The optician's clinic that fits in your pocket
15 August 2013 Last updated at 00:26 BST
A modified smartphone is being tested in Kenya to see if it can prevent blindness in some of the poorest parts of the world.
The kit, designed by a researcher from the London School of Hygiene and Tropical Medicine, can scan the back of the eye, check for a cataract and perform a basic vision test.
The World Health Organization says 285 million people are blind or visually impaired.
Health and science reporter James Gallagher went to a London Park with a willing volunteer to find out how simple the kit is to use.