Until now, an eye test has meant a trip to the optometrist for most people. NETRA, from MIT's Media Lab, is set to change that. Combined with a modern mobile phone, the device, currently thought to be producible for US$2 at most – but expected to drop significantly in cost when made in bulk – allows eye glass prescriptions to be produced simply and quickly in any location. Preliminary testing has shown that "it can achieve results comparable to the standard aberrometer test" and clinical trials are due to begin shortly. Initially targeting parts of Africa and Asia, the company responsible for manufacture, PerfectSight, is expecting the product to be a boon for the developing world, where the sophisticated equipment currently required for eyesight tests has been cost prohibitive.

Here's how it works. Looking through the lens, the patient lines up parallel sets of red and green lines eight times for each eye. That's it. It takes about two minutes. The rest is up to the software on the phone, which creates the prescription data. The test forces the user to focus at different depths, allowing for the detection of "nearsightedness, farsightedness, astigmatism, and age-related vision loss."

What sets NETRA apart, according to postdoctoral research associate Ankit Mohan, is its lack of moving parts. The device takes advantage of the proliferation of cell phones with high-resolution displays. Ultimately the aim is to include such a display in the device itself, allowing its uses to be expanded to include testing for other conditions such as cataracts.

Conceived as a result of developer Associate Professor Ramesh Raskar showing his wife a previous invention, "Bokode", it's a great example of how game changing technologies can come from coincidental events... and in this case, potentially make a difference to the estimated two billion people worldwide who have refractive errors.