A man has a vision test done by Remote Area Medical volunteers at the joint clinic with Operation Lone Star at Palmview High School in Mission, Texas August 6, 2014. Operation Lone Star started 16 years ago to help the guard prepare for emergencies such as hurricanes or pandemics in south Texas. Since then it has expanded its medical care component, treating thousands in a region that hugs the Mexican border, including some who come because no identification papers are required. Picture taken August 6, 2014. REUTERS/Shannon Stapleton (UNITED STATES - Tags: SOCIETY HEALTH POLITICS) 

Apple Inc CEO Tim Cook speaks about the new iPad Air and the iPad mini with Retina display during an Apple event in San Francisco, California October 22, 2013. REUTERS/Robert Galbraith (UNITED STATES - Tags: BUSINESS TELECOMS SCIENCE TECHNOLOGY) 

Apple Inc CEO Tim Cook speaks about the new iPad Air and the iPad mini with Retina display during an Apple event in San Francisco, California October 22, 2013. REUTERS/Robert Galbraith (UNITED STATES - Tags: BUSINESS TELECOMS SCIENCE TECHNOLOGY) 

Philip W. Schiller, Senior Vice President of worldwide marketing at Apple Inc,
introduces the new iPad mini with retina display during an Apple event in San Francisco, California October 22, 2013. REUTERS/Robert Galbraith (UNITED STATES - Tags: BUSINESS TELECOMS SCIENCE TECHNOLOGY)

Apple Inc CEO Tim Cook speaks about the new iPad Air and the iPad mini with Retina display during an Apple event in San Francisco, California October 22, 2013. REUTERS/Robert Galbraith (UNITED STATES - Tags: BUSINESS TELECOMS SCIENCE TECHNOLOGY) 

Blind capoeira teacher Joao Kanoa jokes with one of his students after giving classes at his home at the Fallet slum, in Rio de Janeiro March 2, 2013. Kanoa says he lost his vision at work seventeen years ago when the change of temperature inside a cold-storage room damaged his retina. Picture taken March 2, 2013. REUTERS/Pilar Olivares (BRAZIL - Tags: SOCIETY) 

Blind capoeira teacher Joao Kanoa searches around for his things before giving classes at the Fallet slum, in Rio de Janeiro April 12, 2013. Kanoa says he lost his vision at work seventeen years ago when the change of temperature inside a cold-storage room damaged his retina. Picture taken April 12, 2013. REUTERS/Pilar Olivares (BRAZIL - Tags: SOCIETY) 

Blind capoeira teacher Joao Kanoa plays with a cat at his home at the Fallet slum, in Rio de Janeiro May 8, 2013. Kanoa says he lost his vision at work seventeen years ago when the change of temperature inside a cold-storage room damaged his retina. REUTERS/Pilar Olivares (BRAZIL - Tags: SOCIETY) 

Blind capoeira teacher Joao Kanoa (L) gathers with his students after a session outside his home at the Fallet slum, in Rio de Janeiro April 12, 2013. Kanoa says he lost his vision at work seventeen years ago when the change of temperature inside a cold-storage room damaged his retina. Picture taken April 12, 2013. REUTERS/Pilar Olivares (BRAZIL - Tags: SOCIETY) 

Blind capoeira teacher Joao Kanoa (L) is helped by a student as they walk in the Fallet slum, in Rio de Janeiro May 8, 2013. Kanoa says he lost his vision at work seventeen years ago when the change of temperature inside a cold-storage room damaged his retina. REUTERS/Pilar Olivares (BRAZIL - Tags: SOCIETY) 

Blind capoeira teacher Joao Kanoa performs inside a "roda" (wheel) during a session at the Fallet slum, in Rio de Janeiro May 8, 2013. Kanoa says he lost his vision at work seventeen years ago when the change of temperature inside a cold-storage room damaged his retina. REUTERS/Pilar Olivares(BRAZIL - Tags: SOCIETY) 

Blind capoeira teacher Joao Kanoa is guided by his students as he returns home after a session at the Fallet slum, in Rio de Janeiro April 26, 2013. Kanoa says he lost his vision at work seventeen years ago when the change of temperature inside a cold-storage room damaged his retina. Picture taken April 26, 2013. REUTERS/Pilar Olivares (BRAZIL - Tags: SOCIETY) 

Blind capoeira teacher Joao Kanoa performs inside a "roda" (wheel) during a session at the Fallet slum, in Rio de Janeiro April 26, 2013. Kanoa says he lost his vision at work seventeen years ago when the change of temperature inside a cold-storage room damaged his retina. Picture taken April 26, 2013. REUTERS/Pilar Olivares (BRAZIL - Tags: SOCIETY) 

Blind capoeira teacher Joao Kanoa (L) plays the berimbau during a session at the Fallet slum, in Rio de Janeiro April 12, 2013. Kanoa says he lost his vision at work seventeen years ago when the change of temperature inside a cold-storage room damaged his retina. Picture taken April 12, 2013. REUTERS/Pilar Olivares (BRAZIL - Tags: SOCIETY) 

Blind capoeira teacher Joao Kanoa plays the berimbau during a session at the Fallet slum, in Rio de Janeiro April 12, 2013. Kanoa says he lost his vision at work seventeen years ago when the change of temperature inside a cold-storage room damaged his retina. Picture taken April 12, 2013. REUTERS/Pilar Olivares (BRAZIL - Tags: SOCIETY) 

Blind capoeira teacher Joao Kanoa ties a knot as he wears his capoeira gear before giving classes at the Fallet slum, in Rio de Janeiro March 2, 2013. Kanoa says he lost his vision at work seventeen years ago when the change of temperature inside a cold-storage room damaged his retina. Picture taken March 2, 2013. REUTERS/Pilar Olivares(BRAZIL - Tags: SOCIETY) 

Blind capoeira teacher Joao Kanoa reaches for a towel at his home before giving classes, at the Fallet slum in Rio de Janeiro April 12, 2013. Kanoa says he lost his vision at work seventeen years ago when the change of temperature inside a cold-storage room damaged his retina. Picture taken April 12, 2013. REUTERS/Pilar Olivares (BRAZIL - Tags: SOCIETY) 

A man tries out the camera on an iPad mini during the launch of the iPad mini and iPad with Retina display Wi-Fi models in Los Angeles, California, November 2, 2012. The iPad mini is being launched in 34 countries today. REUTERS/David McNew (UNITED STATES - Tags: SOCIETY BUSINESS) 

Employees at an Apple Store prepare for the launch of the iPad mini and iPad with Retina display Wi-Fi models before dawn in Los Angeles, California, November 2, 2012. The iPad mini is being launched in 34 countries today. REUTERS/David McNew (UNITED STATES - Tags: SOCIETY BUSINESS) 

An iPad mini is seen during the launch of the iPad mini and iPad with Retina display Wi-Fi models in Los Angeles, California, November 2, 2012. The iPad mini is being launched in 34 countries today. REUTERS/David McNew (UNITED STATES - Tags: SOCIETY BUSINESS) 

People look at iPad minis during the launch of the iPad mini and iPad with Retina display Wi-Fi models in Los Angeles, California, November 2, 2012. The iPad mini is being launched in 34 countries today. REUTERS/David McNew (UNITED STATES - Tags: SOCIETY BUSINESS) 

People wait in line for an Apple Store to open during the launch of the iPad mini and iPad with Retina display Wi-Fi models in Los Angeles, California, November 2, 2012. The iPad mini is being launched in 34 countries today. REUTERS/David McNew (UNITED STATES - Tags: SOCIETY BUSINESS) 

A woman leaves an Apple Store with purchases during the launch of the iPad mini and iPad with Retina display Wi-Fi models in Los Angeles, California, November 2, 2012. The iPad mini is being launched in 34 countries today. REUTERS/David McNew (UNITED STATES - Tags: SOCIETY BUSINESS) 

Ernest Kahn does yo-yo tricks in the pre-dawn hours while waiting for an Apple Store to open during the launch of the iPad mini and iPad with Retina display Wi-Fi models in Los Angeles, California, November 2, 2012. The iPad mini is being launched in 34 countries today. REUTERS/David McNew (UNITED STATES - Tags: SOCIETY BUSINESS) 

A man holds an iPad mini during the launch of the iPad mini and iPad with Retina display Wi-Fi models in Los Angeles, California, November 2, 2012. The iPad mini is being launched in 34 countries today. REUTERS/David McNew (UNITED STATES - Tags: SOCIETY BUSINESS) 

Apple Store employees get an iPad mini for a customer during the launch of the iPad mini and iPad with Retina display Wi-Fi models in Los Angeles, California, November 2, 2012. The iPad mini is being launched in 34 countries today. REUTERS/David McNew (UNITED STATES - Tags: SOCIETY BUSINESS) 

An Apple Store employee carries boxes of iPad minis during the launch of the iPad mini and iPad with Retina display Wi-Fi models in Los Angeles, California, November 2, 2012. The iPad mini is being launched in 34 countries today. REUTERS/David McNew (UNITED STATES - Tags: SOCIETY BUSINESS) 

People enter an Apple Store as the doors open for the launch of the iPad mini and iPad with Retina display Wi-Fi models in Los Angeles, California, November 2, 2012. The iPad mini is being launched in 34 countries today. REUTERS/David McNew (UNITED STATES - Tags: SOCIETY BUSINESS) 

Greek Prime Minister Antonis Samaras attends a swearing-in ceremony at the presidential palace in Athens July 5, 2012. Samaras, 61, attended the ceremony after two weeks recovering from a surgery to repair a damaged retina at his residency. REUTERS/John Kolesidis (GREECE - Tags: POLITICS BUSINESS) 

Apple's Senior Vice President of Worldwide Marketing, Phil Schiller, speaks about the icons for new features; the retina display, quad core chip, a new camera with face detection, HD video, Siri and 4G LTE service for the new iPad during an Apple event in San Francisco, California March 7, 2012. REUTERS/Robert Galbraith (UNITED STATES - Tags: SCIENCE TECHNOLOGY) 

A Kodak Retina camera is seen in a photo store in London January 19, 2012. Eastman Kodak Co, the photography icon that invented the hand-held camera and helped bring the world the first pictures from the moon, has filed for bankruptcy protection, capping a prolonged plunge for one of America's best-known companies. REUTERS/Stefan Wermuth (BRITAIN - Tags: BUSINESS) 

A Kodak Retina camera is seen in a photo store in London January 19, 2012. Eastman Kodak Co, the photography icon that invented the hand-held camera and helped bring the world the first pictures from the moon, has filed for bankruptcy protection, capping a prolonged plunge for one of America's best-known companies. REUTERS/Stefan Wermuth (BRITAIN - Tags: BUSINESS) 

U.S. soldier PFC Jeremy Strabbing from Task Force "No Fear" Alpha Co 2-27 Infantry "The Wolfhounds" gets the retina scan of a resident, next to assorted types of ordnance at Combat Outpost (COP) Pirtle King in Ghaziabad district in Kunar province, eastern Afghanistan September 23, 2011 REUTERS/Erik De Castro (AFGHANISTAN - Tags: MILITARY CIVIL UNREST CONFLICT) 

A U.S. soldier from 3rd Platoon, Bravo Company, 1-22 Infantry Batallion takes a retina scan of a villager during a patrol in Shingkay village in Kandahar province in southern Afghanistan October 4, 2010. REUTERS/Erik de Castro (AFGHANISTAN - Tags: MILITARY POLITICS CIVIL UNREST) 

A U.S. soldier from 3rd Platoon, Bravo Company, 1-22 Infantry Batallion takes a retina scan of a villager during a patrol in Shingkay village in Kandahar province in southern Afghanistan October 4, 2010. REUTERS/Erik de Castro (AFGHANISTANPOLITICS UNREST - Tags: MILITARY POLITICS CIVIL UNREST IMAGES OF THE DAY) 

15-month-old Tanishka has her eyes examined inside a operation theatre during a free treatment for poor patients to mark World Retinoblastoma Awareness week in the southern Indian city of Hyderabad May 12, 2010. Retinoblastoma is the most common primary ocular malignancy (eye cancer) of childhood, a doctor said. REUTERS/Krishnendu Halder (INDIA - Tags: HEALTH) 

Anirban, 4, who is suffering from retinoblastoma, waits to get his eyes examined during a free treatment for poor patients to mark World Retinoblastoma Awareness week in the southern Indian city of Hyderabad May 12, 2010. Retinoblastoma is the most common primary ocular malignancy (eye cancer) of childhood, a doctor said. REUTERS/Krishnendu Halder (INDIA - Tags: HEALTH) 

A U.S. Army soldier scans an eye of an Afghan suspect at a local police station in the town of Kandahar, southern Afghanistan March 24, 2010. REUTERS/Shamil Zhumatov (AFGHANISTAN - Tags: MILITARY CONFLICT CRIME LAW) 

A U.S. soldier of 2nd Squadron, 14th Cavalry takes a retina scan of a refugee at a joint U.S.-Iraqi military security station in Sab al-Boor near Baghdad December 15, 2008. Residents who fled due to sectarian violence for the past two years from Sab al-boor are screened in the U.S.-Iraqi military station before they can return to their areas. REUTERS/Erik de Castro (IRAQ) 

A refugee shows his eye during a retina scan at a joint U.S.-Iraqi military security station in Sab al-Boor near Baghdad December 15, 2008. Residents who fled due to sectarian violence for the past two years from Sab al-Boor are screened in the U.S.-Iraqi military station before they can return to their areas. REUTERS/Erik de Castro (IRAQ) 

A U.S. soldier of 2nd Squadron, 14th Cavalry takes a retina scan of a refugee with the assistance of an Iraqi soldier at a joint U.S.-Iraqi military security station in Sab al-Boor near Baghdad December 15, 2008. Residents who fled due to sectarian violence for the past two years from Sab al-boor are screened in the U.S.-Iraqi military station before they can return to their areas. REUTERS/Erik de Castro (IRAQ) 

An Iraqi man shows his eyes to a U.S. soldier from Bravo Company, 1-22 Infantry Battalion (not pictured) during a retina scan to register his personal data during a mopping-up operation at the edge of the Shiite-dominated neighbourhood of Shulla in Baghdad May 20, 2008. REUTERS/Oleg Popov (IRAQ) 

A U.S. soldier from Bravo Company, 1-22 Infantry Battalion performs a retina scan to register personal data of Iraqi men during a house-to-house search on the edge of Baghdad's Shiite dominated neighbourhood of Shulla, May 18, 2008. Picture taken May 18, 2008. REUTERS/Oleg Popov (IRAQ) 

A U.S. soldier from Bravo Company, 1-22 Infantry Battalion performs a retina scan to register personal data of Iraqi men during a house-to-house search on the edge of Shiite dominated Baghdad's neighbourhood of Shulla, May 18, 2008. Picture taken May 18, 2008. REUTERS/Oleg Popov (IRAQ) 

A U.S. soldier from Bravo Company, 1-22 Infantry Battalion performs a retina scan to register personal data of Iraqi men during a house-to-house search on the edge of Shiite dominated Baghdad's neighbourhood of Shulla, May 18, 2008. Picture taken May 18, 2008. REUTERS/Oleg Popov (IRAQ) 

A French eye surgeon performs an operation on a patient with a detached retina (retinal detachment surgery) in an operating room at the Ambroise Pare hospital in Marseille, on April 3, 2008. REUTERS/Jean-Paul Pelissier (FRANCE) 

A French eye surgeon performs an operation on a patient with a detached retina (retinal detachment surgery) in an operating room at the Ambroise Pare hospital in Marseille, on April 3, 2008. REUTERS/Jean-Paul Pelissier (FRANCE) 

A French eye surgeon uses a microscope as he performs an operation on a patient with a detached retina (retinal detachment surgery) in an operating room at the Ambroise Pare hospital in Marseille, on April 3, 2008. REUTERS/Jean-Paul Pelissier (FRANCE) 

A French eye surgeon performs an operation on a patient with a detached retina (retinal detachment surgery) in an operating room at the Ambroise Pare hospital in Marseille, on April 3, 2008. REUTERS/Jean-Paul Pelissier (FRANCE) 

French eye surgeons perform an operation on a patient with a detached retina (retinal detachment surgery) in an operating room at the Ambroise Pare hospital in Marseille, on April 3, 2008. REUTERS/Jean-Paul Pelissier (FRANCE) 

French eye surgeons perform an operation on a patient with a detached retina (retinal detachment surgery) in an operating room at the Ambroise Pare hospital in Marseille, on April 3, 2008. REUTERS/Jean-Paul Pelissier (FRANCE) 

French eye surgeons perform an operation on a patient with a detached retina (retinal detachment surgery) in an operating room at the Ambroise Pare hospital in Marseille, on April 3, 2008. REUTERS/Jean-Paul Pelissier (FRANCE) 

French eye surgeons perform an operation on a patient with a detached retina (retinal detachment surgery) in an operating room at the Ambroise Pare hospital in Marseille, on April 3, 2008. REUTERS/Jean-Paul Pelissier (FRANCE) 

French eye surgeons perform an operation on a patient with a detached retina (retinal detachment surgery) in an operating room at the Ambroise Pare hospital in Marseille, on April 3, 2008. REUTERS/Jean-Paul Pelissier (FRANCE) 

French eye surgeons perform an operation on a patient with a detached retina (retinal detachment surgery) in an operating room at the Ambroise Pare hospital in Marseille, on April 3, 2008. REUTERS/Jean-Paul Pelissier (FRANCE) 

French eye surgeons perform an operation on a patient with a detached retina (retinal detachment surgery) in an operating room at the Ambroise Pare hospital in Marseille, on April 3, 2008. REUTERS/Jean-Paul Pelissier (FRANCE) 

A nurse prepare a patient with a detached retina (retinal detachment surgery) for an eye operation at the Ambroise Pare hospital in Marseille, on April 3, 2008. REUTERS/Jean-Paul Pelissier (FRANCE)