I found this on Fishchannel.com
Several things can cause cloudy eyes in aquarium fish. Internal parasites, such as protozoa or flukes, are one cause. Another is the onset of cataracts in fish. I'm not aware of any treatments for those problems. Bacteria can infect fish eyes damaged by injury. Treatment with a good antibiotic should cure these infections. Dietary deficiencies, such as lack of vitamin A, may contribute to poor fish eye health.
The most common cause of cloudy eyes in aquarium fish seems to be poor water quality, especially when the pH drops too low. In my years as an aquarium dealer, I ran many water tests for customers. When they complained of aquarium fish with cloudy eyes, almost without exception I found the pH in their aquariums to be extremely low. Often, the pH was so low it tested off the chart.
