Measuring someone for an eyeglass prescription usually requires bulky diagnostic machines or high-tech laser scanners that can cost thousands of dollars. Which means that in the developing world, vision correction is often an unattainable luxury for literally hundreds of millions of people. But a team of researchers at the MIT Media Lab has unveiled a system for prescribing eyeglasses that requires nothing more than a smartphone and a $1 plastic lens attachment.

The system was created by Media Lab student Vitor Pamplona, along with Ramesh Raskar and Manuel Oliveira, two professors at the Media Lab, and post-doc Ankit Mohan, and the inventors plan on showing it off next month at the SIGGRAPH computer-graphics conference. They’ve dubbed it the Near-Eye Tool for Refractive Assessment, or NETRA for short.

To use NETRA, a patient simply peers into a small lens attached to a smartphone, loaded with the testing app. On screen, they seen parallel red and green lines; then, they use arrow keys on the phone to adjust those lines until they overlap. After just two minutes of testing, the app spits out an eyeglass prescription.

As to next steps, the team of inventors has is planning to launch a for-profit startup, called PerfectSight, that will market and produce the device for Asian and African markets.