This is a study conducted in 60 patients, randomly assigned to one of two groups of 30: the first will receive ropivacaine alone and the second will receive the association ropivacaine/clonidine.

The aim of the study is to prove that the association of Clonidine with Ropivacaine is more effective than ropivacaine alone for locoregional anaesthesia of the eye for retinal surgery.

The principal interest of this association of drugs is that it procures faster and longer anaesthesia of the eye with less ropivacaine (therefore fewer injections). This provides greater comfort to the patient during and after the intervention.

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).