a) Define better. (Sharper, greater contrast range, better at spotting rapid motion, etc are some examples of parameters, but there's no reason to assume they'd all become 'better' by the same mechanism)
b) Melanin isn't conclusively tied to eyesight. If you search you'll find a lot of pseudo-science blogs but not much in the way of studies or even their abstracts.
_________________
The Party told you to reject the evidence of your eyes and ears. It was their final, most essential command.
If you're not careful, the newspapers will have you hating the people who are being oppressed, and loving the people who are doing the oppressing. —Malcolm X
Just a reminder: under international law, an occupying power has no right of self-defense, and those who are occupied have the right and duty to liberate themselves by any means possible.