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. 2008 Aug;17(5):333-40.
doi: 10.1097/IJG.0b013e3181650f8b.

An analysis of normal variations in retinal nerve fiber layer thickness profiles measured with optical coherence tomography

Quraish Ghadiali  1 , Donald C Hood, Clara Lee, Jack Manns, Alex Llinas, Larissa K Grover, Vivienne C Greenstein, Jeffrey M Liebmann, Jeffrey G Odel, Robert Ritch
Affiliations

An analysis of normal variations in retinal nerve fiber layer thickness profiles measured with optical coherence tomography

Quraish Ghadiali et al. J Glaucoma. 2008 Aug.

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.

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Figures

FIGURE 1
FIGURE 1
A, The RNFL thickness of all 48 individuals’ right eyes as a function of distance (in degrees) around the optic nerve head starting at the temporal most point (9 o’clock of the right eye). The black curve is the average of all 48 individual RNFL profiles. B, As in A for the left eyes.
FIGURE 2
FIGURE 2
A, Amplitude of the peak in the superior portion of the RNFL profile of the right eye versus the amplitude of the superior peak in the left eye. B, Same as in A for the peaks in the inferior portion of the RNFL profiles. C, Location of the peak in the right eye versus the location of the peak in the left eye for both the superior (circles) and inferior (squares) peaks. Filled symbols indicate the peak was not the most temporally located maxima. D, Example of an individual’s RNFL profiles in which the peaks for the right (black) and left (gray) eyes were not the most temporally located maxima.
FIGURE 3
FIGURE 3
A, Individual RNFL profiles (gray), with the average of all profiles (black), for the 5 highest coefficients of determination (R2) values. B and C, Same as in A for the 5 lowest R2 values (B) and the next 5 lowest R2 values (C).
FIGURE 4
FIGURE 4
A, Normalized (scaled) individual RNFL profiles (gray), with the average of all normalized profiles (black), for the 5 lowest R2 (norm) values. B, Same as in A for the next 5 lowest R2 (norm) values.
FIGURE 5
FIGURE 5
Normalized R2 values plotted against interocular R2 values of the (A) right and (B) left eyes.
FIGURE 6
FIGURE 6
The RNFL report for an individual whose left eye was scored as abnormal based on the clock hour analysis. The arrows indicate the location of the abnormal RNFL thickness in the left eye.
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