Optic disc dimensions and cup-disc ratios among healthy South Indians: The Chennai glaucoma study

Purpose: To present optic disc and cup dimensions, cup-disc ratios (CDRs) and asymmetry among healthy South Indians, and their associations with ocular and systemic variables. Methods: A total of 623 healthy phakic participants of the Chennai Glaucoma Study underwent complete eye examinations including optic disc stereo-photography. Planimetry was performed under stereo-viewing conditions. The morphological type of cupping (no cups, steep cups, partly sloping and fully sloping cups) was identified based on a modification of the classification by Jonas et al. ¹¹ The associations of planimetric measures (optic disc area, cup area and vertical cup-disc ratio [VCDR]) with age, gender, height, intraocular pressure, refraction, astigmatism, axial length and corneal thickness as explanatory variables were examined. The associations of asymmetries in the above planimetric measures with age, gender and asymmetries of the above explanatory variables were examined. Results: Mean optic disc and cup areas were 2.82±0.52mm ² and 0.53±0.39mm ². Mean CDR was 0.36±0.18. Men had larger discs (P=0.03). Cup area and VCDR revealed significant associations with disc area (P <0.0001) and type of cupping (P<0.0001). Mean disc and cup area asymmetries were 0.19±0.16mm ² and 0.15±0.15mm ². Mean VCDR asymmetry was 0.07±0.08mm ². Cup area and VCDR asymmetries showed significant associations with disc area asymmetry (P<0.0001, both) and asymmetry in the presence or absence of physiological cupping, i.e. subjects with physiological cupping in one eye and no cupping in the other (P<0.0001, both). Conclusions: We present normative optic disc, cup and VCDR measures and asymmetries among healthy South Indians. We demonstrated the dependence of VCDR on the morphological type of cupping.