Changes in peripapillary retinal nerve fiber layer distribution by axial length.

PURPOSE: To investigate the effect of axial length on the peripapillary retinal nerve fiber layer (RNFL) distribution and the risk of misdiagnosing normal subjects when using the instrument's built-in normative database.
METHODS: Healthy young volunteers underwent ophthalmologic examinations including RNFL thickness analysis with spectral-domain optical coherence tomography (OCT), autorefraction, and axial length measurement. The average RNFL thickness values reported along the calculation circle for whole circle, quadrants, and clock hours were recorded and evaluated at the 5% probability level for significant disparities in comparison with the built-in RNFL database. Angular locations with maximal RNFL thickness in the superotemporal and inferotemporal RNFL humps were determined. The relationships of axial length with these variables were analyzed using both linear regression and logistic regression models.
RESULTS: A total of 485 eyes of 485 subjects were analyzed. The average 360° RNFL thickness became thinner as the axial length increased (r = -0.244, p < 0.001). As the axial length increased, the average RNFL thicknesses in the 1, 2, 4, 5, 6, and 12-o'clock hour sectors decreased whereas those of the 7, 8, 9, 10, and 11-o'clock hour sectors increased. In addition, as the axial length increased, two major RNFL humps were located more temporally and it became significantly more likely for the 1, 2, 5, 6, and 12-o'clock hour sectors to fall below the p < 0.05 significance limits for normal thickness.
CONCLUSIONS: Peripapillary RNFL thickness changes differently in different peripapillary locations as axial length increases. Because long eyes may lead to misleading findings of OCT parameters depending on the peripapillary location, their relationship to the axial length should be considered in the built-in RNFL thickness normative database of OCT.