Scanning Circle Location Affects NFL Assessment on StratusOCT

Abstract

Abstract: : Purpose. To investigate the effect of scanning circle location on nerve fiber layer (NFL) assessment using optical coherence tomography (OCT; Stratus OCT, Carl Zeiss Meditec, Inc., Dublin, CA). Methods: Ten normal volunteers were enrolled in this study. Circumpapillary StratusOCT scans (fast RNFL thickness scan protocol with 3.4mm scanning circle diameter) were performed by placing the scanning circle on 5 different locations; centered on the optic nerve head, 2 clicks on arrow buttons for scanning line movement (approximately 0.2 mm on eyes with an axial length of 24.47mm) up, right, down, and left from the center. NFL analysis data were exported to an IBM compatible PC, and a software program of our own design automatically detected locations of the highest peak in both superior and inferior quadrants on the NFL thickness plot and measured the distance in between the peaks. Results: Superior quadrant mean NFL thickness showed significant differences between the centered circle scans and either upward, downward, or right displaced circle scans (p<0.0001, p=0.006, and p=0.048, paired t–test, respectively), while there were no differences between the centered circle scans and left displaced circle scans (p=0.76). Inferior quadrant mean NFL thickness showed significant differences between center and either upward or downward displacement (both p<0.001), but not between center and either left or right displacement (both p>0.22). Temporal and nasal quadrants showed significant differences between center and either left or right displacement (all p<0.001) but between center and either upward or downward displacement (all p>0.17). Distance between the peaks showed significant differences between center and either left or right displacement (both p<0.0001), but not between center and either upward or downward displacement (both p>0.19). 30.6% of the displaced scans showed abnormalities in at least one clock hour in comparison with the built–in normative database due to shifting of the peak locations, while all centered scans were within normal limits. Conclusions: Scanning circle location affects StratusOCT NFL assessment. One should pay close attention on the circle location when interpreting NFL assessment outputs.

Keywords: imaging/image analysis: clinical • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • nerve fiber layer