Increasing sampling density improves reproducibility of optical coherence tomography measurements

Purpose: Published series of peripapillary retinal nerve fiber layer (RNFL) measurements using optical coherence tomography (OCT) have sampled 100 eve nly distributed points on a 360 degrees peripapillary circular scan. The go al of this study was to determine whether a four-fold increase in sampling density improves the reproducibility of OCT measurements. Methods: Complete ophthalmic examinations, achromatic automated perimetry, and OCT imaging were performed in all patients. The OCT scanning consisted of three superior and inferior quadrantic scans (100 sampling points/quadra nt) and three circular scans (25 points/quadrant), The RNFL,thickness measu rements and coefficient of variation (CV) were calculated for the superior and inferior quadrants for each sampling density technique. Results: The study included 22 eyes of 22 patients (3 control subjects; 2 p atients with ocular hypertension; and 17 patients with glaucoma). Quadrants with associated glaucomatous visual field loss on automated achromatic per imetry had thinner RNFLs than quadrants without functional defects for both the 25- and 100-points/quadrant scans. For quadrants associated with norma l visual hemifields (n = 22), there was no difference between the 25- and 1 00-points/quadrant scans in mean RNFL thickness and CV. Among quadrants wit h visual field defects (n = 22), RNFL thickness measurements were thinner i n the 25-points/quadrant scans than in the 100-points/quadrant scans. The C V for the 25-points/quadrant scans (25.9%) was significantly higher than th at for the 100-points/quadrant scans (11.9%). Conclusion: Increasing the sampling density of OCT scans provides less vari able representation of RNFL thickness. The optimal sampling density to achi eve maximal reliability of OCT scans remains to be determined.