Mareks is a possibility due to the leg issues and the eyes too but so is mould. I had a coop of fully grown brahmas go down with the same problems you are describing and i was convinced it was Mareks but someone suggested i check the coop for mould and true enough I found a small amount about the size of a quarter on the underside of the feeder. just that tiny amount was enough to bring those big birds down. The treatment (apart from a thorough cleaning) was vitamin E capsules, selenium and charcoal. It was too late for some of them unfortunately but a few made a full recovery. It's worth a shot although in your case I still wouldn't rule Mareks out - poor chap sounds in a bad way. Best of luck.
