Quantitative assessment of optic nerve head morphology and retinal nerve fibre layer in nonarteritic anterior ischaemic optic neuropathy with optical coherence tomography and confocal scanning laser ophthalmoloscopy

Background/aims: To compare the optic disc parameters between patients with non-arteritic anterior ischaemic optic neuropathy (NAION) and normal controls, using optical coherence tomography (OCT) and Heidelberg Retinal Tomograph III (HRT), and to evaluate the structure-function relationship in NAION eyes. Methods: Both eyes of 22 patients with typical unilateral NAION of >= 6 months' duration and 52 eyes from 52 randomly selected normal subjects underwent Humphrey visual field (HVF) examination and measurement of optic disc and retinal nerve fibre layer thickness (RNFLT). Results: For the NAION-affected eyes, NAION fellow eyes and normal controls, the ocular magnification-corrected OCT disc areas were respectively 1.849 (SD 0.343) mm(2), 1.809 (0.285) mm(2) and 1.964 (0.386) mm(2); the cup areas were 0.246 (0.187) mm(2), 0.172 (0.180) mm(2) and 0.469 (0.332) mm(2). On HRT, the disc areas were 2.11 (0.38) mm(2), 2.06 (0.40) mm(2) and 2.16 (0.42) mm(2); and the cup areas were 0.28 (0.34) mm(2), 0.25 (0.18) mm(2) and 0.48 (0.32) mm(2). On both OCT and HRT, the cup areas and cup-disc area ratios (CDAR) of both eyes of NAION patients were significantly smaller than controls (p <= 0.01), but the disc areas were not (p >= 0.21). There was a significant correlation between HVF mean deviation and OCT RNFLT (r = 0.44, p = 0.04) but not with HRT RNFLT (p = 0.30) in NAION-affected eyes. Conclusion: NAION patients have smaller optic cups and CDARs in both eyes compared with controls. A larger sample size is necessary to demonstrate if disc size affects the risk of developing NAION. The NAION-affected eyes' OCT RNFLT correlated with HVF mean deviation but the HRT RNFLT did not.