Retinal nerve fiber layer distrubution as measured by optical coherence tomography

Purpose. To measure the distribution pattern of the retinal nerve fiber layer (RNFL) by optical coherence tomography. Methods. Circular peripapillary OCT scans were performed in one eye of 10 normal human subjects. The scan patterns were 2.93, 3.37, and 4.5 mm in diameter and centered on the optic nerve head. RNFL thickness was computed using a pixel-counting algorithm. Results. The overall average RNFL thickness was 150±2.8(s.e.), 137±2.2, and 117±2.2 μm at 2.93, 3.37, and 4.5 mm diameters. The average standard deviation of repeat measurements at the 3 diameters were 4.8, 2.8, and 3.9 μm. The RNFL thickness (μm) fits well (R=0.999) to 54.9 + 138.6 / r, where r is the scan radius (mm). At 2.93 mm diameter, the RNFL was thickest at the superior and inferior clockhours. At 4.5 mm diameter, the thickest portions were shifted one clockhour temporally. Conclusion. OCT provides highly reproducible measurements of RNFL thickness that correlates well with known distribution patterns. RNFL thickness theoretically have a I/R dependence. Curve fit of the data suggests that the pixel-counting algorithm measures predominantly the RNFL, but also include in the estimate a constant 55 μm portion likely from non-RNFL retinal layers.