The MIT has developed an attachment of mobile phones that allows them to perform eye tests.
Costing just a couple of dollars to manufacture, this small device clips onto the phone, and then the patient interacts with the phone to get red and green lines to intersect. After just a couple of minutes, the device and software is able to diagnose vision problems, and prepare a prescription for the patient.
This seems to be an especially useful tool in developing countries, where advanced facilities are too often non-existent.