And you don't have to make an appointment

Folks at the MIT Media Lab are playing around with a prototype of Netra, a system that can identify problems with a person's eyesight using only a smartphone, software, and inexpensive optical add-ons. The system could help people who can't afford or get access to full-service optometry.

Ramesh Raskar, an associate professor at the MIT Media Lab and the leader of the Camera Culture group there, said it dawned on him that the 300 dpi resolution on a smart phone screen made it the rival of expensive, specialized devices.

Raskar said the ubiquity of smartphones is a key part of what makes Netra attractive. While other systems have been proposed to provide optometry where it isn't currently available, those systems were limited by needing expensive equipment, or by being complex enough that they had to be used by an expert.

Similar hardware add-ons could transform smart phones into inexpensive sensor devices that could serve many medical and environmental needs.