What you need is the functional ability to perform certain tasks. It's known as a waiver of demonstrated ability and is issued by your local, friendly FAA inspector.
An instructor of mine always failed the color vision portion of the physical. In flight, however, he had no difficulty identifying aviation red and green.
The TACA pilot who landed a B737 on a New Orleans levee after a double engine flame-out due to hail only had one eye. He had been shot in the face while piloting a Cessna in El Salvador.
A remarkable bit of airmanship, argueably superior to the Hudson River landing.