An Analysis of Normal Variations in Retinal Nerve Fiber Layer Thickness Profiles Measured With Optical Coherence Tomography

Abstract

Purpose To assess the normal variations in retinal nerve fiber layer (RNFL) thickness measured with optical coherence tomography (OCT). Subjects and Methods Both eyes of 48 individuals (age 56.4±9.5 y) with normal vision and refractive errors between ±6.0 D were tested with the fast RNFL scan protocol of the OCT3 (Zeiss Meditech). Their 256-point RNFL profiles were exported for analysis. The location and peak amplitude of the maxima of the RNFL profiles were measured. Intersubject and interocular variations were assessed with a coefficient of determination, R². An R² of 1.0 indicated that the average profile from all 48 individuals (or of the 2 eyes) accounted for 100% of the variation of an individual eye's profile. Results The R² for the interocular comparison was good, with averages of 0.91±0.07 (right eye) and 0.92±0.05 (left eye). The R² for the comparison of the individual's profile to the mean group profile was only 0.61±0.29 (right eye) and 0.65±0.24 (left eye), with 27% of the R² values below 0.5. Even after normalizing each individual's profile by its mean, R² was only 0.75±0.16 (0.75±0.16) for the right (left) eye. The location of the peaks for the right (left) eye ranged over 91 degrees (88 degrees) for the superior peak and over 64 degrees (66 degrees) for the inferior peak. The range of peak amplitudes for the right (left) eye spanned a factor of 1.7 (1.8) and 2.0 (1.7) for the superior and inferior peaks, respectively. Conclusions There was a wide variation in the amplitude and shape of the individual RNFL profiles. However, the RNFL profiles of the 2 eyes of an individual were extremely similar. Adding an interocular comparison with OCT RNFL tests should help identify some false positives.