Sorry to bring back this somewhat old thread, but I noticed something about my 8'' silver. Well, I've got it when it was 6'' and I've had it for a little over 2 months now. When I bought him, he was in great shape with no Drop Eye. Just this week though, while I was feeding my fish, the Tiger Oscar that he is with got spooked for whatever reason and slammed into the side of the tank. Being massive, the loud bang from my Oscar scared my silver which then caused him to jump and slam into the glass lid.
Now I notice that he has a very slight case of drop eye in his right eye. Everything else is normal with him though, no loss of scales, no ripped fins and his appetite is normal.
So with that said, I believe Bderick's "collision theory" if you will, is true as I have expereinced it first hand. There were no previous signs of drop eye with my aro and his diet consisted only of flakes for the first month I've had him and then just Hikari Pellets. That and the fact that this aro is still very young.
That's it, I just wanted to vouch for the theory.