Abstract
ObjectiveTo understand the problems involved in using global OCT measures for detecting progression in early glaucoma.Subjects/MethodsEyes from 76 patients and 28 healthy controls (HC) had a least two OCT scans at least 1 year apart. To determine the 95% confidence intervals (CI), 151 eyes (49 HC and 102 patients) had at least two scans within 6 months. All eyes had 24-2 mean deviation ≥-6dB. The average (global) thicknesses of the circumpapillary retinal nerve fibre layer (cRNFL), GONH, and of the retinal ganglion cell layer plus inner plexiform layer (RGCLP), Gmac, were calculated. Using quantile regression, the 95% CI intervals were determined. Eyes outside the CIs were classified as “progressors.” For a reference standard (RS), four experts evaluated OCT and VF information.ResultsCompared to the RS, 31 of the 76 (40.8%) patient eyes were identified as progressors (RS-P), and 45 patient, and all 28 HC, eyes as nonprogressors (RS-NP). The metrics missed (false negative, FN) 15 (48%) (GONH) and 9 (29%) (Gmac) of the 31 RS-P. Further, GONH and/or Gmac falsely identified (false positive, FP) 10 (22.2%) of 45 patient RS-NP eyes and 7 (25%) of the 28 HC eyes as progressing. Post-hoc analysis identified three reasons (segmentation, centring, and local damage) for these errors.ConclusionsGlobal metrics lead to FPs and FNs because of problems inherent in OCT scanning (segmentation and centring), and to FNs because they can miss local damage. These problems are difficult, if not impossible, to correct, and raise concerns about the advisability of using GONH and Gmac for detecting progression.
Highlights
Detecting the progression of glaucoma is a challenge for the clinician
It is likely that these two measures will miss clear progression of glaucoma, while falsely identifying some eyes as progressors
Eyes whose global cRNFL thickness (GONH) or Gmac metric on the follow-up test were equal or greater than the 95% confidence intervals (CI) were classified as “statistical progressors”
Summary
With the recent incorporation of OCT scanning of the macula, an average (global) measure of the retinal ganglion cell plus inner plexiform layer (RGCLP) thickness has been employed to track progression, and a number of studies have compared these two OCT global measures [1,2,3,4,5,6,7] These two measures, global cRNFL (GONH) and global RGCLP (Gmac), miss early glaucomatous damage clearly visible on probability/deviation maps, which display abnormal regions of RNFL and/or RGCLP thickness [8,9,10]. It is likely that these two measures will miss clear progression of glaucoma, while falsely identifying some eyes as progressors
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