Effect of motion artifacts and scan circle displacements on cirrus HD-OCT retinal nerve fiber layer thickness measurements

Purpose. To evaluate the effect of scan circle displacements on retinal nerve fiber layer thickness (RNFLT) measurements in Cirrus HD-OCT scans with motion artifacts affecting the optic disc. Methods. In this cross-sectional study, 70 scans from 18 healthy eyes and 100 scans from 26 glaucomatous eyes were divided into 85 pairs, each composed by a scan with one motion artifact affecting the optic disc, and a scan from the same eye without motion artifacts. En face images underwent automated realignment, and horizontal/vertical scan circle displacements were determined. Multiple regression analysis evaluated the relationship between scan circle displacements and RNFLT change. Results. Scans with motion artifacts showed similar displacements in healthy and glaucomatous eyes (P values ≥ 0.08). Average RNFLT and quadrants were relatively unchanged, while clock-hours showed more changes (e.g., in glaucomatous eyes, clock-hour- 7 RNFLT was lower in scans with motion artifacts, P = 0.05). Scan circle displacements produced average RNFLT changes above test-retest variability in 3/85 cases (3.53%). Retinal nerve fiber layer thickness tended to decrease in sectors moved away from the disc and to increase in sectors closer to the disc (R² ≤ 0.40 and R² ≤ 0.22 in healthy and glaucomatous eyes, respectively). In healthy eyes, horizontal displacements ≥ 423 and 325 lm were associated with average and quadrant RNFLT changes above test-retest variability, respectively. Conclusions. Scan circle displacements occurred in all scans with motions artifacts affecting the optic disc. Average RNFLT and quadrants were more robust than clock-hours. Because motion artifacts may be difficult to detect, clinicians should carefully inspect en face OCT images for their presence and interpret clock-hour results cautiously.