Ability of the optical coherence tomography parameters to identify retinal nerve fibre layer defect in Indian eyes with mild glaucoma

• Thickness map performs better than deviation map and clock-hour map. • Angular width was <17° in all the eyes in which RNFL defect was missed. • Sensitivity and specificity of thickness map was 100% and 98% respectively. • Sensitivity and specificity of deviation map was 96% and 95% respectively. • Sensitivity and specificity of clock-hour map was 90% and 95% respectively. To compare the diagnostic ability of thickness, deviation and clock-hour map of spectral domain optical coherence tomography (OCT) to detect retinal nerve fibre layer (RNFL) defect in mild glaucoma. Cross sectional study Eyes with mild glaucoma and well defined photographic RNFL defect were included as cases and eyes with normal optic nerve head were included as controls. Fundus photograph and spectral domain OCT optic disc cube scan was performed in all the eyes. Thickness map, deviation map and clock-hour map of OCT were assessed for the presence of RNFL defect. Image J was used to calculate the width of the RNFL defect. 127 eyes were recruited in each group. OCT RNFL thickness map was able to identify the RNFL defect in all the 127 (100%) eyes, whereas deviation map was able to identify in 122 (96%) eyes and clock-hour map in 114 (90%) eyes. Average width of RNFL defect was 21⁰ (± 5.9). The width of the RNFL defect was <20° in all the eyes in which RNFL defect was missed by both deviation and clock-hour map. Narrow angular width of RNFL defect was the only risk factor for missing RNFL defect in both deviation and clock-hour map. Among the control eyes thickness map showed RNFL thinning in 3 (2.4%) eyes, deviation map in 6 (4.7%) eyes and clock-hour map in 7 (5.5%) eyes. Thickness map performs better than deviation map and clock-hour map in identifying RNFL defect in eyes with mild glaucoma.