PURPOSE: Compare changes in retinal nerve fiber layer (RNFL) thickness between eyes assigned to intravitreous ranibizumab or panretinal photocoagulation and assess correlations between changes in RNFL and visual field sensitivity and central subfield thickness. METHODS: Eyes with proliferative diabetic retinopathy were randomly assigned to ranibizumab or panretinal photocoagulation. Baseline and annual follow-up spectral domain optical coherence tomography RNFL imaging, optical coherence tomography macular imaging, and automated static perimetry (Humphrey visual field 60-4 algorithm) were performed. RESULTS: One hundred forty-six eyes from 120 participants were analyzed. At 2 years, for the ranibizumab (N = 74) and panretinal photocoagulation (N = 66) groups, respectively, mean change in average RNFL thickness was -10.9 ± 11.7 μm and -4.3 ± 11.6 μm (difference, -4.9 μm; 95% confidence interval [-7.2 μm to -2.6 μm]; P < 0.001); the correlation between change in RNFL thickness and 60-4 Humphrey visual field mean deviation was -0.27 (P = 0.07) and +0.33 (P = 0.035); the correlation between change in RNFL thickness and central subfield thickness was +0.63 (P < 0.001) and +0.34 (P = 0.005), respectively. CONCLUSION: At 2 years, eyes treated with ranibizumab had greater RNFL thinning than eyes treated with panretinal photocoagulation. Correlations between changes in RNFL thickness, visual field, and central subfield thickness suggest that the decrease in RNFL thickness with ranibizumab is likely due to decreased edema rather than loss of axons.