Cloudy eyes on Balas

Well, getting ready to take our vacation later this week, and notice that
all my Bala's are starting to get cloudy eyes.

The largest bala, about 6", the soft tissue around the center of the eye is
sunken in, and the eye is a dull brown/off white, his other eye is just
offwhite. The three other balas ranging from 4"-5" have a small white spot
in the middle of one eye.

So, what causes this? Tank perams are normal for me, nothing has changed in
the last 6 months. Filtration is good, water is crystal clear, no odors.

How seriuos is this and what do I do to treat them?

Info on the web is vague, mixed opinions.

Thanks