If you have retina tears, then be careful about things like getting smacked in the head (that can loosen things up in there), and be sure to get them checked regularly to make sure you're not at risk of a detachment. You also have to watch out for the fingers in the eyes; I have to start looking for a good pair of sports goggles or something. Annoying task, but it must be done.
From what I understand, as long as you're vigilant, and aware of symptoms, and are good about going to the retina specialist regularly, it is possible to train full-contact sports like Krav Maga.
Darn kids! Get off my bandwidth!