Ahmed Ali, the day after his cataract surgery. He has just had the bandages removed from his eyes and can see again. Ali, 75, was blind for 5 years.

The blind have descended in droves on the Bisidimo Hospital in Eastern Ethiopia.

The Himalayan Cataract Project is hosting a mass cataract surgery campaign at the medical compound that used to be a leper colony. For one week a team from the nonprofit has set up seven operating tables in four operating rooms and they’re offering free cataract surgery to anyone who needs it.

On the first day of the campaign it’s clear that the need is great.

“We have like 700 or 800 patients already in the compound and many more appointed for tomorrow and the day after and the day after that,” says Teketel Mathiwos, the Ethiopian program coordinator for the Himalayan Cataract Project.

People hoping to get their sight restored are jammed into the compound’s main courtyard. Others spill out of an office where optometrists are prepping patients for surgery. The line to get into the actual operating theater extends all the way out of the building, up along a covered walkway and then loops around the corner of another medical building. More still are standing outside the hospital gates.

Mathiwos says some patients may have to wait a day or two for the procedure.

“They have tents here,” Mathiwos says. “We give them the food to eat and we try to take care of them as best as we can.”

Some of the patients at the Bisidimo Hospital have only one milky eye. Others are blind in both eyes.

A cataract is a condition where the natural lens in a person’s eye grows opaque. There are various things that can cause cataracts including an injury to the eye or too much exposure to bright sunlight. Some research suggest vitamin deficiencies can be a factor. Cataracts usually develop slowly and are most common in people later in life. Surgery to repair cataracts consists of removing the damaged lens from a patient’s eye and replacing it with a clear, plastic one.

Dr. Matt Oliva, an ophthalmologist from Oregon, is peering through a microscope as he makes a small incision in the top of the eye of a patient on the operating table in front of him.

“This is a gigantic one,” Oliva says he tries to maneuver the gray cataract out of the slit he just made in the patient’s eye. The cataract looks like an opaque contact lens as he plucks it out from behind the cornea. Oliva is decked out in the traditional green medical scrubs you’d expect to see in an operating room except he’s wearing the bathroom flip-flops from his hotel. Ethiopian customs seized his suitcase at the airport, accusing him of carrying too much medical equipment. Eventually the officials released his luggage but not until after he’d had to improvise his outfit for a few days.

The next thing is to put the new lens back into that exact same spot,” he says as he slides a tiny plastic lens into the incision.

“This is a lens that costs $4. It’s made out of a plastic material. It can’t go cloudy. The cataract can’t come back.”

The entire operation takes four minutes. Some more complicated cases take longer. It can be harder to work on a person with an extremely deep eye socket. Also if the patient has suffered from trachoma or some other eye disease in the past, the cataract surgery might take up to 20 minutes. But even then this is a relatively quick procedure.

“It doesn’t really cost very much money,” Oliva says, “and it’s insane that there’s so many people waiting around for cataract surgery, people that could have their sight restored by a simple and inexpensive operation.”

Oliva has been a board member of the Himalayan Cataract Project for more than a decade. He regularly does mass surgical campaigns in Asia and parts of sub-Saharan Africa.

Three local surgeons are working in the adjacent rooms, and three residents are shadowing the team. Together they can remove and replace as many as 300 cataracts a day.

But Dr. Mulu Lisanekwork, an ophthalmologist from Addis Ababa who’s working on the campaign, says the number of people with untreated cataracts in Africa is huge. Ethiopia has just over 100 eye doctors — roughly 1 for every million residents. Lisanekwork says all this untreated blindness contributes to poverty in her country.

“People stop being productive when they get cataracts. And productive people are less productive because they have to take care of their blind family members,” Lisanekwork says.

Once the surgery is finished, the patient’s eye is covered with a gauze bandage. A family member or another caregiver leads the patient to a shaded part of the hospital grounds to rest and sleep off the local anesthesia.

The next morning all the post-op patients gather on long benches in the courtyard of the hospital. Doctors and nurses move from one patient to the next, removing bandages and checking the eyes to make sure there isn’t excessive bleeding or other complications.

As Dr. Oliva pulls off the gauze covering Alimi Hassen’s eyes, the 80-year-old leaps from the bench as if startled by an apparition, startled that this operation really worked.

Hassen twirls around to take in the scene in the courtyard. As Oliva laughs, Hassen hugs the doctor. Hassen had been blind for 7 years.