The glaucomas are a group of diseases characterised by progressive loss of retinal ganglion cells. This results in cupping of the optic disc, development of progressive and permanent visual field defects and potentially total blindness at the end stage of the disease. Glaucoma is currently the second commonest cause of blindness worldwide after cataracts (Resnikoff et al. 2004). Globally it is predicted to affect approximately 80 million people by 2020 (Quigley and Broman 2006).