British ophthalmologist Andrew Bastawrous moved his family from London to Kenya in 2013 with $150,000 of equipment, a team of 15 people and an ambitious goal: to understand the causes of blindness in rural Africa. It didn't take long before he encountered all sorts of obstacles, including unpredictable power supplies and the regular need to run a gas-fueled generator to keep the equipment going. Many of the villages he was trying to reach had no roads and no electricity.

There had to be a better way, Bastawrous thought as he set about developing a smartphone app to help conduct high-quality eye exams without the need for heavy or expensive equipment. In the first published study on the app, called , he and colleagues report that, for a group of older Kenyans, the phone-based vision test worked just as well as the gold-standard methods used in a doctor's office.

Of the 285 million people in the world with vision impairment, 80 percent live in low-income countries. The vast majority have preventable or treatable conditions, like glaucoma or cataracts. By increasing access to simple and affordable eye tests, Bastawrous hopes to create awareness about eye conditions and, in turn, connect patients with vision-saving treatments.

"For most people, it's an accepted consequence of old age that as you get older, you lose your sight," he says. "If we can create a freely downloadable app with high-quality results, it means that hopefully more people with vision problems can be identified, particularly the most vulnerable groups."

There are two standard ways to test vision. One is with a traditional letter chart that shows progressively smaller letters as patients read down each line. A newer, more accurate method uses an electronically powered box that illuminates letters of various sizes.

The Peek vision test looks a little different. On the phone's screen, patients see just one letter: an "E" that can be displayed with the prongs facing up, down, to the left or to the right. Patients don't need to be able to read or to know the English alphabet. They just point a finger in the direction they see the E facing. If it looks like a "W," for example, when pointing up.

The test-giver, who does not need to be a trained health care worker, stands 6 feet away and simply swipes the phone to indicate the way the patient thinks the E is positioned. If the patient shakes his head because the letter is too blurry, the test-giver shakes the phone. That's the "don't know" response.

At the end of the test, which takes a little over a minute, the phone vibrates and dings. Results appear immediately on the screen and can be translated to the 20/20 scale. The app can also show the patient's level of blurriness compared to normal vision.

For the latest trial, Bastawrous' team evaluated 233 Kenyans who were 55 or older. At home, patients took two eye exams: one with the Peek app and one with a standard paper chart. The next day, the same people went to a temporary clinic, where they completed the same two tests as well as one with the newer electronic technology.

Results, which appeared Thursday in the journal JAMA Ophthalmology, showed that the Peek test was as accurate as the other two methods for testing vision. The app's test, Bastawrous adds, was as quick if not quicker than the paper chart.

The phone method has other advantages, he says, including more objectivity. While paper charts require an examiner to look frequently back and forth from the patient to the chart to check for accuracy, a test-giver holding a phone never has to make any assessments at all. The phone does all the work. And once the results are on a smartphone, they can be shared remotely with doctors who are not in the field. The app also performs retina scans and other kinds of vision tests that are undergoing their own trials.

In a follow-up study that has not yet been published, the team found that people were very accepting of phone-based vision tests, possibly because the technology is so familiar. In sub-Saharan Africa, according to the United Nations, more people have cellphones than have clean, running water.

A portable, easy-to-use vision app could be useful in settings where ophthalmologists might be scarce, like developing countries, or even for patients who want to monitor their eyesight at home, says Jeremy Keenan, an ocular infectious disease expert at the University of California, San Francisco.

"This could greatly expand the ability of public health agencies to include vision screening in their outreach programs," Keenan says. "The hope would be that this type of tool could help identify people with eye disease before they have lost too much vision and at a time when treatments are still available, though whether this will be the case needs to be studied further."

One important step that needs to be worked out: how to translate vision test results into action.

"No matter how good the technology is, it's just a test," Bastawrous says. "You have to link people to very dedicated health workers and good quality services."

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