There is only one answer. Take the cat to the vet and do it quickly. If it is loosing its sight or getting catarracts you would never forgive yourself if something could have been done had it been discovered earlier. 11 isn't that old for a cat. Deuteronomy was over 18 when he died and Nehemeziah was 16. Don't even think about self diagnosis. Take the poor thing to the vet.