Cheap and Easy Eye Tests On Your Cell Phone

Researchers at MIT have developed a method of using a basic cell phone coupled with a cheap and simple plastic device clipped onto the screen to estimate refractive errors and focal range of eyes. Because of its simplicity and the fact that soon just about everyone will have access to a mobile phone, eye exams may become available to the whole world at little to no cost.

In its simplest form, the test can be carried out using a small, plastic device clipped onto the front of a cellphone’s screen. The patient looks into a small lens, and presses the phone’s arrow keys until sets of parallel green and red lines just overlap. This is repeated eight times, with the lines at different angles, for each eye. The whole process takes less than two minutes, at which point software loaded onto the phone provides the prescription data. The device is described in a paper by MIT Media Lab Associate Professor Ramesh Raskar, Visiting Professor Manuel Oliveira, and Media Lab student Vitor Pamplona (lead author of the paper) and postdoctoral research associate Ankit Mohan, that will be presented in late July at the annual computer-graphics conference SIGGRAPH.
The device uses an optical system derived from one some team members developed last year as a way of producing tiny barcodes (called Bokode) that could provide a large amount of information. Raskar explains that he had demonstrated that barcode device to many people, but when he showed it to his wife she had trouble seeing its patterns. He quickly realized that others he had shown it to had been wearing their glasses or contact lenses, but his wife had been looking into it directly and it had revealed the imperfections in her vision. “I said, ‘Wow, maybe you don’t need such an expensive device'” as those presently being used to test people’s vision, Raskar recalls.
Essentially, Raskar explains, the test works by transforming any blurriness produced by aberrations in the eye into an array of separate lines or dots instead of a fuzzy blob, which makes it easier for the user to identify the discrepancy clearly. Rather than estimating which of two views looks sharper, as in conventional eye tests, the user adjusts the display to make the separate lines or dots come together and overlap, which corresponds to bringing the view into sharp focus. The underlying principle is similar to that used by new “adaptive optics” systems that have recently allowed ground-based telescopes to exceed the performance of the Hubble Space Telescope; these sometimes use the same kind of Shack-Hartmann sensors used in eye testing aberrometers.