Every year at his physical exam, I gaze into Bingo’s big brown eyes. Being a pug, those eyes — well — they bug out a bit, but that’s part of his charm. Adopted from the shelter at the age of two, he’s eight now and handsome as ever. This year, however, I noticed a change. “Let me get the big light,” I said, rolling the lamp around the table and shining the beam at Bingo’s face, giving me a better look at his corneas.
The cornea is the outer transparent surface of the eyeball — at least it’s supposed to be transparent, but in Bingo’s case it looked as though someone had splashed a blotch of brown paint on each eye at the inner corner closest to the nose. Bingo has pigmentary keratitis, a condition that can occur in response to a variety of different stimuli that irritate the eye, leading to the appearance of these brown opacities in the corneas. It is most common in brachycephalic dogs. That’s a fancy word that literally means “short-headed” and refers to breeds such as bulldogs, Pekinese, Shih tzus, Lhasa Apsos — and pugs. A recent study showed that as many as 82 percent of all pugs are affected with some degree of pigmentary keratitis.
So what are the different stimuli that may be irritating all these eyes? And why are our smoosh-faced friends so frequently affected? Here’s why I love ophthalmology — all the great words: buphthalmos, exophthalmus, lagophthalmos, distichiasis, trichiasis, keratoconjunctivitis sicca, entropion, to list a few. Let’s start with simple anatomy. Pugs tend to have unusually large eyeballs. That’s buphthalmos. Because of how their faces are pushed in, they also have shallow eye sockets, resulting in bulging eyeballs. That’s exophthalmos. Large, bulging eyeballs may mean that when they close their eyelids, the lids may not completely cover the globes. That’s lagophthalmus. Taken all together, what do you get? Chronically exposed corneas, irritation, and pigmentary keratitis.
“Does he sleep with his eyes open? I asked. “Or do his eyes not close all the way when he shuts them?” His owner responded that Bingo slept with eyes closed and she thought the lids covered the globes fully.
What else could lead to his corneal irritation? Looking closely, I could see that a small bit of Bingo’s lower eyelids curled inward, rubbing ever so slightly on the corneas. This is called entropion. Bingo also had very pronounced nasal folds — those adorable rolls of furry skin on his face. Bingo’s nasal folds were prominent enough that when he moved in certain ways, the fur on the folds touched his corneas. This is called trichiasis, when normally occurring hair touches the eye. Both his entropion and trichiasis could be contributing to his keratitis.
There were two more similar conditions I needed to rule out — distichiasis in which aberrant hairs grow out of little glands that line the eyelid, and ectopic cilia, abnormal eyelashes growing from the inside of the lids. Using a magnifying headset and then an ophthalmoscope, I scrutinized the margins of Bingo’s lids but could not see any evidence of these.
Now it was time to check for keratoconjunctivitis sicca. Commonly known as KCS or “dry eye,” in this condition the dog does not produce adequate tears to lubricate the eye. Constant dryness results in irritation and inflamation. We measure tear production by tucking a small strip of special calibrated paper in the corner of the eye for exactly one minute. Bingo was not thrilled with this procedure, but we were able to determine that he appeared to be making a normal amount of tears.
Some dogs, however, make sufficient quantity of tears yet still have poor “tear film quality.” In other words, they have an inherent deficiency in the viscosity of the tears, so the fluid breaks up too fast, not keeping the eye properly protected. I put a drop of fluorescein stain in each of Bingo’s eyes. This non-irritating, water-soluble dye, starts out as orange, then turns day-glo green. It is used primarily to check for corneal ulcerations but can also be used to evaluate tear film quality. With normal tear film, a drop of dye placed on the eye should take 20 seconds to evaporate, if the dog is not allowed to blink. With tear film deficiency, dry spots may appear almost immediately. Bingo was not keen on our attempts to prevent him from blinking, and I did not have much experience with this test, making it hard to assess his tear film quality. But since many ophthalmologists automatically assume that all pugs with pigmentary keratitis probably have some degree of deficiency, I did the same. There were no corneal ulcers and his intra-ocular pressure was fine.
“Optimal treatment is to correct any underlying causes,” I advised, and I offered referral to a veterinary ophthalmologist who could evaluate Bingo more thoroughly and make sure I hadn’t missed anything. Then the entropion and trichiasis could be surgically corrected. If warranted, there is also an eyelid surgery that can be done to improve coverage of the cornea. In the past, surgeons sometimes removed the pigment by shaving off the corneal surface, but this is no longer recommended as the pigment recurred in most cases.
Bingo’s owners opted to try medical treatment, as some dogs improve without surgery. I prescribed two ophthalmic ointments. The first, cyclosporine, promotes increased tear production and better film quality and also has pigment-reducing properties. The second was a combination antibiotic and anti-inflammatory steroid. Although pigmentary keratitis is not painful, it definitely affects an animal’s vision, even causing complete blindness in severe cases.
Bingo’s owners have recently noticed him being less active and having trouble going down stairs. We ruled out Lyme disease and put him on arthritis medication, but I suspect the main reason for his inactivity is that he has trouble seeing where he is going. We hope medical treatment will stop the progression of the disease or even reverse it. If not, then it’s time to see the ophthalmologist.