If he does get the dragon scale eyes, you will notice scales slowly growing over his eyes. It takes a few months and you can train the fish to take food from a certain spot in the tank. Then if he becomes blind, you can keep feeding him in the same spot.
If he does become blind, keep the aquarium decorations in exactly the same spot and he will get around ok. If you change his decor around he will have trouble moving around.
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Fin rot is caused by poor water quality (generally ammonia) that damages the tissue on the tail and fins. This makes the ends look tatty and if it gets worse, it can become infected and you get red lines and red edging to the fins. If you keep ammonia and nitrite levels at 0ppm, and do regular water changes and gravel cleans, you should never see fin rot on the fish.
If a fish does get fin rot, check the water quality for pH, ammonia, nitrite and nitrate. Then do a massive water change and gravel clean each day for a week. Clean the filter too. Monitor for a few days and if it gets worse, add salt. if salt doesn't help, then you need antibiotics, but try cleaning the tank (daily water changes) first.