The head of large fish is not easily chewable, so it makes sense that we wouldn't eat them. The eyes however, depending on the fish type and how fresh it is, can be a real treat. They're juicy, fatty and sometimes even sweet. I just poke 'em out with a fork, being careful not to puncture them too much, or plently of the fluid will leak - sometimes even squirt all over the place lol
I'm not sure what you meant about the scales. I used to eat scales cooked, but raw I hate them. There are no scales in the eyes, though.