Normative data of optic nerve head in Thai population by laser scanning tomography: Siriraj study.

OBJECTIVE: To study the normative values of topographic optic disc parameters in a Thai population. MATERIAL AND METHOD: Two hundred and six eyes of 103 normal subjects aging from 30-80 years were studied Thirteen topographic disc parameters were analyzed by confocal scanning laser ophthalmoscope using Heidelburg retina tomography (HRT II). The average value of two eyes in the same subject was used as the unit of statistical analysis, and then the normal values and means were statistically calculated at 95% reference interval (95% RI). Ethnic differences of the calculated optic nerve topography were compared with previous studies. The relationship of age, intraocular pressure (IOP), central corneal thickness (CCT), and optic disc parameters were assessed by Pearson correlation. RESULTS: Mean values with 95% RI of all 13 parameters were analyzed Whole parameters except cup volume demonstrated normal distribution. Mean value (95% RI) of disc area in normal Thai people was 2.67 mm2 (1.96, 3.71) which was larger than Caucasian people. Ethnic differences in topographic optic disc parameters were found among Thai and other races including Asians, Caucasians, African-Americans, and Hispanics. The results also revealed that age, IOP, and CCT had no significant relation to all optic disc parameters. CONCLUSION: Thai people had a larger optic disc area than Caucasians. There are marked differences of topographic optic nerve parameters among different ethnic groups. These differences need to be taken into account when evaluating glaucomatous optic neuropathy and when comparing results of studies completed among population of different ethnic and racial origins.