Background Patients with initially low visual acuity were excluded from the therapy approval studies for retinal vein occlusion. But up to 28 % of patients presenting with central retinal vein occlusion have a baseline BCVA of less than 34 ETDRS letters (0.1). The purpose of our study was to assess visual acuity and central retinal thickness in patients suffering from central retinal vein occlusion and low visual acuity (<0.1) in comparison to patients with visual acuity (≥0.1) treated with Dexamethasone implant 0.7 mg for macular edema. Methods Retrospective, controlled observational case study of 30 eyes with macular edema secondary to central retinal vein occlusion, which were treated with a dexamethasone implantation. Visual acuity, central retinal thickness and intraocular pressure were measured monthly. Analyses were performed separately for eyes with visual acuity <0.1 and ≥0.1. Results Two months post intervention, visual acuity improved only marginally from 0.05 to 0.07 (1 month; p = 0,065) and to 0.08 (2 months; p = 0,2) in patients with low visual acuity as compared to patients with visual acuity ≥0.1 with an improvement from 0.33 to 0.47 (1 month; p = 0,005) and to 0.49 (2 months; p = 0,003). The central retinal thickness, however, was reduced in both groups, falling from 694 to 344 μm (1 month; p = 0.003,) to 361 μm (2 months; p = 0,002) and to 415 μm (3 months; p = 0,004) in the low visual acuity group and from 634 to 315 μm (1 month; p < 0,001) and to 343 μm (2 months; p = 0,001) in the visual acuity group ≥0.1. Absence of visual acuity improvement was related to macular ischemia. Conclusions In patients with central retinal vein occlusion and initially low visual acuity, a dexamethasone implantation can lead to an important reduction of central retinal thickness but may be of limited use to increase visual acuity.