Non-arteritic anterior ischemic and glaucomatous optic neuropathy: Implications for neuroretinal rim remodeling with disease severity

Abstract

Purpose: Post-acute non-arteritic ischemic optic neuropathy (NAION) and glaucomatous optic neuropathy (GON) can be difficult to differentiate clinically. Our objective was to identify optical coherence tomography (OCT) parameters to help differentiate these optic neuropathies.

Methods: We compared 12 eyes of 8 patients with NAION and 12 eyes of 12 patients with GON, matched for age and visual field mean deviation (MD). All patients underwent clinical assessment, automated perimetry (Humphrey Field Analyzer II; Carl Zeiss Meditec, Dublin, CA, USA), and OCT imaging (Spectralis OCT2; Heidelberg Engineering, Heidelberg, Germany) of the optic nerve head and macula. We derived the neuroretinal minimum rim width (MRW), peripapillary retinal nerve fibre layer (RNFL) thickness, central anterior lamina cribrosa depth, and macular retinal thickness.

Results: MRW was markedly thicker, both globally and in all sectors, in the NAION group compared to the GON group. There was no significant group difference in RFNL thickness, globally or in any sector, with the exception of the temporal sector that was thinner in the NAION group. The group difference in MRW increased with increasing visual field loss. Other differences observed included lamina cribrosa depth significantly greater in the GON group and significantly thinner central macular retinal layers in the NAION group. The ganglion cell layer was not significantly different between the groups.

Conclusions: The neuroretinal rim is altered in a dissimilar manner in NAION and GON and MRW is a clinically useful index for differentiating these two neuropathies. The fact that the difference in MRW between the two groups increased with disease severity suggests distinct remodelling patterns in response to differing insults with NAION and GON.

Fig 1. Peripapillary RNFL and MRW in a NAION patient compared to GON.

Both patients had prominent superior greater than inferior visual field loss (greyscale; left). The peripapillary retinal nerve fibre layer (RNFL) thinning is prominent diffusely in the NAION case including temporally, whereas the thinning in the GON case is preferentially superotemporal and inferotemporal. The minimum rim width (MRW) grossly matches the peripapillary RNFL in the GON case. In contrast, the MRW is not thin, and is in fact, above average in the NAION case.

Fig 2. Lamina cribrosa depth.

(A) The lamina cribrosa depth (μm) was significantly greater in the GON (Glaucomatous Optic Neuropathy) group than the NAION (Non-Arteritic Anterior Ischemic Optic Neuropathy) group. An example pair of cases showing greater lamina cribrosa depth in the NAION (B) compared to the GON (C). The difference between the dashed line and yellow line (anterior lamina cribrosa) is the lamina cribrosa depth. Cyan arrows indicated the minimum rim width (MRW) measurement. The ILM is demarcated by the red line. Box and whisker plots show individual data, median, and interquartile ranges. ***denotes P < 0.001.

Fig 3. Thickness of central retinal layers.

The central retinal layers were thinner in the NAION (Non-arteritic Anterior Ischemic Optic Neuropathy) group compared to the GON (Glaucomatous Optic Neuropathy) group for the inner plexiform layer (IPL), inner nuclear layer (INL), and outer plexiform layer (OPL). There was no difference in the retinal nerve fibre layer (RNFL), ganglion cell layer (GCL), or outer nuclear layer (ONL). Box and whisker plots show individual data, median, and interquartile ranges. Correction was made for multiple comparisons using the Bonferroni method. *denotes P < 0.05 and **denotes P < 0.01.

Fig 4. Correlations of peripapillary RNFL and MRW thickness with visual field mean deviation.

(A) NAION and GON show diverging correlations with regards to minimum rim width (MRW). A more obvious separation occurs at more negative visual field mean deviations. (B) Similar positive correlation between peripapillary retinal nerve fibre layer (RNFL) thickness and visual field mean deviation for both the NAION and GON groups.