White eye, illness or birth defect?

We just took this boy home today because he’d been sitting at the pet store for weeks, he’s got one white eye that he cannot see out of because he doesn’t respond to anything on that site

Does this seem like a severe case of cloudy eye, or just a defect? The first photo was very interesting to me because he flared at a light I held up and only one side of his gills flared.