It also helps to know if the eye is protruding or not, if it is inflamed, etc. A picture would really help. Generally, if a single eye is involved, I look towards physical trauma first, with or without secondary bacterial infection. In some cases, the skin fluke Neobenedenia will show up as just a single cloudy eye, but as the disease progresses, both eyes will be involved. Most generalized bacterial and protozoan disease, if cloudy eyes are a symptom, will involve both eyes more or less equally.
Jay