I remember a pretty nasty picture from my highschool days that if you place cancer cells in a eye, there was a horrible growth of blood cells in that too. I wonder if that's related? Let me do a google image search and see if I can dig it up.
Ah poo. After a few minutes trying to find it on google images, no avail. I think it was a rabbit eye and there was a lot of blood vessels coming from the cancerous growth. Cancer cells need nutrient rich blood, so they make vessels until they reach the blood that they need.