Effect of Inconsistent Optical Coherence Tomography Scan Location on Glaucoma Progression Analysis

Precis: Circumpapillary retinal nerve fiber layer (RNFL) thickness change induced by optical coherence tomography (OCT) scan circle location displacement was not completely compensated despite the use of Guided Progression Analysis (GPA), especially when the "R1" registration method was applied. Purpose: The purpose of this study was to evaluate the effect of inconsistent OCT scan location on glaucoma progression detection using GPA. Methods: Eighty-four glaucomatous eyes with at least 4 serial OCT tests were included. To evaluate the ability of OCT GPA to adjust the OCT scan location, an analysis was performed without manipulation (control set), and after the OCT scan of the latest test was intentionally moved inferotemporally (test set). The eyes were classified into the adjustment and nonadjustment groups based on the superior or inferior quadrant RNFL thickness agreement between the control and test sets. Results: When the OCT GPA parameters between the control and test sets were compared, the test set showed a greater superior RNFL thickness and lesser inferior RNFL thickness compared with the control set (P<0.05). The eyes in the nonadjustment group (n=21, 25%) had a lower chance of applying the eye-tracking function (P=0.003) and a higher frequency of the "R1" registration method of OCT GPA (P<0.001) than the adjustment group (n=63, 75%); all eyes with the "R1" method were in the nonadjustment group and all eyes with the "R2" method were in the adjustment group. Conclusions: Inconsistent OCT scan location induced changes in RNFL thickness that were not completely compensated despite the use of OCT GPA, especially when the "R1" registration method was applied. These findings indicates a potential for misidentified glaucoma progression.