Blindness is the complete absence or severe impoverishment of vision. The World Health Organization (WHO) defines blindness as acuity of less than 20/400 in the better eye (in case of unequal vision loss across the two eyes) or a visual field of less than 10° around fixation. Blindness is to be distinguished from low vision, which is defined as best-corrected acuity of less than 20/60, but better than 20/400. While blindness effectively renders vision ineffective for even the most basic tasks (such as obstacle avoidance), low vision permits some coarse visually guided skills, although it compromises more detail-oriented ones, such as reading and driving.

Over 35 million people across the world are blind, with the highest incidence (over 90%) in developing countries. Each year, 1 million ...