Guided progression analysis (GPA) is used to help the clinician distinguish between true change and random variability in perimetric results; it uses statistical criteria to determine the significance of any observed changes. Donald Hood, MD, of Columbia University, presented his colleagues’ findings at the 2021 ARVO virtual meeting earlier this week. They found that, due to its performance, 24-2 GPA likely presents a testing burden on patients that can be reduced with OCT.

The prospective study included 99 eyes of 99 patients (29 healthy controls, 70 suspects or eyes with glaucoma) with a baseline 24-2 mean deviation better than -6dB and baseline BCVA better than 20/40. All patients underwent testing at least 12 months after the first of two baseline tests (within about 5.6 days of each other).

OCT testing was a circle scan of the disc and a cube scan that included the macula. The GPA software classified eyes as “likely progressing” (LP), “probably progressing” (PP) or “neither LP or PP.” Three authors rated the likelihood of progression from 0% to 100% (0% to 5% definitely not progressing, 95% to 100% definitely progressing) using a custom-made OCT progression (OCT-P) report.

The researchers reported that the 24-2 GPA identified 13 eyes of either LP or PP. Post-hoc analysis also classified 13 eyes as progressing, but 46% (six eyes) were missed by the 24-2 GPA. “All six GPA misses showed clear progression of glaucoma as indicated by the plots/maps,” Dr. Hood wrote in his ARVO abstract. “Further, six of the eyes identified by the GPA as PP or LP were rated as OCT-not progressing or OCT-neither. These six eyes were likely false positives, as two were healthy controls. The post-hoc analysis couldn’t confirm progression in any of these six eyes, but reasons for a false positive were identified on most (e.g., variable VFs, rim artifacts and/or high local sensitivity at baseline).”

“We could not find detectable OCT changes in at least nine of 10 eyes,” Dr. Hood said in his presentation, in response to whether or not RNFL thinning on B-scan imaging was consistent with 24-2 GPA results. “This doesn’t mean there isn’t some subtle defect going on that we’re missing, of course—we might be missing something—but if any of these 10 eyes are true positives, the associated damage is very, very subtle.”

“In terms of our first purpose, we can conclude that the 24-2 GPA missed about half the eyes identified as progressing on a single OCT follow-up scan,” he noted. “In terms of the second purpose, with the OCT-P method, eyes were identified as progressors based upon a single follow-up test. So, clinically what we’re recommending is that caution should be exercised if the 24-2 GPA is used for clinical decisions. Given it takes a minimum of four tests to identify ‘possible progression,’ the results suggest that the testing burden on patients can be reduced with OCT.”

Question and Answer Session

Claus von der Burchard, MD, of the Universitatsklinikum Schleswig-Holstein University Eye clinic asked about the extent to which OCT might be sufficient for glaucoma monitoring, or if patients would have to undergo both VF and OCT in all cases.

Dr. Hood responded that more work is needed in this area, but “my prediction is that we can get by with fewer VFs, and the ones we do get can be either a 24-2 or 10-2, depending on the OCT results.”

In response to a comment from Mark Kupersmith, MD, about the need for “better structure-function correlation with regional defects, given these may occur, hopefully before more debilitating central 10º ones,” Dr. Hood agreed and replied that the structure-function correlation is “very good if you compare local regions on OCT and 24-2 and 10-2 deviation maps.”

• Only three eyes were identified as progressing with both methods
  
• 11 eyes were identified as progressing by OCT-P method but not 24-2 GPA
• 10 eyes were identified as progressing by 24-2 GPA but not OCT-P method