If on the test at time 2 (T C2), one of the locations with an open triangle on T C1 ( Fig, 1B) is also significantly less sensitive, again compared to baseline, then a half-filled triangle appears. Note, it takes 3 tests to analyze whether the sensitivity at a given point has decreased, two baseline tests and the test at T C1. In this example, 3 points met this criterion. An open triangle indicates that the sensitivity at that point on the current test (T C1) has decreased at the p<5% level as compared to the average of two baseline tests (first row in Fig. The key aspect of this report is the Progression Analysis, shown within the red rectangle in panel A. Figure 1 provides an example of the GPA Summary Report for the 24–2 test. The GPA is undoubtedly the most sophisticated, and probably the most useful, clinical tool for identifying progression based upon multiple 24–2 visual fields. Thus, the GPA OCT report, like the GPA 24–2 visual field report, is not designed to answer a fundamental clinical question important to both the patient and the clinician, namely: Did damage progress since the last visit? Our purpose here is to first review the OCT GPA and to illustrate how its design limits answering this fundamental question, and second to discuss approaches for answering this question, including the need to evaluate both RNFL and GCL probability maps, and to scrutinize circumpapillary OCT b-scans. In particular, the Zeiss GPA reports for retinal nerve fiber layer (RNFL) and ganglion cell + inner plexiform layer (GCIPL) thicknesses are, like the GPA for 24–2 test, based upon the assumption that one needs a minimum of 4 tests to detect “likely” progression. The same approach has been extended to the analysis of progression using optical coherence tomography (OCT). The GPA has helped overcome the variability in visual field testing, and enabled more objective judgements to be made. 1– 3 The Zeiss’ clinical report, the “Guided Progression Analysis (GPA) for 24–2 Test” (Carl Zeiss Meditec, Inc., Dublin, CA) was based upon this research. Based upon years of research, it is generally accepted that multiple visual field tests are required to reliably, and statistically, establish progression. However, the repeat variability of this test has been a major obstacle to successful detection of progression. Among the tools available to the clinician is the visual field test obtained with static automated perimetry. Identifying progression is of fundamental importance to the management of glaucoma.

In addition, we argue that the clinician can make a better decision about suspected progression between two test days by topographically comparing the changes in the different OCT maps and images, as well as topographically comparing the changes in the visual field to the changes in the OCT probability maps. Instead of relying on the GPA analysis or summary statistics, one needs to evaluate RNFL and GCIPL probability maps and circumpapillary OCT b–scan images. However, these statistics have poor sensitivity and specificity due to segmentation and alignment errors. However, the OCT GPA requires a minimum of 3 tests to determine “possible loss (progression)” and a minimum of 4 tests to determine if the patient shows “likely loss (progression).” Thus, it is not designed to answer a fundamental question asked by both clinician and patient, namely: Did damage progress since the last visit? Some clinicians use changes in summary statistics, such as global/ average circumpapillary RNFL thickness. More recently it has been extended to retinal nerve fiber layer (RNFL) and ganglion cell + inner plexiform layer (GCIPL) thicknesses measured with optical coherence tomography (OCT). The most sophisticated, and probably the most useful, commercially available clinical tool for identifying progression is the Guided Progression Analysis (GPA), which was initially developed to identify progression using 24–2 visual field tests.

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