To compare the changes in macular volume after photocoagulation between eyes with diabetic macular edema with and without visual improvement.Non-experimental, retrospective, longitudinal, comparative study in eyes with diabetic macular edema; the sample was divided in groups: eyes with visual improvement three weeks after photocoagulation (group 1) and eyes without it (group 2). The means of macular volume changes (potential, absolute and percentage) were compared between groups (Student's t test).115 eyes, 50 from group 1 and 65 from group 2; mean macular volume before and after photocoagulation and mean potential, absolute, and percentage volume changes did not differ between groups. 13.9% of the sample had visual improvement and a significant volume reduction; the proportion of the latter did not differ between groups (p = 0.3). Macular volume and visual acuity decreased significantly in eyes without previous visual deficiency (p = 0.012); it was more common to find eyes without visual improvement with a non-significant volume reduction, than finding eyes with visual improvement and a significant macular volume reduction.The reduction of macular volume was not enough to explain visual improvement. Optimizing the outcome in patients with diabetic macular edema requires the identification of functional features with a prognostic value.