Ophthalmoscopic examination of unanesthetized cats is hampered by blepharospasm and the reflex covering of the eye by the nictitating membrane. This may be particularly annoying when the bright light of the indirect ophthalmoscope is used. If the examination of the fundi is to be frequent, then general anesthesia is undesirable because of the time, danger to the animal, and the rapid onset of corneal roughness which develops during anesthesia unless special precautions are taken.
The above difficulties were found to be circumvented for eye examination of the cat (and presumably other animals' eyes) by the prior excision of the orbicularis branch of the seventh cranial nerve. The nerve is located in an incision perpendicular to, and midway on, a line extending from the lateral canthus of the eye to the ear (Fig. 1). Approximately 1 cm. of the nerve is excised.
The orbicularis oculi muscle and nictitating membrane remain paralyzed
REINECKE RD. Facial Paralysis—An Aid for Animal Ophthalmoscopy. Arch Ophthalmol. 1961;65(4):591. doi:10.1001/archopht.1961.01840020593026