Objectives: To evaluate the characteristics of the cornea in myopic patients.
Material and Method: A retrospective study of 420 eyes in 210 patients who visited the Excimer Laser Surgery Clinic at Siriraj Hospital, Mahidol University from January 1999 to June 2002 was conducted. All cases that were eligible for myopic refractive surgery were included in the present study. A preoperative ocular examination was done in a fashionable method, including manifest refraction and Orbscan Topography to evaluate corneal thickness, corneal curvature and corneal diameter. Statistical analysis was performed to identify the characteristics of the cornea in the patients.
Results: The mean age of the patients was 31.66 + 7.77 years (ranging from 16-51). The mean manifest refraction (spherical equivalent) was -4.9 + 2.29 diopters (ranging from -0.50 to -13.75). The mean corneal diameter (white to white) was 11.60 mm + 0.37 mm (ranging from 10.8-12.9). The thinnest point of the cornea varied from 409 to 597 microns (mean = 522.55) and located mostly in the infero-temporal quadrant of the eye (23.69% in the right and 32.05% in the left). The mean curvature of the corneal was 44.6 + 13.8 diopters (ranging from 39.05-47.65). The mean corneal astigmatism was 1.34 + 0.71 diopters and 93.96% were with the rule astigmatism. Positive angle kappa was found in 408 eyes (97%) but all cases were within a 0.5 mm horizontal and 0.3 mm vertical radius from the pupillary axis.
Conclusion: Characteristics of the cornea in Thai myopic patients were demonstrated in the present study. Most of the cornea showed with the rule astigmatism with positive angle kappa and the thinnest point located at the infero-temporal quadrant.

Keywords: Cornea, Myopia, Thickness, Curvature