Subclinical Structural and Functional Retinal Alterations in Clinically Normal Myopic Eyes

Background/Objectives: To evaluate subclinical structural and functional retinal alterations in clinically normal myopic eyes using optical coherence tomography (OCT) and automated visual field analysis. Methods: This retrospective observational study included 109 patients aged 18–42 years categorized according to spherical refractive component, while spherical equivalent (SE) was calculated to quantify refractive severity. Only the right eye of each participant was analyzed. Patients were categorized into five refractive groups according to spherical refractive component. All participants underwent comprehensive ophthalmologic examination, axial length (AL) measurement, spectral-domain OCT imaging, and standard automated perimetry. Structural parameters included central retinal thickness (CRT) and OCT-derived nerve fiber layer central thickness (OCT-NFCT). Functional assessment included visual field central zone sensitivity (VF-CZ), peripheral zone defect value (VF-PZ), mean deviation/defect value (VF-MD), and square root of loss variance (VF-sLV). Correlation and regression analyses were performed to evaluate relationships among absolute myopia severity, AL, OCT parameters, and visual field indices. Results: Increasing myopia was associated with significant reductions in CRT (p < 0.001) and significant intergroup differences in OCT-NFCT (p = 0.012). A moderate negative correlation was observed between absolute spherical equivalent/myopia severity and CRT (r = −0.5398, p < 0.001), whereas the association with OCT-NFCT was not statistically significant (p = 0.149). Visual field parameters demonstrated significant deterioration with increasing myopia (all p < 0.001). VF-CZ showed a strong negative correlation with myopia severity (r = −0.8545, p < 0.001), whereas VF-PZ (r = 0.8196, p < 0.001), VF-MD (r = 0.8186, p < 0.001), and VF-sLV (r = 0.7606, p < 0.001) demonstrated strong positive correlations. In multivariable regression analysis, BCVA, AL, and absolute SE were independently associated with VF-CZ, whereas age and absolute SE were independently associated with VF-MD. CRT and OCT-NFCT were not independent predictors of visual field outcomes. Conclusions: Clinically normal myopic eyes demonstrate significant subclinical structural and functional retinal alterations. In this cross-sectional dataset, visual field alterations were detectable across refractive categories and appeared to be more strongly associated with axial elongation and myopia severity than isolated retinal thickness alterations. Combined OCT and visual field assessment may be valuable for early detection and monitoring of subclinical retinal involvement in myopic patients.