There are a number of different eye diseases which can arrise in fish.

Commonly, a cloudiness either of one eye or both, can arrise often associated with moving the fish or aggression between fish. The cloudiness is a bacterial infection which comes opportunistically when the cornea is damaged traumatically. When it's on one eye and follows a shape it's most likely from a scratch possibly sustained in handling or when fish are added to a new tank and getting chased. When it's both eyes the cause is usually a general external bacterial infection, commonly a vibrio or pseudomonas bacteria species infection. The good news is that any of the antibiotics commonly available (oxytetracycline, tmp sulfa, nitrofurazone) will work in any of the modes of treatment( food,bath, etc.). Often the unilateral slight cloudiness will resolve on it's own after the fish is acclimated or aggression is sorted out between the fish or you seperate the fish.

Popeye is a common name for exophthalmous. It when fluid or gas builds behind the fishes eye or within the eyeball itself and causes it to bulge out. One sided versus bilateral and fluid vs gas gives a clue as to what might be the cause. One sided and with gas inside the eye is usually from a scratch or another trauma. Both sides and fluid is more often a systemic diseases and may not be an infection. Gas usually means a bacterial infection if within the eye but if it's behind the eye it could just be gas from the blood being deposited in the wrong place ( the highly vascular eye and a metabolic acidisosis from fish stress which causes gas to be dropped by the blood in the space behind the eye). You can relieve pressure by using a tuberculin syringe(from walgreens) if you can see the gas pocket, or just aim way back (need to get behind the eyeball). After that, if it was stress related or something metabolic (maybe even stuff like liver or kidney failure) you will probably never know. The best most folks can do is shotgun an antibiotic food or bath treatment. I like the aminoglycosides (kanacyn and neocyn by seachem) hwowever for the bilateral fluid cases, I often have found that when other shotgunned antibiotics didn;t work, erythromycin resolved the popped eyes(works on more gram positive bacteria and is specifically prescribed for salmon with a certain bacterial kidney infection).