The provision of glasses for schoolchildren with visual problems and adults with presbyopia and other conditions requiring corrective glasses is taken for granted in most industrial countries, but in many developing countries the importance of glasses in enabling these people to lead socially and economically satisfactory lives is just beginning to be acknowledged. The expansion of education is one factor in this growing awareness: learning is difficult, if not impossible, for children and adults with visual defects. Yet glasses are often unobtainable because of their high cost; people sometimes resort to purchasing a pair of cheap, second-hand glasses that may be available in a local market.