The morphology of the optic nerve head in two representative South-East Asian populations
Purpose: 1. To evaluate techniques of optic disc analysis in two population-based glaucoma surveys in South-East Asia. 2. To use these techniques to assess the normal distribution of optic disc characteristics in a Chinese and Thai population (currently unknown), and to compare with other ethnic groups. Methods: Optic disc data was obtained from 470 subjects aged >50 years from the Rom Klao glaucoma survey of Thailand, and 929 subjects aged >40 years from the Tanjong Pagar glaucoma survey of Singapore, using clinical biomicroscopy and a novel planimetric method involving stereo-photographs. Exclusion of subjects with an abnormal visual field test &/or an occludable angle &/or intraocular pressure (IOP) >97.5th percentile in either eye, resulted in 'normal' datasets of 292 Thai and 622 Singapore subjects. A sub-study using the Heidelberg Retina Tomograph-II (HRT) was conducted with 143 Thai subjects. Results: Systematic differences in disc parameter measures were found between pbiomicroscopy, planimetry and HRT. Mean planimetric disc area (DA) and neuroretinal rim area (RA) were similar in the two studies. No gender differences in DA and RA were found after multiple variable analysis. RA was unrelated to age in both studies. DA was positively correlated with AL, height and corneal thickness. RA was significantly lower in those with a history of migraine. The 'normal' biomicroscopic cup/disc ratio (CDR) distribution was similar between the two studies (median, 0.4 97.5th percentile=0.7), with CDR increasing with increasing disc size. Conclusions: The inter-correlation of disc parameters and the relationships between parameters and biometric variables were similar to those reported in Caucasians. The distribution of CDR was very similar to that found in several ethnic groups. Other parameters, such as neuroretinal rim configuration, were different. This research should assist clinicians, epidemiologists and diagnostic instruments in the judgment of normality of a given optic disc in these populations.