Intersession repeatability of optical coherence tomography measures of retinal thickness in early age-related macular degeneration

Purpose: To determine the intersession repeatability of Stratus optical coherence tomography (OCT) measures of retinal thickness in patients with age-related macular degeneration (AMD).

Methods: Measurement of retinal thickness was performed over four sessions over 12 weeks using a standardized OCT protocol with the fast macular thickness map in 67 non-treated eyes of 67 patients with AMD enrolled in a clinical trial. The intrapatient standard deviation (S(w) ) and 95% coefficient of repeatability (CR) (1.96×√2×S(w)), expressed in μm and as a percentage of mean retinal thickness, were calculated to estimate intersession repeatability.

Results: The CR was 32 μm for the average retinal thickness in the central 1 mm A1 subfield [95% confidence interval (CI) 31-33 μm] and 53 μm (95% CI 51-55 μm) for the centre-point thickness (CPT). When expressed as a percentage, the CR was 15% (95% CI 14-16) for the central 1 mm A1 subfield and 29% (95% CI 27-30) for the CPT measure.

Conclusion: The average central 1 mm (A1) subfield retinal thickness measure shows good intersession repeatability in patients with stable, early AMD with poorer repeatability for the CPT measure. The results suggest that a change in Stratus OCT retinal thickness of more than 32 μm in the central A1 subfield is more indicative of true clinical change in these patients.