Improved reproducibility of retinal nerve fiber layer thickness measurements with the repeat-scan protocol using the Stratus OCT in normal and glaucomatous eyes

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Abstract
Optical coherence tomography has become within the last years an established imaging technique with many applications in ophthalmology, and an important tool which contributes to earlier and more accurate diagnosis of glaucoma. As a consequence, detection sensitivity is highly valued. The aim of this study was to assess the reproducibility of peripapillary retinal nerve fiber layer (RNFL) thickness measurements by the Stratus Optical Coherence Tomograph (OCT) using the Fast- and Repeat-scan protocols in normal and glaucomatous eyes. In the clinical setting, RNFL thickness measurements were obtained from a control group of 40 subjects, consisting of 20 normal volunteers and 20 glaucoma patients. One eye was randomly chosen from each subject, and underwent five RNFL thickness measurements with the Fast- and five with the Repeat-scan protocol, which was also based on the Fast-scan mode. Reproducibility was assessed by the intraclass correlation coefficient (ICC) and the coefficient of variation (CV) for the overall mean RNFL thickness and for each quadrant and clock hour of the peripapillary area. The Repeat-scan protocol yielded higher ICC and lower CV values in all quadrants and clock hours of the peripapillary area, both in normal and glaucomatous subjects. The difference in CV values between Fast- and Repeat-scan protocol measurements reached statistical significance in the temporal quadrant (P = 0.021) and in clock hour sectors 8, 9 and 12 (P = 0.022, 0.017 and 0.03 respectively). ICC (and CV) for the temporal-, superior-, nasal- and inferior-quadrant RNFL thickness was: for the Fast-scan protocol, 0.913 (7.4%), 0.925 (6.97%), 0.828 (10.31%), 0.964 (4.89%) respectively; and for the Repeat-scan protocol, 0.965 (5.08%), 0.958 (5.26%), 0.906 (8.12%) 0.968 (4.6%) respectively. Reproducibility of RNFL thickness measurements with the Fast- and Repeat-scan protocols by the Stratus OCT is proved to be very high both in normal and glaucomatous subjects. The Repeat-scan protocol shows higher ICC and lower CV values, statistically significant especially on the temporal side of the peripapillary area, which may indicate a higher reproducibility and greater agreement of measurements. These findings support the fact that the Repeat-scan protocol might be considered as a more precise method for evaluation of RNFL thickness.

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