MEPS is a different beast than DoDMERB, but I can give you some general advice.
There are certain conditions which are "disqualifying" for enlistment. In actuality there are a lot of conditions; however, just because something is disqualifying does not mean it is the end of the road. The final adjudication for these issues for enlistment usually comes from personnel command (for the Navy this is BUPERS with advice from BUMED).
The place your son needs to go is to the recruiter that has been helping him. They will know how to submit waiver requests. Congressional requests likely aren't going to help.
Unfortunately a history of retinal hemorrhage means there was likely some serious eye trauma. This can potentially increase the chance that other eye problems will develop in the future even if it is "totally" healed. I can't say what the end result in your instance will be given there are many, many variables. Start with the recruiter. Best of luck.