Rapid and accurate detection of glaucomatous damage at its onset or on its progression is desirable for optimum patient management. Tonometry alone is insufficient in ensuring adequacy of therapy; also required are stereoscopic optic disc review and quantitative perimetry. Signs of early optic nerve head damage from primary open angle glaucoma (POAG) include nerve fibre layer haemorrhage, a generalised increase in optic cup size and a localised increase in optic cup size. The latter two are absolute indications for initiation or acceleration of ocular hypotensive therapy. Accurate perimetric plotting of the normal blind spot, careful examination for a nasal step, and a thorough search of the paracentral area of the visual field are recommended for detection of the earliest visual field changes in POAG. Paracentral scotomata, nasal steps and repeated asymmetric concentric contraction of the isopters are three early, specific signs of nerve fibre bundle damage.