Effect of optic disc size on correlation between Bruch's membrane opening-minimum rim width and peripapillary retinal nerve fibre layer thickness.

Abstract

To investigate the effect of optic disc size on correlation between Bruch's membrane opening-minimum rim width (BMO-MRW) and peripapillary retinal nerve fibre layer (RNFL) thickness from three scan circles. In this retrospective, observational study, non-glaucomatous eyes without visible RNFL defect or visual field loss were included. A total of 101 subjects were distributed into three groups based on disc size: group 1 (n = 26), small disc (disc area < 1.63 mm2); group 2 (n = 40), regular size disc (disc area: 1.63~2.43 mm2); and group 3 (n = 35), large disc (disc area > 2.43 mm2). All patients underwent standard ophthalmic examinations including confocal scanning laser tomography and spectral-domain optical coherence tomography. Global BMO-MRW was the thickest in group 1 (314.96 ± 60.38 μm, BMO area: 1.72 ± 0.45 mm2), followed by that in group 2 (259.03 ± 40.04 μm, BMO area: 2.29 ± 0.31 mm2). It was the thinnest in group 3 (236.74 ± 31.21 μm, BMO area: 2.91 ± 0.31 mm2; p < 0.001, Kruskal-Wallis test). Correlation between global BMO-MRW value and RNFL thickness was the strongest in group 3 (Spearman's rho = 0.656), followed by that in group 2 (rho = 0.572). It was the weakest in group 1 (rho = 0.147). There was no significant difference in global RNFL thickness by disc size from either the 3.5 mm, 4.1 mm, or 4.7 mm diameter scan circles (all p > 0.05). Correlation between BMO-MRW values and RNFL thickness differed significantly according to disc size. Thus, when we assess BMO-MRW in relation to RNFL thickness, disc size may need to be taken into consideration.