest point of the cornea compared with the central corneal thickness in normal subjects.

INTRODUCTION: For ongoing progress in refractive surgery, exact knowledge about the anatomical properties of the cornea is useful. Thus, the aim of the study was to characterize the thinnest point of the cornea compared with the central corneal thickness in normal subjects and to investigate with regard to influencing factors such as sex, age, refraction, and intraocular pressure.

MATERIALS AND METHODS: The central corneal thickness and the thinnest point of the cornea were determined with the Orbscan II in 390 white normal subjects. Difference between the 2 eyes, influence of sex, and measuring repetition accuracy were tested for statistical significance with t tests, and the influence of age was tested with nonparametrical test methods.

RESULTS: In the right eyes, the mean central corneal thickness was 548 +/- 37 microm and the thinnest point 537 +/- 37 microm. In the left eyes, the mean central corneal thickness was 547 +/- 37 microm and the thinnest point 535 +/- 39 microm. The difference between the central corneal thickness and the thinnest point was found to be significant in both eyes in paired t test (P > 0.001). No influence of sex, refraction, and intraocular pressure on the thickness of the thinnest point of the cornea could be observed. The difference between central corneal thickness and thickness at the thinnest point was not subject to a statistically significant influence of age.

CONCLUSIONS: In the calculation of the residual corneal layer thickness in laser refractive surgery, the thinnest point of the cornea should form the basis.