Repeatability and Reproducibility of Macular Thickness Measurements Using Fourier Domain Optical Coherence Tomography

Aim: To evaluate repeatability and reproducibility of macular thickness measurements in visually normal eyes using the Topcon 3D OCT-1000. Methods: Phase 1 investigated scan repeatability, the effect of age and pupil dilation. Two groups (6 younger and 6 older participants) had one eye scanned 5 times pre and post-dilation by 1 operator. Phase 2 investigated between-operator, within and between-visit reproducibility. 10 participants had 1 un-dilated eye scanned 3 times on 2 separate visits by 2 operators. Results: Phase 1: No significant difference existed between repeat scans (p=0.75) and no significant difference was found pre- and post-dilation (p=0.54). In the younger group variation was low (95% limits +/- 3.62 mu m) and comparable across all retinal regions. The older group demonstrated greater variation (95% limits +/- 7.6 mu m). Phase 2: For a given retinal location, 95% confidence limits for within-operator, within-visit reproducibility was 5.16 mu m. This value increased to 5.56 mu m for the same operator over two visits and to 6.18 mu m for two operators over two visits. Conclusion: A high level repeatability, close to 6 mu m, of macular thickness measurement is possible using the 3D OCT-1000. Measured differences in macular thickness between successive visits that exceed 6 mu m in pre-presbyopic individuals are therefore likely to reflect actual structural change. OCT measures are more variable in older individuals and it is advisable to take a series of scans so that outliers can be more easily identified.