Abstract

Eye lesions are commonly observed in pinnipeds.^2,3,5 Clinical assessment is challenging because animals are usually blepharospastic due to ocular pain, and under inhalant anesthesia the eye globe rotates ventrally making observation difficult. Retrobulbar and auriculopalpebral nerve block techniques have been developed in other species to alleviate these difficulties and allow better ocular assessment.^1,4,6 Ocular nerve block techniques were developed for California sea lions (Zalophus californianus) using lidocaine 2%. To develop the retrobulbar block derived from methods usually used in domestic animals,^1,4,7 a variety of needle sizes, anatomic approaches, and volumes of methylene blue were injected into the orbits of 10 California sea lion cadavers. An optimal technique, based on distribution of methylene blue dye into periocular muscles and tissues, was determined to be two-point (ventrolateral and ventromedial) transpalpebral injection with a 20G, 1 1/2" needle. This site was then tested using lidocaine on 26 anesthetized animals prior to euthanasia and on one animal treated for ocular disease. A dosage of 4 mg/kg was considered to have good results and minimal complications. The retrobulbar block technique had a 76.9% rate of success (using 4 mg/kg lidocaine), with success defined as the animal's eye globe returning at least half way to its central orientation with mydriasis and mild exophthalmos. No systemic adverse effects were noted using this technique, with stable cardiovascular parameters and no evidence of damage to the globe at necropsy. The auriculopalpebral nerve block was also adapted for California sea lions from the technique described in dogs, cattle, and horses.^4,7 Lidocaine was injected by subcutaneous infiltration lateral to the orbital rim, where the auriculopalpebral branch courses over the zygomatic arch. This block was used in five blepharospastic animals that were anesthetized for an ophthalmic exam. The auriculopalpebral nerve block had a 60% rate of success, with success defined as reduction or elimination of blepharospasm for up to three hours.

Acknowledgements

To all the collaborators of this study, especially all the staff and visitors of The Marine Mammal Center that worked with us in the necropsy room and in clinics. We would also like to acknowledge veterinary ophthalmologists Dr. Patricia Smith, Dr. Carmen Colitz, Dr. Katie Freeman and veterinary radiologist Dr. Sophie Dennison, for their consultation and suggestions.

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