how old are they?
what all do you feed?
what do you use for bedding?
has the coop been cleaned recently?
could be ammonia fumes irritating the eyes..
are they exposed to a lot of dusts?
any lawn/garden/pesticide dusts used in their vicinity?
could the sand/salt spray/breezes be irritating their eyes?
could be something simple as "no sees" or other gnats irritating them..
describe the droppings..color and consistency.
check for other symptoms..such as wheezing or swollen eyes..
lack of appetite, acting depressed or lethargic..
some poultry vitamins and extra protein wouldn't hurt to boost their immune system..
maybe washing the eyes with saline eye wash, and trying some eye ointment..terramycin eye ointment is available at farm/feed/animal supply stores..
could be just keeping them washed will do..but the ointment might help protect them..
you can have a look at these products:
http://www.firststatevetsupply.com/store/index.php?cPath=21_57