Visiting Vet: Corneal ulceration

Just takes a little sand in the eye.

An abrasion on the surface of the eye is called ulcerative keratitis, or corneal ulceration. - Joel Mills

Zebulun was having fun playing ball with his owners this past August. I’m sure the big labradoodle is a stellar athlete, but somehow, instead of the ball ending up in his mouth, it hit him in the head. That might not have been a problem; the ball was soft, his head hard … but the ball was sandy. A clump of gritty debris got in Zeb’s eye. Then he rubbed it. Can you say “sandpaper”?

The cornea is the transparent outer portion of the eye. The main portion, called the stroma, is made primarily of collagen organized in a very precise way to keep it clear. The stroma is lined, inside and out, with thin membranes that make it waterproof. Think of the whole thing like a windshield. In order to stay transparent and allow light to come through, it depends on several qualities. It has no pigment. It has no blood vessels. But when the corneal surface is damaged, say by a dog rubbing sand in his eye, this compromises the integrity and function of the windshield.

When Zeb arrived at my office several days after the sandy ball incident, there was clearly an abrasion on the surface of his eye. This is called ulcerative keratitis, or corneal ulceration. Zeb was exhibiting all the classic symptoms. He was squinting with discomfort. Because there are more pain receptors on the surface of the cornea than deeper in the stroma, the more superficial the injury, the more painful. Zeb’s eye was red and tearing excessively from the irritation and pain. There was a hazy, whitish-gray area around the injury site. This is corneal edema. It occurs when the corneal surface is damaged, allowing fluid to seep into the stroma, altering translucency.

I pulled out a little sterile strip of paper infused with fluorescein, a water-soluble dye, and instilled a drop of this day-glo green coloring into Zeb’s eye. On a normal, intact cornea, the dye will just roll off, but where sand had rubbed away the protective waterproof corneal coating, fluorescein soaked into the exposed stroma, revealing the exact extent of the ulcer. Treatment of simple corneal ulcers is, well, simple. Topical antibiotics prevent infection. Topical atropine reduces pain and also dilates the pupil, which reduces the risk of a possible complication called synechia, in which inflammation causes adhesions inside the eye. Oral pain medications are often indicated as well. Simple corneal ulcers should heal quickly, usually within a week to 10 days. Tiny blood vessels grow in from the white part of the eye, the surface membrane creeps back over the injury restoring the integrity of the cornea, and all is well.

Or not. Although Zeb’s eye showed some improvement over the next few weeks, the ulcer did not heal promptly or completely. Persistent ulcers are no longer considered “simple.” Once they become chronic, they have several different interchangeable names, including complicated, refractory, or indolent ulcers. Regardless of what you call them, the issue is the same. The darn things just won’t heal.

During the weeks we were seeing Zebulun, we were also treating Bella, a little shih tzu suffering from small refractory ulcers in both eyes. There is likely a genetic component related to the actual corneal structure. Some breeds often develop corneal ulcers spontaneously, with no history of injury. That’s what happened to Bella. She had been dealing with recurrent, persistent ulcers off and on for quite some time.

Refractory ulcers frequently present with a rim of loose membrane around the edges of the lesion that appears to interfere with the normal healing process. Treatment involves debriding this loose membrane while simultaneously trying to “wake the eye up.” We start by applying topical anesthetic to the cornea, then rubbing it with a cotton-tipped swab to roll off the loose margins of the ulcer. We tried this with Bella. Studies indicate the success rate three weeks after this simple debridement procedure to be between 20 and 84 percent. Bella supported these statistics. One eye improved slowly. The other did not.

Zeb was seen by a veterinary ophthalmologist, who performed a more aggressive procedure called a “grid keratotomy.” This involves literally scratching the surface of the eye with a tiny needle in a tic-tac-toe pattern all around the ulcer. That’s a real wake-up call to the eye! In cooperative patients, grid keratotomy can also be done with just topical anesthesia and a good assistant to hold the dog steady, though for certain individuals, general anesthesia may be necessary. Post-keratotomy, the specialist prescribed a more aggressive topical antibiotic, as well as topical and oral pain medications. Then, the coup de grace, he put a protective contact lens in Zeb’s eye.

Dogs with refractory corneal ulcers should wear Elizabethan collars at all times to prevent self-trauma. I have seen cases in which nothing seemed to help an ulcer heal, until we insisted the patient wear an E-collar 24/7. Like magic, the eye was back to normal in a week, proving that the problem wasn’t poor healing, but that the dog was repeatedly reinjuring the cornea by rubbing it.

I wish all cases of indolent ulcers were that easy, but the reality is that these situations are typically very frustrating, and often require many months of therapy. Bella does not seem to be in pain at this point, and since we have made some progress, her owners are going to give her more time to see if she continues to improve before considering any more aggressive intervention. Zeb has healed completely, thanks to the ophthalmologist. Now he just has to work on catching the ball, instead of getting hit in the head with it.