There are a number of commercially available treatments and preventatives. All fish are susceptible, especially the Silver Dollar and Piranha. It is fairly easy to diagnose and treat. White or gray material covering the eyes only. In the process, special attention should be made to assure that ammonia and nitrite levels stay within accepted measures.
Cataracts are fungal growths on the eyes.
Treatment with any aquarium fungicide should work. Its probability increases with water rich in ammonia or nitrates. Penicillin and tetracycline are among them. Corneybacteria causes swelling in the head which will push the eyes outward. Bulging sides and stomach.