Visiting Vet: Cats’ eyes

A good ophthalmologic exam and special care helps this older cat with corneal sequestrum.

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Corneal sequestrum in cats usually just affects one eye. — Michelle Gerhard Jasny

Ketzeleh, a sweet older cat, came in for an appointment. Her owner reported the cat’s eyes had been a little runny for a few months. She hadn’t been too concerned since Ketzeleh had been feeling fine, but then one eye had suddenly turned cloudy white all over. I took a peek. Ketzleh’s right eye looked like a fuzzy white marble with a weird quarter-inch diameter brown spot in the middle. From a distance, one might mistake this spot for her pupil , i.e. the dark area created by the opening in the iris, which constricts and dilates as needed to let the appropriate amount of light through to the back of the eye where the retina and optic nerve are located. But it was not her pupil. This somewhat irregular brown disc of tissue sat right on her cornea (the outer surface of the eye), which is supposed to be clear as a window pane.

The eye is a complex organ. A good ophthalmologic exam involves evaluating all the structures, inside and out — cornea, anterior chamber, iris, lens, posterior chamber, and retina, as well as the surrounding conjunctiva and eyelids. But in Ketzeleh’s case, it was impossible to see anything beneath the surface. I donned my magnifying headset and turned on my brightest exam light. I have seen animals with all kinds of things stuck in their eyes — bits of sticks, burrs, other plant matter. Was this a foreign body I needed to remove? Nope. This did not look like a foreign body. It looked fixed to the corneal surface. I snapped a few photos and consulted my ophthalmology texts.

Oh, right. I hadn’t seen this in a long time, but now I remembered. Corneal sequestrum. A condition in which a piece of the cornea dies and usually turns brown or black. Initially it may be painless, but eventually the body tries to drive the sequestrum out like it would a splinter or other foreigh object. The area around the sequestrum may start to “erode” causing a corneal ulcer, which often becomes infected. In Ketzeleh’s case, the eye was already in serious trouble. The ulcer surrounding the sequestrum was badly infected and was already progressing to a stage called a “melting ulcer.” There was a risk the erosion might eventually perforate the cornea entirely. In other words, her eye could rupture.

We don’t know for sure why corneal sequestra form but several factors may be implicated. Chronic feline ocular herpes virus infection, trauma, eyelid malformations, and other problems like “dry eye” (inadequate tear production) may predispose cats to this condition. Short-faced  breeds like Persians and Himalayans are also more vulnerable, probably because of their facial conformation and bulging eyes. Signs of corneal sequestrum typically include runny eyes, squinting, redness, pawing at the eye, and the visible brown spot on the cornea, usually centrally located and affecting only one eye, though rarely both eyes may be affected.

In Ketzelah’s case, the white appearance was due to inflammation of the cornea (keratitis) as well as in the anterior chamber (uveitis). “I don’t know if we can save the vision in this eye,” I told her owner. “Or even save the eye. Your best bet would be to take her to a veterinary ophthalmologist.” Definitive treatment in an eye like this often requires surgery to remove the sequestrum. The damaged corneal tissue is debrided and then “patched” with any of a variety of very specialized techniques such as a graft. Much as I enjoy ophthalmology, this is above my pay grade. In these pandemic times, finding a specialist who could see Ketzi in a timely fashion might be challenging. In any case it would be expensive and involve multiple trips off-Island. Ketzeleh’s owner opted to start with conservative medical treatment here at home.

Over the next few weeks, we treated Ketzeleh with multiple medications. Atropine to dilate her pupil and reduce pain. Topical antibiotic drops to combat the infection. Long-acting systemic antibiotics given by injection. Lubricant ointments to keep the eye moist. Pain medication to make her more comfortable. I suggested we try a treatment called “autogenous serum.” This consists of drawing Ketzelah’s blood, letting it clot, spinning it down, and drawing off the serum which her owner then applied to the eye three times daily. I was dubious as to whether any of this would work considering how bad the eye looked initially, but much to my surprise (and gratification) nine days after we began treatment the inflammation and infection had cleared significantly. I was now able to evaluate some of the inner structures of the eye. Ketzeleh also had a condition called anterior synechia in which parts of the iris had formed adhesions, making it stuck in some areas to the inside of the cornea. This prevented the pupil from having its normal ability to dilate and constrict, but there was not much more I could do medically about this complication. The ulcer was healing well so we opted to continue our treatment plan, with frequent rechecks, and hope for the best.

Two weeks after the initial visit, the brown disc had almost completely separated from the cornea, floating on the surface, attached by just a thin thread of tissue. I gently grasped it with small forceps, snipped that thread, and removed the sequestrum. With a little supportive care from her friends, Mother Nature had sloughed the dead piece of cornea all on her own, without a surgeon’s intervention.

The prognosis is still guarded. A tiny bit of sequestrum, the size of a pinhead, remains on the cornea. Will it cause ongoing problems? Will the ulcer heal completely? How will the anterior synechia affect her? Might she develop secondary glaucoma? What underlying issue caused this to occur in the first place? As long as Ketzelah is pain-free and has vision in her other eye, her quality of life should be good. All we can do right now is keep an eye on the eye and adjust our treatments as needed.