Low-tension (low-pressure) or normal-pressure glaucoma (glaucoma occurring with IOP < 21 mmHg) comprises about one third of all open-angle glaucomas in the United States and is even more common in Asia. Screening Screening for glaucoma can be done by primary physicians (more commonly an optometrist or ophthalmologist) by checking visual fields with frequency-doubling technology (FDT) perimetry and ophthalmoscopic evaluation of the optic nerve.