Quantifying the Rate of Ellipsoid Zone Loss in Stargardt Disease

Abstract

To determine a reliable method of using the ellipsoid zone (EZ) on optical coherence tomography (OCT) to track disease progression in Stardgardt disease (STGD). Retrospective reliability study. STGD patients with genetically confirmed ABCA4 gene mutations seen at the Wilmer Eye Institute with follow-up visits separated by at least 12months were identified. Spectral-domain optical coherence tomography (SD-OCT) macula volume scans centered at the fovea and fundus autofluorescence (FAF) images were obtained. The area of EZ loss was calculated from the SD-OCT and the area of retinal pigment epithelium (RPE) loss from the FAF. Scans were reanalyzed by the primary grader to assess intragrader reliability, and reanalyzed by a second grader to assess intergrader reliability. Sixteen STGD patients (total of 31 eyes) were followed for a mean of 2 years (range 1-4.7 years). The mean rate of EZ loss, 0.31 ± 0.31mm2/year, was similar to the average rate of RPE loss, 0.33 ± 0.38mm2/year. The average area of EZ loss at the initial examination, 4.18 ± 1.91mm2, was larger than the initial area of RPE loss, 2.25 ± 1.66mm2 (P < .01). The absolute difference of the area of EZ loss on test-retest for the first grader was 0.12 ± 0.10mm2, and between graders 0.21 ± 0.21mm2. The intraclass correlation (ICC) of both intragrader and intergrader reliability for EZ loss was excellent at 0.99. Tracking the area of EZ loss on SD-OCT macular volume scans longitudinally is a reliable way of monitoring disease progression in STGD. This could be used as a sensitive anatomic outcome measure in clinical trials related to STGD.