Quite some time ago, one of my Chromis began acting in the same manner. He was always bumping into things and became much more reclusive as a result. He would hang out at the bottom of the tank and actually learnt to feel his way around with his fins. It took a while for me to figure out what was going on, and at one point I thought he was guarding eggs because of this very reclusive behaviour in a rocky back-corner of the tank. He would still find food and eat actively (nowhere near as successfully as in the past, though) but his feeding seemed to be more a process of sniffing it out in the water and randomly snapping in the general area of food, rather than seeing and chasing it.
I researched quite a bit for similar experiences, and from what I learnt, it isn't that uncommon for an older Chromis to show this sort of behaviour. It may just be what happens when some of them reach old age. Mine also developed dropsy and, although I was able to reverse the swelling and keep him healthy with spot feedings for quite some time, he inevitably passed away.
The best advice I can offer from my own experience would be to keep your parameters as close to optimal as you can, and to take the time to spot feed your Chromis to ensure he is getting a proper diet. I would also advise against moving him to another tank (eg: hospital tank for any kind of treatment or isolated feeding regime) because, if he has become blind, the familiarity he has in his current tank will help keep him more relaxed and have a better chance to keep healthy.
Hope this helps.
