You can try anti-biotics, and warm compresses.

It could be pink-eye. Which can spread to your entire colony.
It can also be caused by tooth abscesses. If you notice a lump in their jaw, that is likely the cause. Nothing can really be done about this, other than large amounts of expensive surgery.

If it's pink eye, it can be treated, but you'll want to quarantine the animals. It can spread.