Effect of signal strength on reproducibility of peripapillary retinal nerve fiber layer thickness measurement and its classification by time-domain optical coherence tomography

Purpose: To assess the effect of signal strength (SS) on reproducibility of peripapillary retinal nerve fiber layer (RNFL) thickness measurement (measurement agreement) and its color-coded classification (classification agreement) by time-domain optical coherence tomography (OCT). Methods: Two consecutive Stratus OCT scans with the Fast RNFL protocol were performed in 658 participants. Intraclass correlations and the linear-weighted kappa coefficient were calculated as indicators of RNFL measurement and classification agreement in participants grouped according to the difference in SS between consecutive OCT scans (interscan SS difference). Results: Groups with a larger interscan SS difference (= 2) had lower measurement agreement than those with a smaller interscan SS difference (0 or 1) for the temporal quadrant and total average RNFL. Classification agreement for the nasal quadrant was lower in the groups with a larger interscan SS difference (= 2) than in those with a smaller interscan SS difference. The tendency of SS to affect classification and measurement agreement remained similar in the group with thinner RNFL thickness (≤85 μm), but not in the group with thicker RNFL. Conclusions: Careful attention should be paid when comparing two or more OCT scans for RNFL thickness measurement or its color-coded classification as the agreement may be sensitive to SS differences.