Media playback is unsupported on your device Media caption The mobile app in action: Scanning the back of the eye

A smartphone app is as effective at testing eyesight as an optician's clinic, a trial suggests.

The team, at the London School of Hygiene and Tropical Medicine, hopes it can transform eye care for millions of people in remote parts of the world.

Trials on 233 people in Kenya, published in JAMA Ophthalmology, showed the phone produced the same results as eye charts.

More than 285 million people around the world are blind or visually impaired.

It is often easy to treat with something as simple as a pair of glasses or cataract surgery. But too often people are beyond the reach of even a basic eye exam.

The team in London, with colleagues in Scotland, modified a smartphone to develop a series of eye tests that could be used with little training and were easily portable.

The Portable Eye Examination Kit (Peek) uses the phone's camera to scan the lens of the eye for cataracts.

Its "Acuity App" uses a shrinking letter which appears on screen and is used as a basic vision test.

It uses the camera's flash to illuminate the back of the eye to check for disease.

Image copyright other Image caption Letters on the phone display function as a basic vision test

Image caption It can also scan the eye lens for cataracts

Image copyright other Image caption The phone can be used to look at the retina at the back of the eye and check the health of the optic nerve

The first clinical data from tests in Kenya show the vision test gives the same results as the rows of letters pinned to an optician's wall.

Their eyes were examined both in their homes and at an eye clinic.

Further results on scanning the retina are about to be published and are described as 'compelling'.

Dr Andrew Bastawrous, who led the project, told the BBC: "The main reason for most people not getting eye treatment is simply that they don't access the services and that's usually because the services are so far away from them or are unaffordable.

"If we can detect people with visual impairment much earlier on then we have a much greater chance of increasing awareness and ensuring they have appropriate treatment.

"So something as simple as a vision test can be part of that journey."

The phone is relatively cheap, costing around £300 rather than using bulky eye examination equipment costing in excess of £100,000.

The International Agency for the Prevention of Blindness believes the app could be a "game changer".

It has previously said: "We simply don't have the trained eye health staff to bring eye care services to the poorest communities. This tool will enable us to do that with relatively untrained people."

But even if everyone could be tested it would leave the massive problem of who is going to pay for millions of people to be treated?