PURPOSE: To compare macular thickness and best-corre-cted visual acuity (BcVA) before and after panretinal photocoagulation (PRP) in patients with severe diabetic retinopathy and good visual acuity (VA) to identify factors that predict post-operative visual function. DESIGN: Prospective, non-comparative, interventional case series. METHODS: Sixty-four consecutive patients with severe non-proliferative diabetic retinopathy or with non-high-risk proliferative diabetic retinopathy whose VA was 20/20 or better before PRP were studied. Sixty-four eyes of 64 patients underwent scatter PRP in four sessions every other week. Macular thickness was measured by optical coherence tomography (OCT), and VA was measured before and periodically after PRP. RESULTS: During the 24- week observation period, patients were classified into three groups according to changes in VAduring the post-operative period. In groupA, VA was maintained at pre-operative levels in 54 (84% ) eyes during the 24 weeks after PRP. In group B, VA initially decreased in three eyes but subsequently recovered to baseline during the observation period; in group C, VA did not recover during follow-up in seven eyes. There was no significant difference in pre-operative foveal thicknesses among the three groups, but parafoveal thickness was < 260 μ m in group A, ranged from 270 to 280 μ m in group B, and was > 300 μ m in group C. CONCLUSION: For eyes with severe diabetic retinopathy and good VA, PRP did not affect post-operative VA in more than 80% of patients. Patients whose pre-operative parafoveal thickness was > 300 μ m had a worse visual prognosis. PURPOSE: To compare macular thickness and best-corre-cted visual acuity (BcVA) before and after panretinal photocoagulation (PRP) in patients with severe diabetic retinopathy and good visual acuity (VA) to identify factors that predict post-operative visual function. DESIGN : Prospective, non-comparative, interventional case series. METHODS: Sixty-four consecutive patients with severe non-proliferative diabetic retinopathy or with non-high-risk proliferative diabetic retinopathy whose VA was 20/20 or better before PRP were studied. Sixty- Four eyes of 64 patients underwent scatter PRP in four sessions every other week. Macular thickness was measured by optical coherence tomography (OCT), and VA was measured before and periodically after PRP. RESULTS: During the 24-week observation period, patients were classified In group A, VA was maintained at pre-operative levels in 54 (84%) eyes during the 24 weeks after P RP. In group B, VA initially decreased in three eyes and yet recovered to baseline in the observation period; in group C, VA did not recover during follow-up in seven eyes. There was no significant difference in pre-operative foveal thicknesses among the three groups, but with parafoveal thickness was <260 μm in group A, ranged from 270 to 280 μm in group B, and was> 300 μm in group C. CONCLUSION: For eyes with severe diabetic retinopathy and good VA, PRP did not affect post-operative VA in more than 80% of patients. Patients whose pre-operative parafoveal thickness was> 300 μ m had a worse visual prognosis.