Dutchman,
Sorry to hear about your friend's problems. I've been reading a bit bout this condition and info from this site states the cause of glaucoma:
The two main types of glaucoma are primary open angle glaucoma (POAG), and angle closure glaucoma. These are marked by an increase of intraocular pressure (IOP), or pressure inside the eye. When optic nerve damage has occurred despite a normal IOP, this is called normal tension glaucoma. Secondary glaucoma refers to any case in which another disease causes or contributes to increased eye pressure, resulting in optic nerve damage and vision loss.
I'm no doctor and you may want to post this on the medical board as diving will cause pressure around the eyes so I'm not sure how this will affect your friend.
For the part of getting a mask, these are wide field masks that you friend can try as fit is the most important thing in choosing a mask.
Cressi big eyes or matrix, Atomics ultraclear, mares xvision and pure vison, tusa viewtrek. Note these masks are twin lens masks and you can get prescription lenses installed.
SangP