What do you feed your Oscars? Have we tested your water for ammonia/nitrite/nitrate? Cloudy eyes can often come about because of nutritional problems. They can also be caused by parasites. I would suggest that you trying to get some food that contains vitamins, or add vitamins to the food. I think you could try vitamin B (Riboflavin (B2)
http://www.anyvitamins.com/vitamin-b2-riboflavin-info.htm
You could also try vitamin C. as well have this can help with eye diseases. A good healthy balanced diet is the key to keeping fish healthy. Carry out extra water changes, I would do a water change every other day, around 20%. Whether it's parasites, I really don't know. I would try vitamins and a really good diet and extra tank maintenance and see what happens
