This question leads me to wonder about seeing in and through rain.
From visual point of view, rain is light-bending droplets moving downwards, unformly in steady rain, less uniformly if there's variable strong wind. At least human brain is pretty good at filtering out the rain and seeing the stationary background.
Is this ability just physics, and no special adaptation needed? Or is it a biological ability, our eyes and brain doing some "heavy lifting" to be able to see as far as possible in rain?
If it is biological, evolved ability, then is there difference between different animals on how well they see in rain, compared to how well they see in clear weather? Has the ability evolved rarely, or does it arise naturally and easily if it gives advantage to a species? I suppose the only interesting animals here are those, which see far in clear weather to begin with.
I'm obviously looking for some real research done on the subject, not just speculation.