What size tank is he in? Are there any more fish in the tank with him? Have you checked your water chemistry?
Ammonia, nitrite, ph, and Nitrate levels? A fish sitting on the bottom isn't normal.
Your water chemistry may be off kilter. If you do not have a test kit then please take a sample in to the pet store and have them test it for you. I don't think there is anything wrong with his eyesite he sounds like he is refusing to eat which is bad. He could be constipated. Try feeding him, dried worms, or frozen peas that have been slightly thawed and popped out of their skin and slightly mushed. You might want to change 30% of the water in the tank and add 1 Tbs of aquarium salt per 5 gallons of water. You can also add Melafix which is a good fish tonic...all natural.
Keep us posted and good luck!