INTRODUCTION: Cases series and randomized studies support the use of isovolumic hemodilution at the acute phase of the central retinal vein occlusion (CRVO). However, a recent meta-analysis showed the difficulty of interpreting the long-term effect of isovolumic hemodilution because of the late complications and the concomitant use of other treatments. We present here a pilot case-series study aiming to demonstrate the effect of isovolumic hemodilution at the acute phase of the disease, before any other treatment was applied. PATIENTS AND METHOD: Twenty-two consecutive cases of CRVO were prospectively treated with isovolumic hemodilution within 15 days of disease onset (substitution of 10 ml/kg of blood by a macromolecular solution (Voluven), aiming at a hematocrit of 35%). The treatment was performed in ambulatory conditions after excluding common contraindications (cardiac, respiratory and renal insufficiency, angina pectoris, history of heart attack or stroke during the last 6 months). The patients were followed prospectively with respect to visual acuity, fluorescein angiography and visual acuity at one week, one month, three months and twelve months. RESULTS: Visual acuity improved of at least one ETDRS line (5 letters) in 59% of the patients one week after the treatment. Improvement in the haemodynamic was observed in all these cases on fluorescein angiography. The vision remained stable at 1 month and 3 months before any other treatment was applied. After the 3rd month, additional intravitreous injection of triamcinolone was applied in 32% of eyes for persistent macular edema. At 12 months after hemodilution, visual acuity improved in 64% of cases and only 5% of the eyes converted into an ischemic CRVO. DISCUSSION: Isovolumic hemodilution at the acute phase of the CRVO is followed by an improvement in both vision and angiographic characteristics in more than 60% of our patients and the conversion into an ischemic form was limited to 5% of eyes. Further randomized studies are needed to evaluate the specific effect of hemodilution in the long term.