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 mm³for 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 mm³of test-retest reliability.Conclusions:Our model found a predictable threshold of 0.07 mm³or 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 mm³when determining stable vs progressive changes in mean GCL volume using this device.