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 magnification-corrected OCT disc areas were respectively 1.849±0.343mm2, 1.809±0.285mm2 and 1.964±0.386mm2; the cup areas were 0.246±0.187mm2, 0.172±0.180mm2 and 0.469±0.332mm2. On HRT, the disc areas were 2.11±0.38mm2, 2.06±0.40mm2 and 2.16±0.42mm2; and the cup areas were 0.28±0.34mm2, 0.25±0.18mm2 and 0.48±0.32mm2. 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 ≤0.002), 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 eyes.
Conclusion: NAION patients have smaller cups and CDARs in both eyes compared to controls. A larger sample size is necessary to demonstrate if disc size affects the risk of developing NAION. The NAION eyes' OCT RNFLT had a better correlation with HVF than that measured by HRT.