The World Health Organization says 285 million people are blind or visually impaired. The reason is often simple and easy to treat. A pair of glasses or cataract surgery can transform someone’s eyesight.
It is thought that four out of every five cases can be prevented or cured. Even in the poorest parts of the world there are often eye doctors in the major towns and cities.
However, says Dr Andrew Bastawrous of the London School of Hygiene and Tropical Medicine, finding patients is often the problem.
"Patients who need it most will never be able to reach hospital because they’re the ones beyond the end of the road, they don’t have income to find transport so we needed a way to find them," he told the BBC.
But he thinks he has come up with a solution that is mobile and can be used with very little training.
He is trialling a smartphone app called Peek (Portable Eye Examination Kit) on 5,000 people in Kenya. It uses the camera to scan the lens of the eye for cataracts. A shrinking letter which appears on screen is used as a basic vision test.
And it can uses the camera’s flash light to illuminate the back of the eye, the retina, to check for disease.
A patient’s records are stored on the phone, their exact location is recorded using GPS and the results can be emailed to doctors.