User blog comment:Lord Loss/Monster Hunter Theory... Blog/@comment-6050823-20140725161001/@comment-4212769-20140728124341

Actually it's very likely that Ceadeus can't see very much with its eyes as well, considering how small they are and that it lives in the deep sea. So echolocation is a possibility but it could also have light receptors on horns or face so that it can perceive the glowing of other monsters and Ceadei still. Could be a combination of both.