Vision problems are more pervasive than most of us realize. Upwards of 285 million people worldwide are visually impaired. Many more have low or moderate visual difficulties. The number in the U.S. is expected to double by 2020, due to the aging of the baby boomer generation.
NoCoffee is a free extension for Chrome (download link), which can be helpful for understanding the problems faced by people with slight to extreme vision problems.
Via Chuck Hitchcock