Clonidine - Ropivacaine in Peribulbar Anesthesia

Inclusion Criteria: * patients who have given written informed consent * any adult patient about to undergo their first operation involving the posterior segment of the eye under peribulbar anaesthesia Exclusion Criteria: * persons without National Health Insurance * pregnant or breast-feeding women, patients \< 18, patients who cannot give their consent, patient's refusal of Loco-Regional Anesthesia, patients who cannot remain in dorsal decubitus dorsal for at least 1h * contra-indication for Loco-Regional Anesthesia * hypersensitivity to the study drugs (ropivacaine, clonidine), to the corresponding excipients or hypersensitivity to local anaesthetics other than amide-type ropivacaine. * disorders of periorbital or oculomotor sensitivity, patients with glaucoma, patients with chronic pain and on morphines * uncontrolled arterial hypertension, clonidine per os at home, arterial hypotension before the intervention (SAP \< 90 mmHg) * Surgery for diabetic retinopathy, patients with unbalanced diabetes, eye with prior posterior segment surgery * Contra-indications mentioned on the summary of product characteristics for clonidine (known hypersensitivity to the active ingredients or one of its excipients, Heart rate below 60bpm, severe Bradycardia due to sinoatrial node disease or second or third degree atrioventricular block, Depression, Sultopride).