Eyeglass prescriptions assessed on a cell phone, for the 3rd world

I was amazed at this. A cell phone add-on that can assess refractive index in a few minutes as the user lines up parallel lines. Does it seem like it'd actually work?

The article is called "Cheap, Portable Cell Phone Add-on Allows for Vision Tests Anywhere"
http://www.popsci.com/technology/article/2010-06/cheap-portable-cell-phone-add-allows-vision-tests-anywhere

It reminded me of a similar innovation from an article a few years ago that modified a cell phone into a microscope for blood smears to diagnose infectious diseases in the third world. However, that technology seemed to have less widespread applicability, required technical skill to obtain the smear, and required sending the cell phone photo to a central lab for diagnosis.

http://www.newsweek.com/2009/08/11/dial-d-for-diagnosis.html