What exactly was it doing that was abnormal? Was it scraping against rocks or the sand? Was it not eating? Was it hanging out near the top? Did it show any signs of disease (spots, white patches, rapid breathing, discoloration)?
In my limited experience with "eye issues" and based on what I've read, it is often due to less than optimal water conditions. Water changes and cleaning filters to get as much bacteria/"stuff" out of the water plus improved diet (add vitamins and make sure the fish is eating what it needs) usually clears things up. If it is the prelude to disease, then treating whatever it is usually clears it up.