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

Purpose 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. Methods 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. Results 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). Conclusions 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.