MIT Media Lab researchers have developed an interactive, portable, and inexpensive solution for estimating refractive errors in the human eye.

The NETRA system uses an ordinary cell phone. The subject looks into this display at a very close range and aligns (overlaps) displayed patterns . Since the light rays from these patterns pass through different regions of the visual system, the alignment task gives a measure of the optical distortions of those regions. The subject repeats this procedure for a few meridians with appropriate variation in the patterns. The software computes the corresponding refractive error for myopia, hyperopia and astigmatism.

The low-cost system would be especially useful for the developing world.

Current prototypes using the Samsung Behold II and the Nexus One. An optical phase plate creates virtual images and achieves 0.6 and 0.4 diopter resolution respectively.

http://www.youtube.com/watch?v=gR6wMlnmc68

More info: MIT Media Lab