Prevention of Retinal Non-perfusion in Central Retinal Vein Occlusion by Hydroxycarbamide Treatment.

Inclusion Criteria: * Patients of both sexes of at least 45 years of age. * with social protection * Presenting CRVO for less than 1 month duration * With a decrease of visual acuity and with the best corrected visual acuity lower than 6/10 (73 ETDRS letters) * Signature of informed consent Exclusion Criteria: * predictable lack of compliance to the protocol * monophtalmic patient or any ocular history or condition that could interfere with the study course or results interpretation. * active systemic disease * sickle cell disease * myeloproliferative disease * myelosuppression * kidney or liver insufficiency * ongoing treatment with hydroxycarbamide or anticoagulant * Pregnancy, breast-feeding, no efficient contraception (for both sexes) * wish of paternity (for males of al least 45 years of age)