It could appear cracked because there are actually two sections to the spectacle, so if you see a crack going horizontally across the eye, dividing it into roughly 1/3, 2/3. you may be seeing that.
I would take the snake to the vet, since you've been trying. But you _could_ put a mild hand lotion like Vaseline Intensive Care on the eye several times a day, every day, until the next shed. You basically want to make sure the eye is covered at all times. Alternatively, and better, you could look for opthalmic ointment on line, and use that.