Experiences with the local retrobulbar anesthesia in ophthalmologic surgery of the standing horse

Abstract

Experiences with the local retrobulbar anesthesia in ophthalmologic surgery of the standing horse Local retrobulbar anesthesia of the optic nerve is performed with a hypodermic needle 20 G, 70mm, or with a flexible catheter pushed through a Tuohy epidural needle. The local anesthetic agents cause analgesia extending to the anterior ocular parts, including cornea and conjunctiva. Furthermore, a total akinesia of the globe and a sensory block of the optical nerve are induced, with a reversible loss of vision. Unlike in humans, there are only few blood vessels near the injection site in horses. This was approved by initial examinations with ultrasound (including colour flow Doppler), computed tomography, and anatomical preparation. No serious hemorrhage or other complications hazardous to vision or life could be seen. Ocular surgery in the standing horse with selective nerve blocks is indicated in all horses classified as high-risk patients, especially in geriatric horses. Meanwhile there are several surgical procedures that can be performed with the same accuracy and quality as under general anesthesia, besides the established enucleation. The long-lasting analgesic effect after pre-surgical administration, which is far longer than the pharmacological effect, is an additional benefit of local retrobulbar anesthesia.

Safety and accuracy of blind vs. ultrasound‐guided dorsal retrobulbar nerve blocks in horses—A cadaveric study

“…The previously described “popping” sensation was inconsistently observed ( n = 19/44). This difficulty was not reported in previous clinical 6,25 or cadaver 16 studies in horses. In frozen specimens, the effects of the freeze–thaw process on soft tissues can potentially change their biomechanical characteristics.…”

Local anaesthetic techniques for the equine head, towards guided techniques and new applications

“…Needle placement within the cone formed by the retractor bulbi muscles was found to lead to a more effective spread of the injected fluid towards the orbital fissure and the subjective evaluation of ultrasound performance appeared to correlate well with the results of the CT images. Toth and Hollerrieder () also have described an ultrasound‐guided retrobulbar block in horses with a similar approach ( Fig ), followed by CT assessment of local anaesthetic spread. They describe the use of Tuohy needles to advance a catheter into the retrobulbar intraconal location for repeated injections.…”