I have eye issues with lots of my babies, usually between 3-5 weeks. I just leave them they suaully improve in a few days and it doesnt occur again. Id an adult had the same problem or reoccuring eye infection then I would be concerned.
well after our baby had it my daughter found a website that said "sticky eyes" are more common in astrex babies and it happens around the time their eyes open they called it nest box eye, it is not an infection and clears up with bathing.......this is what happened to ours. but it only happened to one baby.its eyes finally opened propley 3-4 days after the others and I put it down to it being the smallest. she is just fine now.... oh and she is not astrex either. I just wondered why it happens to some and why her eyes were slow opening.
I have observed the differences in when the babies open their eyes and have found that in general larger babies open thier eyes earlier while runts (or smallest in the litter as I dont generally keep any proper runts) can often be several days later in opening their eyes. Its a general rule though and some cases just dont follow it, recently one of the smaller babies in my litter of blues opened his eyes at 10 days old the others didnt until day 13, and they all opened theirs on the same day.
I use hay for my mice to nest in, they live in the garage so they need the extra warmth that hay gives them, shredded papr works too but I find it gets damp quickly from the condensation. Anyway I think using hay can lead to some eye issues, either the particles of dust getting in there or simply being poked in the eye by a sharp bit. But as I said mine all clear up in a few days, I dont think its uncommon.