He has achromatopsia, with 20/200 vision. He can see enough to do many things. He can't drive and bright sunlight almost complete washes out his vision. He is pretty amazing with how little he let's it affect him from doing things well (he is a freshman in college now and doing very well). It's pretty cool to hear some of the examples here about sight limited folks doing solo skydives. He'll do some more tandems and then we'll explore some of the possibilities with a local DZ.
Achromatopsia is actually a pretty easy one to work around. That is more than enough vision to see a canopy overhead, larger landmarks on the ground (some DZs are better than others in this regard), probably enough for a larger print altimeter, assuming that he has already been fitted with contact lenses (if not, he definitely should be, as that works wonders with the associated nystagmus). Heck, in some states, he would be legal to drive with bioptic telescopes (do a google search on bioptic driving). As low vision goes, achromatopsia allows for great vision and really good function. I speak as a low vision doctor, rehab specialist, but lived for 10 years with a man with achromatopsia (my ex husband, who is the reason that I got into low vision to begin with). If you ever have questions, please feel free to PM me here.
I would feel very comfortable taking him up for an AFF jump. He really wouldn't need much other than an audible altimeter at the most to compensate for his vision. He could easily see hand signals, etc.