Assessment of the anterior structures of eyes in a normal Northern Thai group using the Orbscan II.

Objectives: To evaluate the anterior structures of the eyes in normal Northern Thais include the corneal topography and thickness, as well as the anterior chamber depth (ACD) and the white-to-white (WTW) using the Orbscan II system.
Material and Method: One hundred and six eyes of 56 normal subjects were investigated using the Orbscan II. The simulated keratometry (SimK), astigmatism, corneal thickness, ACD and WTW were collected. The axial power maps as well as anterior and posterior elevation maps were read and categorized. Corneal thickness was measured in different regions and the pachymetry patterns were classified.
Results: The mean SimK was 44.18 (1.41)/43.30 (1.46) diopters (D) and the mean astigmatism was 0.93 (0.58) D. Symmetric bow tie was the most common axial power pattern in the anterior cornea (57.6%), followed by asymmetric bow tie (19.8%), irregular patterns (12.3%), round (9.4%), and oval (0.9%). Incomplete ridge (40.6%) and island (34%) were common elevation patterns observed in the anterior corneal surface, and island (92.5%) was the most common topographic pattern in the posterior. The thinnest point on the cornea had an average thickness of 512.49 (35) micron and was located at an average of 0.43 (0.24) mm from visual axis. In the pachymetry maps, round (47.2%) and oval (45.3%) were common patterns. The mean ACD and WTW was 2.79 (0.35) and 11.61 (0.36) mm, respectively.
Conclusion: The present study demonstrated the normal variations of anterior segment structures of the eyes in normal Northern Thais using the Orbscan II topography system. This information may be useful for comparison with further quantitative studies of various abnormal states.