Pop-eye is caused by a haemorrhage produced by gas in the capillaries of the eye socket, and can affect either one or both eyes.
The treatment would be to give a salt bath, as described for fungus, for a 36-hour period, and then carefully bathe the eyes with a 5 per cent answer of Argyrol which is a mild silver proteinate. An additional technique of treatment consists of a unique bath consisting of one drop of ammonia to every gallon of water.
The temperature of the bath should be increased to about 80° F and also the fish left in the answer for about 3 hours.
After this period, gradually decrease the ammonia content by adding new water until it is back to regular. The fish can then be returned to the original tank.