Do the eyelids roll in? Sometimes if the eyelashes rub the eyes, it causes irritation and sores, causing tears and crusting of eyes.
Alternatively an eye infection such as New forest eye could be causing crusting.
If the eyes are irritated by anything, it can be very serious as eyes have a very thin surface before they rupture, so if in any doubt, prompt, aggressive treatment for the condition at hand is necessary.
I think it would be worth a trip to the vet with it if you're not sure what it is.