By Patrice Scott
Tuesday, May 30, 2006
Known for their keen eyesight, bald eagles can see a rabbit from a mile
away, and their vision is at least four times sharper than that of a
human with perfect eyesight. When a bald eagle swoops down from several
hundred feet to catch a fish, the bird's powerful talons skewer its prey
with 1,000 pounds of pressure per square inch.
When Alaska, a 32-year-old female bald eagle at Sunset Zoo in Manhattan,
Kan., wasn't eating food unless it was placed directly in front of her,
zookeepers knew there was a problem. And, her eyes had a cloudy
appearance, the telltale sign of cataracts.
Ryan Gulker, general curator at Sunset Zoo, said Alaska's situation
progressed rapidly. "It was surprising how quickly this happened."
Exotic animal medicine veterinarians at the Veterinary Medical Teaching
Hospital at Kansas State University confirmed Alaska had cataracts while
performing an annual wellness examination. Zookeepers and veterinary
specialists monitored her situation, which was clearly worsening.
"The keepers observed that she was bumping into obstacles, like branches
and perches, when she tried to change her position or when she'd get
startled," said Dr. Connie Ketz-Riley, clinical assistant professor in
exotic animal, wildlife and zoo animal medicine. "She wasn't consuming
food unless it was right at her feet."
Dr. Rachel Allbaugh, ophthalmology resident, said Alaska was fortunate
to be in captivity given her handicap. "Were she in the wild, she would
have starved to death."
Dr. Harriet Davidson, professor of ophthalmology, explained to
zookeepers that Alaska's vision could be corrected with
phacomulsification, a procedure to remove cataracts. She said that
cataracts impair vision by robbing the eye of light. "By removing the
opaque lens, or cataract, light is able to penetrate to the retina and
this is what allows vision."
The veterinary specialists met with zookeepers and presented their
options.
"After consulting with the veterinarians and the specialists in the
ophthalmology department, we weighed the pros and cons and the pros
won," Ryan said. "Even though she is an aged bird, we could improve her
quality of life."
Once the procedure was scheduled, it required intense preparation to
minimize the bird's stress. "We did everything possible to reduce her
time in confinement for surgery," Ketz-Riley said. "We caught her
mid-morning and brought her to the teaching hospital. She was given an
ophthalmologic exam to evaluate the structure of the eye and retinal
function. Her retinal function was normal in both eyes so we decided to
proceed."
Surgery offered abundant challenges because of the bird's eye structure,
age and stress level. Because of these factors, there would be
additional risks associated with anesthesia.
Alaska was placed in a deep plane of anesthesia because of her
complicated eye structure. An eagle's eyelids close during sleep, but
they also have a nictitating membrane, or third eyelid, that sweeps dirt
and dust from the cornea about every three seconds. "When anything
touches the eye, it triggers muscle movement and the third eyelid
protrudes," Ketz-Riley said. "This needed to be neutralized for surgery.
We had to keep her in a deeper anesthetic plane, which increases the
risk for the bird."
For one and a half hours, Davidson and Allbaugh performed microsurgery
on Alaska. Ketz-Riley said they knew soon after surgery that it was a
success. "The surgery could not have gone better. As soon as keepers put
her food down, she went right after it."
Three weeks later, the specialists were able to examine Alaska and
evaluate her progress. "We were thrilled at how great her eyes looked,"
Allbaugh said, adding it was difficult waiting so long to examine the
bird. "We wanted to examine her, but we didn't want to take the chance
of stressing her or causing her to tear her sutures that are the size of
a strand of hair."
Now when visitors to Sunset Zoo stop by to see Alaska, she will be
looking back at them, too.