Regional Anaesthesia of the Equine Head and Body
Upper eyelid - motor paralysis
This makes examination of the eye much easier Equipment and preparation – Routine skin preparation. 25gauge ⅝ inch needle and 5 ml local anaesthetic. An auriculopalpebral nerve block can be performed at the dorsal edge of the most dorsal point of the zygomatic arch by injecting about 5 ml of local anaesthetic subcutaneously. This block produces no loss of sensation.
This is necessary to remove an eye in a standing horse. They may also be useful when repairing eyelid lacerations.
Equipment and preparation – Because these injections are so close to the eye disinfection of the skin must be done carefully to avoid chemical irritation of the eye. Very dilute povidone iodine solution with no detergent is one option. A 22 gauge 1 inch needle and 3-5 ml local anaesthetic per nerve.
Technique - To completely desensitise the eyelids injections are made at 4 points around the rim of the orbit of the eye in roughly a diamond shape, with the tip dorsally at the supraorbital foramen.
Dorsal – The supraorbital nerve is infiltrated where it exits the supraorbital foramen. Palpate the two edges of the bone bridge caudal to the eye (supraorbital process of the frontal bone) and follow these to the point where they diverge, which is about level with the dorsal rim of the orbit, the foramen will be felt midway between your finger and thumb. Local anaesthetic can be infiltrated subcutaneously. Some authors advise injection of 2 ml subcutaneously, plus 1 ml as the needle is inserted into the foramen and an additional 2 ml when the needle is at its full depth of 1 inch. This block will desensitise the middle 2/3rds of the upper eyelid as well as the forehead.
Lateral – The lacrimal nerve is anaesthetised subcutaneously by inserting the needle at the lateral canthus and infiltrating along the dorsal rim of the orbit for the length of the needle. This anaesthetises the lateral canthus and lateral aspect of the upper eyelid.