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Editors Selection IGR 17-4

Anatomical Structures: Deep ONH structures in NTG

Comment by Chris Leung on:

67189 Comparison of the Deep Optic Nerve Head Structure between Normal-Tension Glaucoma and Nonarteritic Anterior Ischemic Optic Neuropathy, Lee EJ; Choi YJ; Kim TW et al., PLoS ONE, 2016; 11: e0150242

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Lee and colleagues compared the anterior lamina cribrosa surface depth (ALCSD) and prelaminar tissue (PT) thickness among 21 non-arteritic anterior ischemic optic neuropathy (NAION) patients, 42 normal-tension glaucoma (NTG) patients and 42 healthy subjects and showed that the ALCSD was greater and the PT thickness was smaller in NTG patients compared with NAION patients after matching the severity of optic nerve damage between the groups. Although the results highlight the differences in the pathophysiology between NAION and glaucoma, and indicate the relevance of ALCSD and PT thickness measurements in the discrimination between NAION and NTG, the data should be interpreted with reference to the potential limitations in the study design. As most NAION patients have small optic cups, it is not surprising to observe a small ALCSD in NAION. In fact, ALCSD was not only smaller in the NAION patients (390.1 µm) compared with the NTG patients (494.2 µm), but also compared with the normal subjects (427.3 µm) although the difference was not statistically significant. Using only three horizontal B-scans and three radial B-scans for measurements of ALCSD and PT thickness, respectively, local changes of lamina cribrosa depth and PT thickness consequential to NAION or NTG would be missed.

As most NAION patients have small optic cups, it is not surprising to observe a small ALCSD in NAION

Further, eyes with NTG had a longer axial length than the other groups and it is unclear if the differences in ALCSD and PT thickness between NAION and NTG would be explained by the difference in refractive errors (tilted optic disc configuration is not uncommon in eyes with myopia). Differentiation between glaucomatous from non-glaucomatous optic neuropathies can be challenging in clinical practice. It is hopeful that optical coherence tomography can augment the diagnostic precision for detection of different forms of optic neuropathies.

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