a positive diagnosis is usually made when two of the following signs are present: elevated Iop, degeneration of the optic disc and visual field loss. Importantly, when abnormalities are identified at the optic disc a judgement has to be made as to whether or not the abnormalities are likely to represent progression of the condition (riordan-eva and Whitcher 2007). figures 2 and 3 compare a normal optic disc with a cupped, glaucomatous disc.