What the others said about being able to look out of the tank and down is pretty accurate. It doesn't help.
I have arowanas myself and the droop eye can be linked to quite a number of things. It can be from fatty foods, but the following is one of the main reason.
In the wild, arowanas are always looking up for food such as insects, bugs, birds, etc. on the surface on even on the limbs of plants and trees that overhang the water. So they are always looking up for food. But in a fishtank, out of captivity, no one out there has shallow fishtanks.....so, the aro in the tank does not always stay on the top, it'll swim all around looking for food or chasing tankmates. Plus, the fact that the aro can look out on all sides of the tanks does not help. That's why some people try to cover the entire tank with a black cloth, thus allowing the aro to only look up.
You can try any of the following and hope that it helps. If it's too severe, it won't really revert back:
1) Ping pong ball. If your arowana it too big for the ping pong ball, use a whiffle ball! (That's what I used)
2) Drape a dark cloth over the entire tank covering all sides...you can let light in from the top or just use your light fixture.
3) Try to feed the aro food that does not sink or goldfish where the aro will have to chase after it all over the tank. Feed it crickets which stays afloat.
Hope this all helps. If you want more info...there's an arowana forum just like this one out there. www.arofanatics.com
Gosh, I know more about arowanas than a planted tank. I can't even get rid of hair algae.