Purpose: Evaluation of the impact of the injection frequency of ranibizumab on best-corrected visual acuity (BCVA) outcomes in patients with diabetic macular edema (DME). Methods: A meta-analysis of randomized controlled trials (RCTs) and real-world studies was performed to quantify the effect of ranibizumab treatment on BCVA and central foveal thickness (CFT) in DME as well as the relationship between the number of injections and the change in BCVA/CFT. Results: All combined sources (29 RCTs and 11 real-life studies) showed a significant increase in BCVA from baseline following anti-vascular endothelial growth factor (VEGF) treatment (8.2, 9.4, and 10.3 ETDRS letters gained after 12, 24, and 36 months of ranibizumab treatment, respectively). The largest changes in BCVA were observed in RCTs and the smallest in real-life studies at 12 months. A significant relationship was found between the number of injections and change in BCVA at 12 months. Conclusions: Inferior vision outcomes were observed in clinical practice compared with RCTs and might be partly attributable to administration of fewer anti-VEGF injections. Physicians should be aware that early and appropriate anti-VEGF treatment regimens are necessary to obtain the results reported in RCTs and help prevent irreversible vision loss in DME patients.