This happened to me just recently. Two of my cories had their eyes pecked out, I think by some Zebra Loach I had in the tank. One of the blind fish died and the other still lives. Its quite distressing to see. I'm not sure how well a top feeder or middle feeder will cope with no eyes, but catfish seem to do alright as they smell their way to a meal anyway and have poor eyesight to begin with.