"The aging of the eyes seems to be very similar between humans and bonobos," Ryu said, adding that the problem could pose life-threatening challenges for wild bonobos, living as they do in the shade of the rainforest canopy.
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To investigate the phenomenon, Ryu and his colleagues measured the grooming distance of 14 wild bonobos, aged 11–14, using digital photographs. They also looked at how grooming distance varies in relation to age and sex in bonobos and compared that data with information collected on focus distances in humans.
The study, published in the journal Current Biology, found that grooming distance increased exponentially with age. This was particularly evident for a chimp named Ki, who had been videotaped some time ago. Ki's eyesight now is clearly much worse than it was when the earlier video was shot.
Ryu explained that "many scientists and doctors have suggested that the lens of the eye gets rigid with age and becomes less responsive to contraction. Also, the muscle to control the lens might weaken with age."
While primates have different body sizes and average lifespans, he said that "the general age-related tendency for decreased eye function is probably shared across primate species" and "might be universal in some mammals."
National Zoo veterinarian Katharine Hope told Seeker that staff at the zoo have suspected primate eyesight could diminish with age.
"They've noticed older primates reaching for ropes, but missing them, or appearing not to see their preferred food items," she said.
It's believed that no chimp, bonobo or other primate in a zoo, however, has ever been prescribed glasses or undergone laser surgery just to correct near or far-sightedness.
Matt Steele, public engagement supervisor at San Diego Zoo Global said that most of the animals at his zoo are endangered.
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"Unfortunately, not a lot is known about many of these species, and we are not aware of any work to evaluate vision at the level" Seeker inquired about, Steele said. "Our conservation scientists tend to focus their efforts on things that are threatening species survival."
In order for a zoo animal, such as a chimp, to wear corrective lenses, it would have to be trained extensively beforehand, Hope said.
"Primates like chimps and bonobos are very stubborn, funny and intelligent animals," she explained. "They would probably instantly tear apart the glasses and look at them thinking, 'What in the world is this?'"
On the other hand, prescription glasses and goggles are already available for dogs and cats, and are growing in popularity. Warby Barker makes stylish prescription glasses for dogs and Doggles offers their namesake prescription eyewear for pets.