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 ± 0.52 mm(2) and 0.53 ± 0.39 mm(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 ± 0.16 mm(2) and 0.15 ± 0.15 mm(2). Mean VCDR asymmetry was 0.07 ± 0.08 mm(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.

Neural rim characteristics of healthy South Indians: the Chennai Glaucoma Study.

PURPOSE: To report neural rim dimensions for South Indians and examine rim shape with relevance to clinical evaluation. METHODS: Healthy phakic participants (n = 623) of the Chennai Glaucoma Study with normal frequency-doubling perimetry underwent complete eye examinations including optic disc digital stereophotography. Planimetry was performed under stereoviewing conditions using custom software. Rim area, shape, and associations were examined. Rim area asymmetry was studied in a subgroup of 565 subjects. RESULTS: Mean neuroretinal rim area was 2.29 +/- 0.39 mm(2). Disc area (P < 0.001) and type of cupping (P < 0.001) were associated with rim area. Mean rim area asymmetry was 0.18 +/- 0.15 mm(2); 95% of subjects had asymmetry < 0.5 mm(2). Disc area asymmetry (0.359, P < 0.0001) and intraocular pressure (IOP) asymmetry (P = 0.004) were related to rim area asymmetry. On average, the inferior rim was thickest and the temporal was thinnest. Mean inferior by superior rim width was 1.18 +/- 0.17; 2.5 percentile, 0.9. Thirty-eight (7.1%) subjects had the superior rim thicker than the inferior rim, the occurrence of which was associated with disc torsion (P = 0.002) and male sex (P = 0.04). Of the clinically relevant rim width measures in glaucoma (i.e., inferior, superior, and temporal) the temporal rim was thinnest in 469 (87.8%) eyes. Horizontally oval disc shape (P < 0.0001), type of cupping (P = 0.006), and astigmatism (P = 0.001) were associated with the presence of thicker temporal than superior/inferior rims. CONCLUSIONS: The report provides hitherto unreported neural rim measurements among healthy South Indians. The ISNT rule (inferior rim thicker than superior rim, thicker than nasal rim, thicker than temporal rim) was violated in a significant minority. Physiological associations with such violations are described.