Get an API liquid test kit and post here the results of ammonia, nitrite, nitrate and pH.
How are the gills?
What were the past eye issues? Cataracts? Blindness?
Pics of the eyes?
Are you sure you have no sharp decors that could injure them?
Prior to their deaths, what other symptoms were observed?
How old are these?
Admittedly, sunken eyes are rare but not unheard of. A few cases I've seen were from goldfish, mostly telescopes. I wonder if something is causing the fluids in their eyes to drain off thus resulting in this. Old age usually causes this and even injuries.
How are the gills?
What were the past eye issues? Cataracts? Blindness?
Pics of the eyes?
Are you sure you have no sharp decors that could injure them?
Prior to their deaths, what other symptoms were observed?
How old are these?
Admittedly, sunken eyes are rare but not unheard of. A few cases I've seen were from goldfish, mostly telescopes. I wonder if something is causing the fluids in their eyes to drain off thus resulting in this. Old age usually causes this and even injuries.

