Inter-Session Repeatability of Retinal Layer Thickness in Optical Coherence Tomography

Reliable retinal layer thickness measurements using optical coherence tomography (OCT) are important to track the subtle retinal changes in longitudinal studies. A total of 10 eyes (5 healthy subjects, 40 +/- 13 years old) were enrolled to study the inter-session repeatability and identify the pitfalls affecting the reliabilities. Each eye was scanned using spectral domain OCT (Spectralis SDOCT, Heidelberg Engineering) for 3 sessions with 30 seconds rest in between. The first and second sessions were scanned independently and the third one was scanned with the first one as the baseline visit. Each session consisted of a confocal scanning laser ophthalmoscopy (cSLO) image and 61 B-scans of 496x768 pixels. The first, second and third sessions were named as baseline, unregistered and registered sessions; respectively. Seven retinal layers labeled as RNFL, GCL+IPL, INL, OPL, ONL, IS and OS were segmented using a custom software (OCTRIMA3D) and measured in the ETDRS grid. Inter-session standard deviation (sigma), coefficient of repeatability (CR) and coefficient of variations (COV) were calculated to quantify the repeatability. Paired t-test of COVs was used to compare the repeatability and the level of significance was set at 5%. We obtained that values of the CR > 5 mu m and COV of 5%, were revealed only in the outer layers. The values of COV were not significantly different (p< 0.05) in the unregistered scanning session. Our results show that the rotations in the unregistered scanning sessions do not cause significant change in repeatability.