I seem to notice the problem occur more when it is dry. Actualy, here, that is this time of year more than not, because all the humidity "freezes" out of the air and the hay gets very dry. I have taken to putting a drop or two of eyedrops (Murine, Visine, etc.) in every eye that is not open or has any "goopy" substance in the corner on my "10-day" check. This has seemed to prevent any problems, and is much easier than worrying about an eye that is "gooped" shut a couple of days later.