After completion of baseline measures (IOP, visual fields, disc photos) and randomization, the subjects are followed for a minimum of 5 years with automated threshold central static perimetry (Humphrey program 30-2) twice yearly and stereoscopic optic disc photographs once yearly. Study end points are reproducible visual field loss and/or progressive optic disc damage in either eye of a patient attributed to glaucoma by a Masked Endpoint Committee. All visual fields and optic disc photographs are read in a masked fashion in Reading Centers.