The patient should be assessed for anaesthesia in the standard manner. Non-consent, inability to comply with the anaesthetist's instructions as, for example, a result of deafness or mental incapacity, inability to lie¯at, allergy to local anaesthetics, lack of i.v. access, or excessive uncontrollable anxiety are absolute contraindications to Sub-Tenon's anaesthesia. The procedure should be explained to the patient to allay anxiety and assist the anaesthetist in carrying out the block.