By Andrew Liszewski
If you’ve ever had your eyes tested at an Optometrist, you’ll understand why it’s difficult to get the equipment they use (namely a lens-based Phoropter or a laser-based Aberrometer) into remote, developing nations, where vision problems aren’t dealt with and often lead to blindness. But a team from MIT’s Media Lab, led by Professor Ramesh Raskar, has developed a low-cost alternative for testing vision using a small plastic device they’ve developed that clips onto a cellphone and takes advantage of today’s high resolution LCD displays.
The patient looks into a small lens and uses the phone’s buttons to adjust the position of sets of parallel green and red lines until they just overlap. This ‘test’ is done eight times for each eye, with the lines at different angles, and once completed an app on the phone analyzes the results and provides a prescription, all in about 2 minutes. Here’s Professor Raskar’s explanation of how and why the system works.
The prototype system Raskar and his students developed as a result of that insight has an array of tiny lenses and a grid of pinholes that, combined with the software on the phone, “forces the user to focus at different depths” so the eye’s focusing ability can be measured. 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
Even more impressive is that the snap-on plastic device needed to conduct the tests only costs about $1-2 to produce in minimal quantities, and large scale production could easily bring the cost down to just a few cents, which is exactly what they plan to do. The system will begin field-testing in Boston this Summer, then later in developing countries, and they’ve applied for a patent for the technology and plan to eventually mass produce the device under a for-profit company called PerfectSight.
And if you want a more detailed, and more visual, explanation of how the system works, make sure to check out the video I’ve included after the jump.