Heres my guess if you look at the angles that they use in 74 the educated guess would be that he has no eyes. If he did have them we would have seen the whites of his eyes during the face panning. If you remember when neji watched Shino during the prelims his body was entirely made of bugs. Case in point he doesn't have eyes and covers them with shades simply because he doesn't want people to see that his sockets are full of bugs, rather disturbing image esp. to the children of konoha. There isn't a real answer in the anime or manga, though the manga goes to some slighter detail as to shinos past but without the flashback. I'm betting there just sockets full of bugs.