I respectfully disagree about ALWAYS getting shed off of the eyes. It is my experience and educational training that no harm will come to the snake by having one layer of eye caps on the eyes.
The observant owner will notice this and take steps to improve husbandry techniques (specifically humidity levels) thereby allowing the eye caps to shed off properly during the next shed.
I feel that allowing the retained eye caps to shed naturally allows for a far less chance of harm to the snake's eyes from a novice snake keeper mucking about on the eyeball.
Just my thoughts on this.... no disrespect intended.