摘要：Normal vision depends upon the ability of the ocular lens to change shape, ensur- ing that light is focused on the most sensi- tive part of the retina. Anyone living be- yond middle age is inevitably affected by presbyopia, an inability to focus on near objects, due to the loss of flexibility of the ocular lens. It is estimated that over half of the one billion people affected globally cannot afford the spectacles needed to correct their eyesight. Most of the people with uncorrected visual impairment live in low- and middle-income countries. 1 , 2
