When Allison Corona and her friends played the card game Uno, they had a rule that green and blue were the same color. The rule was instituted because Corona, 23, has an inherited form of blindness called Leber congenital amaurosis. The light-gathering cells in her retinas don't work properly due to a mutation in a gene called RPE65. As a result, Corona's world was indistinct. During the day, she could see light, but not shadows. She saw colors, but had trouble telling them apart. After sunset the world went dark. Corona was afraid to schedule college classes after 3 p.m. because she couldn't navigate unfamiliar surroundings alone.
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