It really is very important that you either test your water on a regular basis by going to a fish store, or get yourself some test kits. It doesn't matter what forum you go on, if you ask for help regarding problems in your tank, we are going to ask for your water readings. Without knowing this information, it is virtually impossible to give you accurate advice. I apologise if it sounds like I'm lecturing you, if it is so important that you have some idea of what your water conditions are. You don't need to test it every day, if your fish don't show signs of ill health, you only need to do it every now and then.
Now regarding your Oscars condition. Oscars have got excellent eyesight so even with one eye, you will know whether your Oscar can see food. Animals can cope perfectly okay but just one eye, so as long as the other eye is okay, it shouldn't have a problem feeding. If the eye looks like it's damaged, I suspect there isn't much you can do about it. What we've got to try and determine is whether this has happened due to poor water conditions, or maybe an injury. If it was down to poor water conditions, I think both sides would probably be affected. Poor water conditions normally cause the eyes to go cloudy.
If you can get your water tested somewhere, please do tell us what the results are.