Ornate box turtle help

I keep Ornate box turtles. They live year round outside, and generally seem to thrive (eat well, mate, lay eggs, etc). While most of them do well/fine, i periodically get 1 or 2 whose eyes become almost glued shut. The eyes are not puffy, just shut and will not open. The afflicted turtles do not appear to have any upper repository problems (no mouth breathing, no bubbles from nose, etc.) but none they can't or won't open their eyes. They can not see to eat. One has a white film over it's eyes as if it;s wearing a white contact lens. I have seen this before and eventually the turtle wiped it away. Any suggestions for what may be causing this and remedies? Again, most of the turtles seem fine/do fine, but it's 1 or 2 that get this shut eye thing. Any suggestions from experienced keepers would be most welcome. Thanks!