Ophthalmological surgery can be performed under topical, regional or general anesthesia. Recently, the majority of ocular surgeries performed by regional rather than general anesthesia, because of the regional anesthesia is more economic, easy to perform, and the risk involved is less. Orbital regional anesthesia can be done using a retrobulbar (intra-conal) block, peribulbar (extra-conal) block or sub-Tenon's block.~The STBs or episcleral block was first described by Turnbull in 1884 and it was repopularized in the 1990s as a simple and safe alternative to needle-based eye blocks. The STB becomes the most widely practiced regional technique for cataract surgery, because it produces satisfactory anesthesia for most intraocular procedures, and avoids the inherent risks of needle-based blocks, such as globe perforation and optic nerve injury.~Dexmedetomidine is a selective α-2 receptor agonist that produces sedation and analgesia without causing respiratory depression. It also allows patients to respond to verbal commands during the sedation; easy conversion from sleeping to awakening is possible. Therefore, dexmedetomidine has been used as sedative in various clinical fields in intensive care unit and surgery and an adjuvant to local anesthetics.~Many studies were done to evaluate its effect as sedative or anlgesic when administered either intravenously or when added to local anesthesia in ophthalmic block. But no one, till now comparing its effect when used as adjuvant to local anesthetics or administered intravenously in subtenon block.
The study designed to compare the effects and the safety of adding dexmedetomidine to local anesthetics and its intravenous administration in subtenon block in patients undergoing cataract surgery.