6ddd20e8_Common_diseases_of_goldfish__Treatment
[Disease and Causes] Cloudy eye Caused by poor water quality, poor diet, eye flukes, corneal damage, bacterial infection. [Symptoms] Entire surface or lens of eye takes on a cloudy, opaque appearance. There may be a build-up of mucus on the outer surface. [Reason for Infection] Most commonly caused by poor water conditions. A lack of vitamins in the diet may also cause clouding. On rare occasions digenetic flukes, such as Diplostomum, can cause problems. [Action] Improve water conditions. Use a good quality food containing added vitamins. [Treatment] 
Improving water conditions usually cures cloudy eyes. Eye flukes are uncommon and can be difficult to accurately diagnose and treat.
Common diseases of goldfish
Treatment