AIM: To evaluate the effect of the laser spot diameter on the reproducibility of the visual field analysis in diabetic patients with upper temporal retinal vein occlusion. MATERIAL AND METHODS: Thirty-six eyes of 36 consecutive type-2 diabetes mellitus patients with upper temporal retinal vein occlusion who required sectoral retinal photocoagulation (SRP) treatment were enrolled for the study. Patients with a history of previous retinal laser photocoagulation, significant lenticular opacities and those whose perimetric test reliability criteria were low (fixation loss >20% and false-positive or false-negative responses >33%) were excluded from the study. SRP was applied to the upper temporal retinal quadrant. Nineteen eyes received SRP treatment with 500-mum laser spots (group 1) while the rest of the eyes (n = 17) received SRP with 300-microm laser spots (group 2). Patients underwent five consecutive visual field analyses, each on a different day during a 2-week period, both before and 6 weeks after SRP. The Humphrey field analyzer central 30-2 threshold test using SITA Standard strategy was applied for visual field testing. RESULTS: The mean age of the patients in groups 1 and 2 were 58.6 +/- 6.7 and 59.1 +/- 7.1 years, respectively (p > 0.05). Pre-SRP mean retinal sensitivities of the lower nasal quadrant in groups 1 and 2 were not different statistically (p > 0.05). Post-SRP mean retinal sensitivity of the lower nasal quadrant was significantly higher in group 2 than group 1. Moreover, mean defect has been found to be lower in group 2 (p < 0.05). The coefficient of variation for pre-SRP retinal sensitivity measurements were 7.9 and 7.6% for groups 1 and 2, respectively (p > 0.05). The coefficient of variation for post-SRP retinal sensitivity measurements were 3.8 and 2.1% for groups 1 and 2, respectively (p < 0.05). CONCLUSION: SRP treatment with 300-microm diameter laser spots may yield more reproducible visual field data than that with 500-mum diameter laser spots. Moreover, the improvement in the retinal sensitivity of the patients with branch retinal vein occlusion is more marked in case where 300-microm laser spots are used. Copyright 2008 S. Karger AG, Basel.