Influence of Refractive Error and Axial Length on Retinal Nerve Fiber Layer Thickness Assessed by Optical Coherence Tomography

Purpose: To investigate the influence of refractive status and axial length on Retinal Nerve Fiber Layer (RNFL) thickness as measured by Optical Coherence Tomography (OCT). Methods: This cross-sectional study included 116 eyes from 62 participants. Peripapillary RNFL thickness was assessed using the TOPCON 3D OCT-2000 system. Comparisons of RNFL thickness were performed among hyperopic, emmetropic and myopic eyes and the relationship between axial length and RNFL thickness was analyzed. Results: Compared with emmetropic eyes, the hyperopic group demonstrated no statistically significant increase in average RNFL thickness or in the superior, inferior, nasal and temporal quadrants (p = 0.760, 0.160, 0.139, 0.345 and 0.762, respectively). Similarly, the myopic group showed no significant reduction in average RNFL thickness or in any quadrant compared with the emmetropic group (p = 0.991, 0.746, 0.848, 0.382 and 0.894, respectively). A significant inverse relationship was observed between axial length and RNFL thickness. Increasing axial length was associated with a reduction in average RNFL thickness as well as in the superior, inferior and nasal quadrants (p = 0.0009, p = 0.0003, p = 0.0031 and p = 0.0129, respectively). No significant association was found between axial length and temporal quadrant RNFL thickness (p = 0.8118). Conclusion: Refractive status alone, whether myopic or hyperopic, did not significantly influence RNFL thickness measurements. In contrast, increased axial length was associated with significant thinning of the RNFL in the average, superior, inferior and nasal quadrants, while the temporal quadrants remained unaffected. These findings highlight the importance of considering axial length when interpreting RNFL measurements obtained by OCT.