But now, a team of veterinarians from Britain has arrived to perform potentially life-changing eye surgery on the bear.
Kong is one of 93 rescued bears brought to a sanctuary outside Phnom Penh by the wildlife organization Free the Bears. With the help of local authorities, the organisation rescues about a dozen bears a year.
Kong might have gone blind from his diet in captivity, says Matt Hunt, chief executive of Free the Bears. Sweets are known to cause cataracts.
Or the bear's blindness might have been self-inflicted, Hunt says.
"Living in captivity, he could have banged his head against the wall repeatedly," he says.
The milky-eyed sun bear - a breed that gets its name from the gold sun-shaped patch of fur on its chest - now lives in a large space with two other rescued bears, each with similarly troubled pasts.
Ralph is missing a paw after being captured in a snare by wildlife traffickers. The bear's canine teeth have been clipped off.
Hefty weighed 144 kilogrammes when he was rescued, more than double the average weight of a sun bear. Hefty was rescued last year from a garment factory, after being kept in a small cage and continually fed junk food by the workers.
At the sanctuary, Hefty has slimmed down considerably due to exercise and a healthy diet of fresh fruit, vegetables, honey and termites.
The animals' new home includes swinging hammocks and a pond for swimming - both favourite bear activities.
Although Cambodia has strict laws against keeping or poaching sun bears, the practice continues.
Some are butchered and served at restaurants as bear paw soup - considered a delicacy in some cultures. Others become entertainment at hotels or karaoke parlours, or are kept as exotic pets.
"When the cuteness runs out, they keep them in a small cage in the back garden to rot, or sell them on the black market," Hunt says.
Traffickers also sell the bile from the bears' gallbladders as traditional medicine. Some send the animals to bear bile farms in Vietnam, where they are kept in cramped cages and undergo frequent extraction.
The exact number of wild sun bears in Cambodia is unknown, but Hunt says the destruction of forested areas in the country's north-east is encroaching on the bears' natural habitat.
Sun bears are classified as "vulnerable" by the Convention on International Trade in Endangered Species.
After three hours of surgery, ophthalmologist Claudia Hartley says she is pleased with how Kong's procedure has gone.
Along with five other veterinarians from Britain's Animal Health Trust, Hartley has removed a cataract from one of the bear's eyes and corrected a lens problem in the other.
"The surgery couldn't have gone better. It was technically very difficult," she says. "So it was one we took on with trepidation, but it's gone extremely well.
The operation was groundbreaking, Hartley says, and probably one of only two such eye surgeries ever performed on sun bears in the world.
Kong's operation was successful.
"It is truly incredible to see him today and watch him visually exploring the world once again," said Hunt a few days after the surgery.