Misalignments in the Retinal Nerve Fiber Layer Evaluation Using Cirrus High-definition Optical Coherence Tomography

Purpose: To evaluate the frequency and characteristics of misalignments (MAs) in the retinal nerve fiber layer (RNFL) analysis protocol of spectral-domain optical coherence tomography (Cirrus) and determine factors associated with MAs. Methods: Three hundred eyes (162 normal and 138 glaucomatous eyes) were included in this cross-sectional study. The MAs were considered limited when they affected only part of the scan line, and complete (CMA) when they were observed in the entire scan line. A subgroup (153 cases) with repeated scans was analyzed to compare the RNFL thicknesses in the scans with and without CMAs. Results: Two hundred ninety-nine limited MAs were found in 140 eyes (46.7%) and 151 CMAs were found in 91 eyes (30.3%). The frequency and number of CMAs were significantly related to age (P < 0.05). Seventy-two CMAs were in the measurement ring in 48 eyes, more frequently in the 3 and 9-o'clock positions (P = 0.001) and the horizontal quadrants (P = 0.001). Among the repeated scans, the number of cases with CMAs was similar to the first scan (P = 0.32). No significant differences were found in global or quadrant RNFL thickness between scans with and without CMAs. Conclusions: CMAs were present in the first or second scans in about 30% of cases and were related to older age. CMAs were more frequently in horizontal meridians and quadrants. No differences in RNFL thickness were found between scans with and without CMAs in the same patients. Scans with CMAs in the measurement ring can be considered in the RNFL evaluation.