LONDON , England ( CNN ) -- In the developing world millions of people struggle to operate machinery , read from a blackboard , or just see the world around them , because they do n't have access to the eyeglasses they need . Self-refraction glasses let the wearer adjust the lenses to suit their vision , without the need for an optometrist . But a pair of glasses developed by Joshua Silver , a physics professor at the University of Oxford , offers an affordable solution . The glasses can be adjusted to the right strength by the wearer without the need to visit an optometrist . A major reason for that is a chronic shortage of optometrists -- in Ghana , for example , there is just one for every eight million people . That makes it incredibly difficult for ordinary people to visit an optometrist , without which it 's impossible for them to get glasses . But Silver thinks he may have come up with a solution to the problem . His self-refraction glasses mean people can correct their vision without needing an optometrist ( see Fact Box ) . `` Take a Sub-Saharan country where there is one optometrist for every million people ; those people will never see an optometrist , so how will they get eyewear ? , '' he told CNN . `` Any model of delivery of vision correction in the developing world that depends on eye care professionals wo n't work . If you find a model that does n't rely on them , then you potentially have a solution . '' Silver has been developing the glasses for over 20 years and continues to research the technology at the Center for Vision in the Developing World ( CVDW ) at the University of Oxford . He told CNN that about 80 percent of those who try the glasses are able to correct their vision , but there are limitations . They ca n't be used to correct astigmatism and it 's not known if they are suitable for children , although the CVDW is currently running a study to determine if schoolchildren can correct their own vision with their teachers ' help . So far , 30,000 pairs of self-refraction glasses have been distributed around the world , through an adult literacy program in Ghana and the U.S. Military Humanitarian and Civic Assistance ( HCA ) Program . The man behind the HCA program was Kevin White . He has now retired from the military and has set up Global Vision 2020 to distribute self-adjustable glasses . White has just returned from Liberia , where he trained 40 people from local NGOs to dispense the glasses . White sees charity organizations already working in developing countries as the key to distribution . `` If I can train people from existing networks to dispense glasses , and they can spare one day each week or month to dispense the glasses , then they can see 50 to 100 people in a day -- and that 's a way to reach a lot of people , '' White told CNN . But for the program to be sustainable , White says the next step is to train his dispensers to become trainers themselves , so that he builds a growing network of people in developing countries who can distribute the glasses . Silver estimates that one billion people in the developing world do n't have access to the glasses they need , and he has said that he would like to see all of them wearing glasses by 2020 . But he is under no illusions that he can do it alone . `` No one person or company can possibly deliver that many glasses by 2020 . There 's a big infrastructure that needs to be set up to do that , and I 'd like to see it happen , '' he told CNN . Distribution is one problem , cost is another . Currently , it cost $ 19 to manufacture a pair of self-refraction glasses , and Silver acknowledges that the price needs to come down to a few dollars a pair to make them affordable . Another issue is style . The glasses are currently functional , rather than fashionable , and that may limit their uptake , but more cosmetic versions are being developed . Silver says far more research is needed before those one billion people get their glasses , but he sees his self-refraction technology as a step toward that goal . He told CNN , `` It 's one of the world 's largest problems . There 's an immense amount of interest in solving it and self-refraction is one route that can assist with that . ''
A lack of optometrists means many in the developing world ca n't get glasses . Josh Silver has developed glasses with lenses that can be altered by the wearer . The technology could be used to provide glasses for one billion people . Global Vision 2020 is training charity workers to dispense the glasses .