Scan Tracking Coordinates for Improved Centering of Stratus OCT Scan Pattern

Abstract

Objective 

To describe and evaluate a technique to optimize scan centering during the Stratus optical coherence tomography (OCT) image acquisition process using currently available scan tracking coordinates.

Design 

Observational clinical study.

Participants 

Twelve eyes of six normal subjects were examined using the Fast retinal nerve fiber layer (RNFL) thickness and the Fast Optic Disc acquisition protocols.

Methods 

At visit 1, 3 consecutive measurements (trials) were taken by 2 different operators with the scan subjectively centered on the optic disc for the Fast RNFL thickness protocol and Fast Optic Disc protocol. At visit 2, 3 consecutive measurements were taken by positioning the scan using scan tracking coordinates. The scan coordinates were recorded twice by each operator and the limits of agreement and Bland-Altman plots were used to estimate agreement. The within subjects standard deviation (Sw) and the coefficient of variation (CV) were calculated for RNFL and optic disc parameters for each operator separately and differences by scan positioning method were evaluated using a 3-way (trial x operator x visit) analysis of variance for repeated measures.

Results 

The Sw and CV for the RNFL thickness parameters were generally higher when the scan was subjectively centered on the disc compared to when using the newly described coordinate system (eg, for operator 2, temporal sector Sw was 1.60±0.78 and 4.09±0.99 and CV was 2.2% and 5.7% with and without coordinate use, respectively). For the Fast RNFL protocol, the use of scan tracking coordinates resulted in significantly less variability than subjective placement of the scan circle using the landmark feature (currently recommended technique) in the temporal sectors only. No significant difference was found for any of the optic disc parameters. Bland-Altman plots showed good agreement within each operator for calculating scan coordinates suggesting this technique is reproducible.

Conclusions 

Reproducibility of RNFL thickness measurements generally improves with the use of scan tracking coordinates, particularly in the temporal sector. However, small changes in the position of the scan do not significantly affect the reproducibility of optic disc parameters.