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A. Bruce, I. E. Pacey, P. Dharni, A. J. Scally, B. T. Barrett; Repeatability of Macular Thickness Measurements Using Fourier Domain OCT. Invest. Ophthalmol. Vis. Sci. 2008;49(13):4264.
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© ARVO (1962-2015); The Authors (2016-present)
To evaluate the repeatability of macular thickness measurements in visually normal eyes using the Topcon 3D OCT-1000.
Phase 1 investigated the effect of age, pupil dilation and number of scans on repeatability. Twelve healthy volunteers formed two groups; 6 younger participants (mean 35yrs, range 30-43) and 6 older participants (mean 69yrs, range 57-78). One randomly selected eye was scanned 5 times pre-dilation and 5 times post- dilation with 1% Tropicamide by 1 operator.Phase 2 investigated inter-operator and inter-visit repeatability. One randomly selected eye was scanned in 10 healthy participants (mean 32yrs, range 25 - 44) on 2 separate visits, 1 - 10 days apart (mean 3 days). At each visit 3 scans were carried out by 2 different operators. All scans in phase 2 were recorded through an undilated pupil.In both phases the retinal thickness of each scan was analysed using the Early Treatment of Diabetic Retinopathy Study (ETDRS) 9 region map where region 1 is centred on the fovea. A 3D scan 6 x 6 mm with a density resolution of 256 x 256 was used.
Results were analysed using a repeated measures regression model with random intercept (STATA 9.2)Phase 1: No significant difference existed between each repeat scan (p=0.75) and no significant difference in the scan measurement was found pre- and post-dilation (p=0.54). In the younger group 95% of measurements were within 3.78µm (2 SDs) and the variation was comparable across all 9 ETDRS regions. The older group showed greater variation (95% limits ± 7.6µm).Phase 2: The mean difference between operators was small (0.8µm) but statistically significant (p=0.00). 95% confidence limits were larger for inter-visit repeatability than for intra-visit repeatability (5.4µm vs 2.8µm).
A high level of repeatability of macular thickness measurement is possible using the 3D OCT-1000. Our results indicate that the instrument has a precision close to the manufacturer’s claim of 6µm. Measured differences in macular thickness that exceed 6µm are therefore likely to reflect actual structural change.
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