Nerve Fiber Layer (NFL) Thickness Measurement with Tracking OCT

Abstract

Abstract: : Purpose: To assess the effect of tracking OCT on NFL imaging and reproducibility of NFL thickness measurements. Methods: Peripapillary circular OCT (OCT 2000, Carl Zeiss Meditec, Inc., Dublin, CA) scans were performed on normal, ocular hypertensive, and glaucomatous eyes 20 times with and 20 times without retinal tracking for 3 sessions on 3 different days. Composite images were created from each set of 3 images by aligning each image to its internal limiting membrane. A histogram of each A–scan line was normalized to an arbitrary standard for composite image creation to compensate variable pixel reflectivity level. Composite image creation and NFL thickness measurements were performed using software programs of our own design. Results: Seven normal (mean age 38.4 ± 8.2 years), 5 ocular hypertensive (mean age 64.0 ± 15.1 years) and 4 early glaucomatous eyes (mean age 71.8 ± 9.9 years) were enrolled. Composite tracking images showed sharper edges in the layered retinal structures and better preserved vessel images than without tracking. Mean retinal pixel standard deviation was significantly smaller with tracking than without (490.9 ± 19.3 vs 506.4 ± 31.8, p=0.005, paired t–Test). 2028 out of 2040 images (99.4%) were analyzed successfully for NFL thickness. There was no difference in NFL thickness measurement reproducibility with or without tracking in normal, ocular hypertensive, or glaucomatous eyes (overall coefficient of variation, 4.7 ± 2.5% vs 4.3 ± 3.0%, p=0.45 (normal), 7.3 ± 2.8% vs 9.5 ± 7.2%, p=0.19 (ocular hypertension), 11.3 ± 7.7% vs 8.1 ± 5.3%, p=0.054 (glaucoma)). Conclusions: OCT with retinal tracking improved scan registration variability. We found no effect of tracking OCT on NFL thickness measurement reproducibility.

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