No one was certain how much Eli could see, but for all practical purposes the 10-year-old Hogle Zoo howler monkey was blind.
On Monday morning, a team of doctors set to work removing the cataracts from Eli's eyes, replacing his natural lenses with acrylic ones designed for human children. Since Eli can't follow an eye chart, his caretakers still won't be certain exactly how clear his vision will be. But early indications are he can see.
At the very least, the doctors say, he should regain enough of his sight that he will be able to make out the shapes of other monkeys, find his own food and enjoy a much happier life at the Salt Lake City animal park where he resides.
As is the case with humans, it's unclear why some monkeys suffer cataracts - a clouding and hardening of the protein that form the eye's lens. But advances in surgical optometry have made the replacement of the natural lens a relatively simple and common procedure for humans, dogs, cats and some farm animals.
And although far fewer such surgeries have been attempted on primates, Eye Care for Animals veterinarian Nicole MacLaren said that once the surgical draping was covering Eli's thick black fur on Monday, it was pretty much the same game.
"As soon as he's draped off, it's just an eyeball and you start concentrating on that," said MacLaren, who has done hundreds of similar surgeries on other
animals. Within an hour of the procedure, "the monkey was up running around and acting like he can see," MacLaren said.
Rather than subject Eli to tests that would require anesthesia, MacLaren said she and Hogle staff will probably keep close watch on his behavior to determine his visual acuity.
Eli's lenses, donated by Texas-based Alcon Surgical, should last the rest of his life. And since his natural lens was removed in the procedure, the cataracts can't grow back.
Since Eli didn't begin to suffer from the cataracts until he was 4 years old and has retained at least a small amount of vision for most of the time since, assisting surgeon Darcy Wolsey said the monkey shouldn't have too much trouble readjusting to his restored sight.
"He won't be reading the newspaper," the Salt Lake Eye Associates optometrist lamented. But after a few days of mild irritation, she said, Eli should be able to see significantly better than he could before.