Relationship between supernormal sectors of retinal nerve fibre layer and axial length in normal eyes

To determine the effect of the axial length on the supernormal and false-positive sectors of the peripapillary retinal nerve fibre layer (RNFL) in healthy eyes using the normative database embedded in a spectral domain optical coherence tomographic (SD-OCT) instrument.

This was a prospective, observational cross -sectional study. The right eyes of 126 healthy young volunteers were studied. The RNFL thickness was measured by SD-OCT in twelve 30-degree sectors (clock hours) around the optic disc. The sectors whose RNFL thickness was <5% probability level were labelled as false-positive sectors. The sectors >95% probability level were labelled as supernormal sectors. The relationships between the axial length and rates of supernormal and false-positive sectors were investigated.

A longer axial length was significantly associated with an increase in the rates of supernormal thickness in sector 8 (odds ratio, [OR], 1.494; p = 0.010) and sector 10 (OR, 1.529; p = 0.008). The supernormal sectors were mainly located in the temporal region. A longer axial length was significantly associated with a higher rates of false positives in sector 5 (OR, 1.789; p = 0.017), sector 6 (OR, 2.305; p < 0.001) and sector 12 (OR, 2.277; p = 0.035).

The axial length was significantly related to the rates of supernormal and false-positive sectors even in healthy eyes. These findings indicate that the specificity and sensitivity of SD-OCT will be affected especially in eyes with longer axial lengths.