I used to raise aros and find that about 90% of aros that get drop-eye are the silvers. Rarely do Asian, and Jardini's get this (but I did see a big jardini that has drop-eye a couple of weeks ago). Also, I don't know of anyone reporting aros in the wild getting drop-eye. There are many theories, fatty foods, poor water quality, tank too small etc... The only way I've seen drop-eye fixed was on a video I saw. It was an Asian aro with drop-eye and they did surgery on it. They cut a little tissue at the top of the eye away and stitched the eye back up. I don't know if people do the surgery with silvers since they are pretty cheap to buy and can be found at many LFS. I had a beautiful 24 inch silver and tried everything to prevent it. I used ping pong balls, floating toys and I actually used one of those worm-blowers found at fishing stores and forced air into the nightcrawlers I was feeding it so the worms can float. Still got drop-eye but it still was a great looking fish.