PlanetCatfish.com

I was browsing my LFS's tanks again tonight and noticed a tank with 5 (extremely large) . They all had cloudy eyes (not to the point where they were extremely white, but just cloudy.) And this made me wonder, is it common for them to have that or are they sick?

no, Auchenipteridae have either skin on their eye or a very thick cornea

this is an adaptation, because they approach swimming the way an ivory ball approaches snooker

they're adapted to run headlong into anything, cause that's what they do. they're extremely good at turns and very agile and flexible, so they can even bump into a large fish, make a double take and speed off.

also: they have this retina wich reflects light. this is wellknown for most animals that are active at night; the reflecting retina makes it possible to see with very little light.
many catfishes have this, gobies and puffers too; they have these weird opal looking metallic eyes.
this adds to the "greyness" of the eye, they don't have a neat black pupil like Corydoras for example.

Most auchenipterids (and many other (cat-)fishes as well) have a protective tissue that covers their eyes, which could cause people to think the eyes are cloudy. I wouldn't worry about it.
However, if in doubt just add a picture to become 100% sure.