Reproducibility of spectral-domain optical coherence tomography RNFL map for glaucomatous and fellow normal eyes in unilateral glaucoma

Purpose: To compare the reproducibility of the optical coherence tomography (OCT) retinal nerve fiber layer (RNFL) thickness map between glaucomatous and fellow normal eyes of unilateral glaucoma patients. Methods: In this prospective case-control study, Cirrus HD-OCT was performed for 79 unilateral glaucoma patients 3 times on the first visit and on 3 subsequent visits within a 2-month period. Test-retest standard deviation (TRT-SD) and tolerance limit based on the 1.645×√2×TRT-SD formula were derived for RNFL thicknesses at the respective superpixels of the RNFL thickness map. Results: The TRT-SDs and tolerance limits of the glaucomatous eyes (TRT-SD: 2.75 to 20.25 μm; tolerance limits: 6.40 and 47.11 μm) were significantly smaller than those of the fellow normal eyes (TRT-SD: 2.73 to 26.49 μm; tolerance limits: 6.35 and 61.63 μm) in the superotemporal, inferotemporal, and superonasal areas (P <0.05). The TRT-SDs in most areas showed a significant positive correlation with the RNFL thicknesses (P<0.05). Conclusions: The test-retest variabilities of the Cirrus HD-OCT RNFL thickness map of the glaucomatous eyes were lower than those of the fellow normal eyes, especially in areas of high diagnostic importance. Moreover, variability was positively correlated with the baseline RNFL thicknesses. Therefore, adjusting the tolerance limits on the basis of the baseline RNFL thickness values might help improve the ability to recognize progression. Further prospective studies on this issue are warranted.