Protrusion of the Feline Nictitating Membranes
Kirk N. Gelatt, VMD
Diplomate, American College of Veterinary Ophthalmologists
Distinguished Professor of Comparative Ophthalmology
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Idiopathic bilateral protrusion of the feline nictitating membranes is a common, poorly understood ophthalmic disorder. Retraction of the nictitating membranes after use of a topical adrenergic agent such as epinephrine or phenylephrine is suggestive of a loss of sympathetic innervation such as that seen in Horner's syndrome, but other ophthalmic signs of Horner's syndrome are absent. Intraocular structures are normal, and vision is unaffected unless the nictitating membranes protrude to the extent that they cover the pupil.
Cats with this syndrome often have concurrent, watery diarrhea that precedes nictitating membrane protrusion. Some cats may have such diarrhea for weeks, though many recover from the diarrhea in a shorter time but still have nictitating membrane protrusion. A tora-like, virus has been isolated from the feces of several affected cats in England. In that study, 17 of 45 cats had nictitating membrane protrusion for more than 4 weeks, and 46 of 41 cats had diarrhea for more than 4 weeks. In 87% of the cases from multicat households, more than one cat was affected, which is suggestive of the transmission of an infectious agent.
The prognosis for this condition is good, because the diarrhea and nictitating membrane protrusion are self-limiting even though clinical signs may be long-lasting. Therapy is not specifically indicated, but if the nictitating membrane protrusion is severe, a topical adrenergic agent may be helpful.
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