Ganglion Cell Layer Thickness Variance Using SPECTRALIS Optical Coherence Tomography

Background: To determine the normal variance of the mean macular ganglion cell layer (GCL) volume among subjects without significant ocular pathology using SPECTRALIS optical coherence tomography (OCT). Methods: Fifty subjects underwent a baseline scan using SPECTRALIS OCT followed by 2 more studies with (reg-ON) and without (reg-OFF) eye registration all taken at the same session. The mean GCL volume was measured using built-in SPECTRALIS software. Eyes with macular pathology were excluded. The reproducibility of the measurements of the GCL volume was evaluated with Bland-Altman plots and limits of agreement, intraclass correlation coefficient (ICC), and the coefficient of repeatability (CR). Results: A total of 98 eyes met criteria for the analysis. The mean GCL volume difference was 0.0002 +/- 0.029 and -0.0005 +/- 0.035 mm(3) for scans 1 versus 2 (baseline vs reg-ON) and 3 (baseline vs reg-OFF), respectively. The ICCs were 0.985 and 0.977 for the baseline vs reg-ON and reg-OFF groups. The CR for baseline vs reg-ON was 0.056 while CR for baseline vs reg-OFF was 0.069. Ninety percent of eyes fell within 0.04 mm(3) of test-retest reliability. Conclusions: Our model found a predictable threshold of 0.07 mm(3) or less for SPECTRALIS OCT mean GCL volume variance, which did not significantly change with eye registration in eyes without macular pathology. Clinicians may also consider a threshold of 0.04 mm(3) when determining stable vs progressive changes in mean GCL volume using this device.