Changes in macular layers in the early course of non-arteritic ischaemic optic neuropathy

To characterise the changes of the retinal layers in patients with acute anterior ischaemic optic neuropathy (AION), aiming to identify imaging markers for predicting the residual visual function.

This was a retrospective review of consecutive patients with unilateral AION from January 2010 to December 2013. We analysed affected eyes at baseline and 1 month later, compared to fellow healthy eyes. Utilising novel image analysis software, we conducted algorithmic segmentation in layers and division in early treatment of diabetic retinopathy study (ETDRS) quadrants of optical coherence tomography images of the macula. Pearson product moment regression analysis of retinal layer thickness and best corrected visual acuity (BCVA) in logMAR units and mean deviation of the SITA 24-2 visual field (VF) were carried out at the 1-month time point.

Twenty eyes from 20 patients were included and compared to 20 healthy fellow eyes. At baseline, we found a significantly increased mean thickness of the retinal nerve fibre layer (RNFL) of 42.2 μm (±6.7SD) in AION eyes compared to 37.9 μm (±4.2 SD) in healthy eyes (p = 0.002). The outer nuclear layer (ONL) was also significantly thickened at 96.6 μm (±7.2 SD) compared to 90.8 μm (±5.7 SD) in the fellow eye (p < 0.001). After 1 month, the RNFL and the ganglion cell layer (GCL) were thinned 17.7 % [to 31.2 μm (±6.4 SD), p < 0.001] and 19.3 % [to 66.5 μm (±7.0 SD), p < 0.001] compared to the contralateral eye. Additionally, the ONL remained thickened at 96.7 μm (±7.0 SD, p < 0.001). At baseline, we found a significant correlation between the ONL thickness and the VF (r = -0.482, p = 0.005) and the BCVA at discharge (r = 0.552, p < 0.001), indicating that a thicker ONL correlates with poorer visual function. The GCL thickness also correlates with the BCVA at discharge (r = 0.411, p = 0.02), where a thinner GCL predicts worse BCVA. At the 1-month time point, the GCL thinning was correlated with both the VF (r = 0.471, p = 0.005) and the BCVA (r = -0.456, p = 0.007), indicating worse visual function.

Changes in the thickness of different layers of the retina occur early in the course of AION and evolve over time, resulting in the atrophy of the GCL and RNFL. ONL thickening at baseline is associated with visual dysfunction. Thinning of the GCL after 1 month correlates with poorer VF and BCVA at 1 month after acute AION.