Interocular retinal nerve fiber layer thickness symmetry value in normal young adults.

PURPOSE: The aim of this study was to determine the normal range of interocular peripapillary retinal nerve fiber layer (RNFL) thickness symmetry value in young adults. Factors affecting interocular RNFL thickness symmetry were also investigated.
MATERIALS AND METHODS: Both eyes of 241 ophthalmologically and neurologically normal subjects were scanned using optical coherence tomography (200×200 optic disc cube protocol). The effect of ocular cyclotorsion on interocular RNFL thickness symmetry was determined and mathematically accounted for. Symmetry value between the right and left RNFL thickness values was calculated. Linear regression analyses were used to identify correlations between the corrected interocular symmetry value and interocular differences in refractive error, axial length, superior and inferior temporal retinal artery and vein location, and optical coherence tomography signal strength.
RESULTS: The mean interocular RNFL thickness symmetry value before and after correction of ocular cyclotorsion was 0.8791±0.0665 and 0.9044±0.0571 (P<0.001), respectively. Interocular differences in axial length, inferior temporal retinal arcade location, and refractive error were weakly and negatively correlated with the ocular cyclotorsion-corrected symmetry value (P<0.05). Anatomic differences between the eyes in the location of the superior temporal retinal artery and vein were strongly correlated with the corrected symmetry value (P<0.01, R=0.208).
CONCLUSIONS: On the basis of the data obtained here from normal individuals, a corrected symmetry value of <0.77 might indicate the presence of pathologic conditions affecting the RNFL. Interocular RNFL thickness symmetry was influenced more heavily by interocular superotemporal vessel location than by anisometropia.