Retinal thickness analysis with time and spectral-domain optical coherence tomography. Cross-platform interchangeability of manual measurements

{BACKGROUND} {AND} {AIM} {OF} {THE} {WORK:} retinal thickness values obtained by automated analysis with new spectral-domain optical coherence tomography ({OCT)} devices exceed those measured by old time-domain {OCTs.} Aim of the present work is to assess reproducibility and comparability of manual measurements performed on both time-domain and spectral-domain {OCT} scans. {METHODS:} 6 eyes were scanned using Stratus {OCT3} and Cirrus hd-{OCT.} Raw exported images were analyzed by ordinary computer software; multiple manual measurements of retinal thickness were taken at different eccentricities. Stratus Retinal Thickness ({SRT)} was measured from Internal Limiting Membrane ({ILM)} to the photoreceptors Internal-Outer Segment interface ({IS/OS)}, while two series of measurements were performed in Cirrus images: {CRT} = Cirrus-{RT} (from {ILM} to the Retinal Pigment Epitelium, {RPE)} and {cCRT} = corrected-{CRT} (from {ILM} to {IS/OS).} Measurements were repeated twice in two eyes and reproducibility was assessed by Intra-Class correlation ({ICC)} and Coefficient of Variation ({CV).} Bland-Altman plots, paired t-test and {ICC} were used for comparative analysis between Stratus and Cirrus measurements. {RESULTS:} Mean {SRT}, {CRT} and {cCRT} values +/- {SD} were respectively 244.75 +/- 34.78 microm, 275.78 +/- 34.36 microm and 244.95 +/- 33.78 microm. Paired t-test resulted in p{\textless}0.0001 comparing {SRT} and {CRT} series, versus p=0.6544 between {SRT} and {cCRT} series. {ICC} was 0.65 between {SRT} and {CRT} and 0,94 between {SRT-cCRT.} Reproducibility of the measurements was excellent ({CV=2},13\% for Stratus and 1,62\% for Cirrus; {ICC=0},994 for both devices). {DISCUSSION:} while a systematic error affects comparison of Stratus and Cirrus macular thickness maps, manual linear measurements result interchangeable, hence allowing comparison of images acquired with either {OCT} systems. (www.actabiomedica.it).