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Editors Selection IGR 9-4

Anatomical Structures: Computer-Assisted Retinal Layer Assessment

Comment by Augusto Azuara Blanco & Paul McCann on:

75979 Analysis of inner and outer retinal layers using spectral domain optical coherence tomography automated segmentation software in ocular hypertensive and glaucoma patients, Cifuentes-Canorea P; Ruiz-Medrano J; Gutierrez-Bonet R et al., PLoS ONE, 2018; 13: e0196112

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Due to the high proportion of retinal ganglion cell bodies and axons concentrated in the macula, spectral domain optical coherence tomography (SD-OCT) macular parameters have received attention as potential biomarkers in the detection of early glaucoma. A meta-analysis reported that full thickness macular parameters have similar or slightly inferior diagnostic accuracy compared to circumpapillary retinal nerve fiber layer (cRNFL) parameters.¹

However, improved technology has led to better retinal segmentation and there is now interest in the investigation of the diagnostic utility of segmented layers of the macula. Cifuentes- Canorea et al. investigated the diagnostic performance of Early Treatment Diabetic Retinopathy Study (ETDRS) grid sectors segmented into eight layers including the macular retinal nerve fiber layer (mRNFL), ganglion cell layer (GCL) and inner plexiform layer (IPL) using Heidelberg Spectralis. This single-center clinic-based case-control study performed in Spain included one eye of 56 normal healthy participants, 63 ocular hypertensives (OHT), 32 early primary open angle glaucoma (POAG) (MD > -6) and 42 moderate to advanced POAG (MD ≤ -6). The reference standard for POAG was determined using both structural (optic nerve head cupping or damage) and functional (standard automated perimetry) parameters. OHT was defined as intraocular pressure (IOP) > 21 mmHg with normal optic disc and perimetry. SD-OCT was performed on all participants by one experienced operator.

Values for mRNFL, GCL and IPL showed significant differences between the four groups (Kruskal- Wallis test) therefore their potential to discriminate between early glaucoma and OHT was studied further. The greatest areas under the curve (AUCs) to detect early POAG from OHT were reported for outer inferior sector mRNFL (0.781) and for outer temporal sector GCL (0.760) and outer temporal sector IPL (0.767) and for a combination of all three (0.807) with a best combination of sensitivity and specificity of 0.762 and 0.719 for the combination.

The results [...] are consistent with the macula vulnerability zone (MVZ) theory and demonstrate promise for the use of macular parameters as biomarkers for the early detection of glaucoma

These results are in agreement with a study by Chien et al. who reported the diagnostic performance of segmented EDTRS grid sectors using Heidelberg Spectralis in 87 glaucomatous eyes and 69 normal eyes: outer inferior sector mRNFL (0.930) and outer temporal sector GCL (0.942).² The higher AUCs in this study are likely to be due to the comparison between glaucomatous eyes and normal eyes rather than the comparison between OHT and early glaucoma by Cifuentes- Canorea et al.

The results of both of these studies are consistent with the macula vulnerability zone (MVZ) theory and demonstrate promise for the use of macular parameters as biomarkers for the early detection of glaucoma.³ Meta-analyses of studies and future studies that adopt population-based and clinical pathway designs should provide more data and aim to avoid the pitfalls of diagnostic case-control studies which tend to overestimate diagnostic accuracy. Future studies that compare diagnostic utility of segmented macular scans with cRNFL and Bruch's membrane opening minimum rim width (BMO-MRW) parameters would also be of interest.

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