The star of a new HBO documentary called Open Your Eyes is wizened and gray, although she's most likely only in her 60s – exact ages can be hard to figure out in Nepal, where she lives. She lives with her husband and son and young granddaughter. Playing with the child in an early scene in the film, she says, "When I feel her toes, it feels like mine."

But she doesn't know for sure. That's because Manisara's eyes do not see. She has cataracts — the world's No. 1 cause of blindness, responsible for robbing some 20 million people of their sight. Leading causes of cataracts are exposure to sunlight, smoking and drinking alcohol. Over time, the eye's lens grows opaque; vision clouds and disappears.

Her husband, Durga, has also lost his sight to cataracts. So the two of them cannot help tend to the family livestock or agricultural plots. "Even getting water is hard," says Durga. "I just stay home and do nothing."

In the Western world, a simple surgery can restore vision. An eye surgeon cuts a slit in the eye, removes the lens and replaces it with a plastic "intraocular lens." The typical cost, around $1,500 in the U.S., is covered by insurance.

In low- and middle-income countries, millions of people don't have easy access to the surgery, says Dr. Norman Kleiman, a researcher at Columbia University's Mailman School of Public Health who studies cataracts. Maybe they live in remote parts where there's no eye surgeon available – the whole country of Bangladesh has only 500 ophthalmologists for its 160 million-plus citizens, he notes. Or maybe they can't afford the cost of the procedure.

Meanwhile, the plastic lens itself is quite cheap — it can be produced for under $2. So nonprofit groups are stepping in. And that's the story in Open Your Eyes, a documentary directed by Irene Taylor Brodsky, whose film about her deaf parents, Hear and Now, won a Peabody Award.

This documentary, which premieres Monday at 7:30 p.m., is set in the Himalayan mountains of Nepal and follows the efforts of the Seva Foundation to find people with cataracts and bring them to a hospital for free surgery by a volunteer doctor. The foundation is one of about a half-a-dozen groups that tackle the problem of cataracts with good results, says Kleiman. Representatives go door to door in villages, looking for possible patients. That's how they found Manisara and Durga.

In the film, the couple take a long walk (and then a ride) to the nearest town with a hospital. One scene shows the couple as they inch down a rocky path from their home. Manisara is barefoot — that's the way of her generation — and complains a lot: "I can't walk. My legs hurt. Everything hurts."

It's not giving away too much to say that yes, Manisara and Durga get the surgery, and it works. Indeed, the World Health Organization characterizes cataract surgery as "very successful in restoring sight."

Manisara is transformed when her vision returns. Years fall off her face. She stops griping about her aches and walks across a narrow bridge with a purposeful stride, playing to the camera: "I really need to show off," she says.

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