Department of Animal Sciences, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, Israel.

Rats are commonly used as an animal model to study glaucoma, which is induced experimentally using invasive painful procedures. Peribulbar anesthesia (PBA) is frequently used in people and domestic animals prior to ophthalmic surgeries to provide excellent perioperative analgesia. The goal of this study was to develop a PBA technique adapted to rat anatomy, to improve welfare of animals used as a glaucoma model. Eighteen rat cadavers were used to establish the optimal injection technique and the volume of injectate required. Four injection techniques using lidocaine 2% and contrast agent (1:1 volume ratio) were compared using computed tomography (CT) imaging performed before and after injection. A board-certified radiologist, masked regarding the injection techniques used, reviewed all CT images and scored injectate distribution at 4 locations: extraconal, intraconal, around the optic nerve and at the orbital fissure (scale 0-8; 0=none, 8=excellent). Injectate distribution scoring (median; range) was significantly higher (i.e., better) using the dorso-medial (5; 2-6) and medial-canthus (4.5; 2-8) techniques compared with mid-ventral (3; 2-5) and ventro-lateral (2; 1-3) techniques. A volume of 0.1 mL/100 g body weight provided overall good distribution, while a volume of 0.2 mL/100 g produced excessive exophthalmos. Presence of intracranial contrast was observed following all technique. In conclusion, PBA using the dorso-medial or medial-canthus techniques are most likely to provide local anesthesia. The intracranial contrast observed could be the result of post-mortem vessel leakage. Results of this preliminary study will be used to assess the efficacy and safety of these techniques in experimental rats. [ABSTRACT FROM AUTHOR]