The best treatment for cloudy eyes is big daily water changes and gravel cleans for at least one week.
You can add rock salt to tanks with Corydoras and tetras at a dose rate of 1 to 2 heaped tablespoons of salt per 20 litres (5 gallons). Keep salt in tank for at least 1 week.
If you do water changes while using salt, add salt to the new water before adding it to the tank so the salinity (salt level) remains stable.