Roughly 40    million people across the world are blind and,    for a long time, most forms of blindness were permanent    conditions. The same situation held for degenerative diseases    that affect eyesight.
    But recently, scientists have made some surprising headway into    changing that. New treatments like gene therapy, stem-cell    therapy, and even bionic implants are already starting to    restore some patients' sight. And these technologies are    expected to keep improving in the future.  
    Here's a look at all the ways scientists have tried and,    increasingly, succeeded in curing the blind:  
          Children's    Hospital of Philadelphia, Daniel Burke/AP Photo This    undated image released by the Children's Hospital of    Philadelphia shows doctors Albert Maguire, left, along with    wife Jean Bennett at the University of Pennsylvania. The two    are part of two teams of scientists in the United States and    Britain that are using gene therapy to dramatically improve    vision in four patients with an inherited eye disease that    causes blindness in children.  
    Tweaking genes is one promising route to treat    blindness.  
    In 2011, a group led by Jean Bennett of the University of    Pennsylvania     used gene therapy to treat some patients with a    congenital blindness disorder. The patients in    question all hada hereditary disease called Leber    congenital amaurosis, and they all had mutations in their RPE65    gene.The patients were each given a non-harmful virus    that could sneak a healthy copy of the gene into their eye    cells. Six out of 12 showed improvement.  
    Then, in 2014, researchers led by Robert MacLaren, an    ophthalmologist at Oxford,presented    some promising early results of a very smallstudy    of six patients at various stages of a rare, inherited disease    calledchoroideremia.    These patients all lacked a protein calledREP1, which    leads to progressive vision loss. Doctors took the gene    forREP1, put it in a non-harmful virus, and injected that    virus into the patients' eyes. All reported some improvement in    their sight.  
    "One patient, who before his treatment could not read any lines    on an eye chart with his most affected eye, was able to read    three lines with that eye following his    treatment,"wrote    Susan Young Rojahn at MIT Technology Review.  
    Commercial treatments are still a ways off, however.    Researchers first have to continue to monitor these patients to    see what happens to their vision over the long term (and check    for side effects).The FDA currently recommends     15 years of safety monitoring before trying to get a    specific gene therapy approved.  
    2) Stem cells  
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4 strategies doctors are using to cure the blind