What allergy medicine can glaucoma patients use.

All if open angle. Ppatients with open angle glaucoma can use all allergy medication. Allergy medications can rarely precipitate angle closure in patients with narrow or occludable angles. Ask you ophthalmologist whether you have open angles.
Depends on type . Most topical( eye drop) antihistamines are acceptable, like zaditor, (ketotifen) Claritin & zrytec eye drops. With oral agents, it depends on the type of glaucoma you have. In narrow angle or closed angle glaucoma, extreme caution is advisable. I'd recommend a gonioscopy and a provocative test by your eye md to assess whether you have iop raising potential, then have iridotomy.