Smithsonian National Zoological Park l Friends of the National Zoo



Two Thousand Eye Exams

How do Zoo veterinarians test and tend to animals' eyesight? Let's see.

By Devin Murphy

There’s a special thrill when eyes meet at the Smithsonian’s National Zoo. Guest and resident gaze at each other, briefly and deeply bound as if nothing else existed. That current of contact is a key part of the magic of zoogoing.

Snake receives eye injection.

A snake receives an injection. (Suzan Murray/NZP)

How well, though, does the animal actually see its human admirer? That depends. Some species have stronger eyes than others. And individual animals, like humans, can have problems that impede their vision.

Keeping animals’ eyes as healthy as possible poses a big challenge for the Zoo’s keepers and veterinary staff. They’re charged with monitoring the eyesight of the roughly 2,000 animals in the Zoo’s care. Doing so takes hard work, constant vigilance, and some creative problem-solving.

Keeping an Eye on Eyes

Veterinarians monitor eye health in several ways. They conduct thorough ocular exams on almost every animal at the Zoo every two to three years as part of general checkups. During those exams, animals are anesthetized, and vets have the opportunity to examine the eyes up close, from the cornea and conjunctiva through to the retina and optic nerve. Veterinarians use ophthalmoscopes to see the eyes’ inner structures. They do so by peering through the pupil. That can be difficult in smaller animals, whose pupils are tiny. If an animal receives a clean bill of health, it will likely not need another eye exam until its next checkup.

Between checkups, of course, keepers watch for any problems in this sensitive body part. Many animals try to hide weakness or illness, but they cannot hide ocular ailments well. Keepers may notice that an animal is holding one eye shut. An eye may also look milky, be inflamed, or leak excess discharge.

When unexpected issues such as these arise, vets perform impromptu exams. Depending on the problem, vets may not immediately anesthetize an animal for an unscheduled eye exam. They may monitor the animal for a few days to see how the problem changes. Sometimes it can improve on its own, and sometimes the way the problem unfolds over a day or two can help determine what is going on and how to best treat it. They can also perform basic tests to determine if an animal can see at all.

One test that gives them a good indication if an animal has impaired vision is checking the blink reflex. “Most mammals and birds have a hard time hiding blink reflexes,” explains associate veterinarian Katharine Hope. In addition to checking the blink reflex, veterinarians can also do various things to determine if an animal can track an object visually. Hope may drop a cotton ball, toy, or favorite food item to the floor, or move a flashlight from side to side while watching to see if curious eyes follow the action.

If an animal is presenting with symptoms like excess discharge from an eye, vets may take a culture of the eye fluid and send it to the pathology lab. The results could show anything from a bacterial conjunctivitis (“pink eye”) to aspergillus (a fungal infection). Based on laboratory results and exams, veterinarians determine how to proceed with treatment.

Green tree python

Asian elephant (Mehgan Murphy/NZP)

Opening Options

Oral medications are often easier to administer to certain zoo species than topical eye drops, and oral medications can be effective at treating certain eye diseases. But administering oral medications to a wild animal— even in captivity—is not as easy as saying “Open wide.” Medications have to be hidden in food so animals take them. Depending on the dosage, that could mean temporarily altering an animal’s feeding schedule.

Hope recently treated a peahen for an aspergillus infection. The bird had been spotted holding one of her eyes closed. It was milky, and she was not able to see out of it. Hope started the bird on oral antifungal medication. To Hope’s delight, the bird responded quickly and well to the medication.

Last September, veterinarians also prescribed oral antibiotics for Mae, a 40-year-old white-cheeked gibbon. Keepers had noticed that she was squinting and had some discharge from one of her eyes. An eye culture sent to the pathology lab revealed that Mae had conjunctivitis. Oral antibiotics stopped Mae’s eye from producing excess discharge and allowed her to open it normally again.

A more direct approach to fix ocular problems is topical treatment, or eye drops. But drops are harder to administer
In 2008, a gaboon viper had fluid buildup and inflammation around one of its eyes. Suzan Murray, the Zoo’s chief veterinarian, performed surgery to drain the fluid. Afterward, the snake needed topical treatment to keep the incision clean and promote healing.

There was just one problem. The gaboon viper has two-inch fangs, the longest of any snake. They can inject enough venom to kill a human in 15 minutes. So gently dropping medicine into its eyes wasn’t an option.

“With a venomous animal safety is our number-one concern,” says Hope. “So we don’t get very close without a safe plan in place.” Instead, the veterinarians and reptile keepers relied on a special tool—a syringe pole. It’s just what it sounds like: a pole with a syringe at the end. Deftly and gingerly handled, it allows a vet or keeper to get within three feet of the snake to administer topical medications. That’s close enough to get the drops in the eye but safely out of striking distance.

Things were a bit easier with another patient the next year, male giant panda Tian Tian. He’d come down with “cherry eye” in 2009. His nictitating membrane, a bit of pink conjunctiva that acts like a third eyelid, was swelling and protruding. Being well trained to site through medical procedures in exchange for treats, Tian Tian sat patiently as the veterinarians and his keepers examined the problem and administered eye drops.

Surgical Solutions

Despite the drops, Tian Tian’s eye failed to improve, and veterinarians determined that surgery was needed to remove the protruding membrane. Planning the procedure was a challenge. Although cherry eye is a fairly common problem in domestic dogs, there was no precedent for performing this surgery on a giant panda.

The veterinary team charted the least invasive course they could. They anesthetized Tian Tian and cut away the inflamed tissue, leaving as much of the membrane intact as possible. The groundbreaking surgery was a success, and Tian Tian has not had any problems since.


Dr. Seth Koch (Suzan Murray/NZP)

Anesthetizing an animal affords vets the best opportunity to perform surgery—usually. One supersize exception came when veterinary ophthalmologist Seth Koch, who has been donating his expertise to the Zoo since 1971, was due to operate on Shanthi, an Asian elephant. She had a corneal ulcer. “We sedated her,” Koch recalls, “and she lay down on the wrong side. So the bad eye was down.”

Flipping Shanthi over wasn’t a possibility. So keepers and veterinary staff propped her head up like a car on a jack. Koch lay down on his back, slid underneath, and worked like a mechanic. It was, he says, the “funniest” situation he’s encountered at the Zoo. After half an hour, Shanthi’s eye was sutured, and the surgery was successful.

The stakes for surgery can be higher than simply improving an animal’s vision, Koch explains. “The Komodo dragon with the cataract was exciting,” he remembers. Back in 1997, the dragon, named Muffin, was slated to breed with Friendly, a larger male. But she had a cataract in one eye, and impaired vision might cause her to misread Friendly’s behavior during mating. That could make her seem uninterested, spurring him to attack.

Muffin was transferred to a veterinary hospital in Virginia, which was better equipped for the procedure. There, Koch examined Muffin’s eye with an operating microscope, then used an aspirator to clean it out and remove the cataract. The successful operation made national news.

Many Eyes, One Effort

Not every eye-care story ends neatly. Recently, veterinarians have been treating a Sinaloan milksnake. Every six months or so, fluid builds up in its eye. “We’re not 100 percent sure why it’s happening,” says Hope. An operation similar to the one performed on the gaboon viper helps to control the fluid buildup and keep the snake comfortable.

Scientists are also puzzling over why seals and sea lions are plagued with ocular ailments, often involving corneal troubles or cataracts. In general, they seem to have more eye problems than other zoo animals. Why? The answer might lie in the animals’ environment. Prolonged exposure to sunlight and freshwater or saltwater may take a toll on the marine mammals’ eyes.

Sea lions (Mehgan Murphy/NZP)

Each exam and surgery gives veterinarians an opportunity to learn more about ocular issues and health. “Each species has differences, and we’re constantly learning what those differences are,” explains Koch. “The apes are like man. The birds are reasonably alike. The big cats are like the little cats.”

For a veterinarian, variations among animals can mean the difference between peering through a pinhole-size pupil or maneuvering beneath a behemoth. Yet every exam, each procedure shares a single goal: to ensure that the eye that gazes back at yours is as healthy as possible.


—DEVIN MURPHY, the editorial intern for Smithsonian Zoogoer, is a recent graduate of Providence College.



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Smithsonian Zoogoer 40(1) 2011. Copyright 2011 Friends of the National Zoo. All rights reserved.