just wondering if the aviary is maybe too open?....
if so maybe worth sheltering it slightly, i say this, as i , at one time, kept some hens in an open aviary, and had something like this,, it wasnt one eyed cold as there were no bubbles on the bottom eyelid,, i sheltered part of the aviary [where they roosted] and used pharma belge de weerd eye drops [yes weerd ;D ;D]
simply really eye drops as mentioned b4 in this thread
this one says on the bottle ;D disinfection of the eyes, mucouis membranes, the lacrymal canal, and the mucious membranes of the nose, in cases of swollen and wet eyes,, inflamed third eyelid [we used to call this third eyelid the nicky membrane],,but this bottle seemed to do the trick along with some shelter,,,,,but this aviary was completely wide open to the elements ,,,,
another cheaper remedy ;D was to spit on to the birds eye [must be from a non smoker or drinker ;D, as clean spit contains an anti biotic , that can be of help.
another remedy was golden eye ointment simply from the chemist,, dont know if you can still get this now, good luck