Antioxidants help neutralize free radicals, which damage the macula (the part of the eye that's damaged in macular degeneration). It has been proven that a combination of antioxidants retards the already have it, as your father does.
progress of age-related macular degeneration for those who
It hasn't yet been proven that it prevents the disease for those who don't have it, though. So different physicians have different opinions as to the wisdom of taking antioxidant supplements as a preventative measure.
If your parent does take supplements specifically labeled for age-related macular degeneration (AMD), no one else in your family should take the same vitamins, because they contain more zinc than would be recommended for everyone.