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Editors Selection IGR 7-3

Clinical examination methods: A new ONH volume change-detection method

Comment by Gadi Wollstein & Fabio Lavinsky on:

69386 Structural Change Can Be Detected in Advanced-Glaucoma Eyes, Belghith A; Medeiros FA; Bowd C et al., Investigative Ophthalmology and Visual Science, 2016; 57: OCT511-8

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Detection of glaucoma progression in subjects with advanced glaucoma is challenging because the reliability of visual field (VF) testing is reduced in advanced disease,¹ and OCT circumpapillary retinal nerve fiber layer (RNFL) thickness reaches the minimum practical measurement (floor effect) and further thinning cannot be detected.^2,3 Therefore, studying alternative parameters to detect progression in advanced glaucoma is utterly needed.

The present study investigated if OCT's minimal rim width (MRW) and macular ganglion cell inner plexiform layer (GCIPL) can be useful alternatives to detect progression in eyes with advanced glaucoma (VF MD ≥ 21dB). The OCT scans were analyzed using the author's proprietary segmentation algorithm, and the rate of change was computed for each parameter and compared between advanced glaucoma and control eyes. Additionally, eyes were classified as 'progressing' or 'non-progressing' using a Bayesian kernel detection scheme with ONH analysis and an automated machine classifier method with macular analysis.

Detection of glaucoma progression in subjects with advanced glaucoma is challenging

In advanced glaucoma eyes, the rate of change was non-significant for RNFL and MRW, and significant and steeper than in the control eyes for GCIPL. When eyes were split into progressing and non-progressing groups based on ONH analysis, the rate of change was significantly steeper for GCIPL and not significant for the other structural parameters and VF MD. When progression was defined based on macula analysis, no significant difference was reported for RNFL, MRW and VF MD, but for GCIPL there was a significant thickening reflected in the slope of the progressing group compared with the non-progressing.

These findings demonstrate that GCIPL changed in advanced glaucoma when other structural and VF parameters did not change. However, these results, along with similar longitudinal studies, cannot confirm that these changes truly indicate progression due to the absence of widely accepted gold-standard criteria for progression and the lack of corresponding change with any of the other parameters. Furthermore, the use of customized analysis tools that are not available for clinicians limits the applicability of the findings in clinical practice. Nevertheless, the results provide an important indication that structural changes vary among locations in the eye, and the best method to detect disease progression in the various stages of disease severity should be further investigated.

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