MIT is/ has created a tool for optometrists by retrofitting a Nexus One with mircolens or pin-hole and shooting beams of light into an eye they will be able to find out whether the person has myopia, hypermetropia or astigmatism.
The microlens array allows the phone to create a “4D interactive high-resolution light-field display” near your eye. This virtual display creates objects and places them at varying depths ranging from 1 cm to “beyond infinity”. Basically, they’ve invented a vision test that doesn’t rely on physical distance and can be administered (one presumes) anywhere at any time.
Called PerfectSight you can read more about it here