5–16% combined (Bourne et Metformin al., 2013). In Australia specifically, a 2005 study

found age-related macular degeneration (48%), glaucoma (14%), cataract (12%) and diabetic retinopathy (11%) to be the most common causes of blindness, with neuro-ophthalmic conditions accounting for an additional 3% of cases (Taylor et al., 2005). There were an estimated 530,000 vision impaired people in Australia as of 2004, including 50,600 who were categorized as legally blind (visual acuity of ≤6/60). This figure is predicted to rise as a result of population ageing; Taylor et al., 2005 and Taylor et al., 2006 estimated that approximately 70,000 Australians would be legally blind by 2014, and almost 90,000 by 2024 (Taylor et al., 2005 and Taylor et al., 2006). Moreover, increasing rates of obesity-related Type II diabetes (Shaw et al., 2010) will undoubtedly contribute further to these figures. The direct health system costs in Australia for age-related macular degeneration, glaucoma and cataract alone were A$490 million in 2004. Indirect financial costs relating to lost income and carer costs for all visual impairment were estimated at A$3.2 billion, exclusive of transfer costs including lost tax revenue and the expenditure related to carer

and welfare payments, which were estimated at A$850 million (Taylor et al., 2006). Visual impairment has been associated with a 2.3 fold increase in mortality (McCarty et al., 2001) and the costs specific to loss of well-being due this website to the impact of disease and premature mortality have been estimated using daily adjusted life years (DALY) at A$4.8

billion (Taylor et al., 2006). While HSP90 not a major focus of this review, biological therapies represent a promising suite of existing and emerging therapeutic options for blindness caused by retinal disease. Gene replacement therapy (McClements and MacLaren, 2013 and Petrs-Silva and Linden, 2014), modulation of ocular autoimmune responses (Ambati et al., 2013, Buschini et al., 2011 and Rieck, 2013), transplantation of stem cells, photoreceptor precursor cells or bioengineered sheets of retinal tissue (Barber et al., 2013, Fernandez-Robredo et al., 2014 and Pearson, 2014) plus intraocular administration of neurotrophic, anti-angiogenic, intraocular pressure-lowering and antioxidant agents (Zarbin et al., 2013) are all techniques that are either currently in use, at clinical trial stage or being investigated in the laboratory. Among the rehabilitative options available to the blind, sensory substitution is a concept that has been explored extensively. Sensory substitution operates on the principle of replacing input from a lost sensory organ with an artificial sensor, with the output of that sensor redirected to the input of one or more remaining senses. A simple example of sensory substitution is the mobility cane, wherein a representation of the blind user׳s physical environment is obtained via a tactile method (Bach-y-Rita and Kercel, 2003).