Hey Del great article. I would like to shed some light on what I think causes Drop Eye.
Ive raised several Arowanas over the years and my observations lead me to believe that drop eye is caused by a collision with some hard object in the aquarium. Aquarium tops are probably the biggest culprit. Arowanas can generate an amazing amount of power for jump out of the water and in the wild Arowanas do jump out of the water to catch prey on over hanging braches. Due to their jumping ability an aquarium top is a must. Problem is during an Arowanas life he will probably hit the top of the aquarium several times and possibly causing an injury his eye(s).
Currently I have a Silver Arowana about 2 feet long and it suffers from a drop eye with his right eye being worse than the left. The drop eye in the Arowanas right eye was caused by him going after a goldfish I just put in the tank. He darted after this goldfish and in doing so he hit the aquarium top really hard. After the impact I immediately noticed his right eye was bulging out a little at the top thus making his eye point downward. Besides the eye bulging out at the top the Arowana appeared uninjured. That injury occurred about a year and a half ago and ever since that incident he has always looked down (drop eye). Im guessing that an eye injury of this type is pretty much permanent.
What about diet causing drop eye? I feed my Arowana goldfish, floating cichlid pellets, floating algae tablets, flake food, and an occasional cricket. My Arowana has great color and great finnage so I will rule out diet as a cause of any drop eye.
As for the suggestions that drop eye is caused by Arowanas looking at their reflection at the bottom tank. I have a thick gravel bottom but I do have glass sides on my tank. So if drop eye was caused by an Arowana looking at his reflection then my Arowana should suffer from straight eye or forward eye.