1. World Health Organization [Internet]. Visual Impairment and Blindness; [updated 2014 Aug; cited 2015 Sept 28]. http://www.who.int/mediacentre/factsheets/fs282/en
2. Causes and prevalence of visual impairment among adults in the United States;N Congdon;Archives of Ophthalmology,2004
3. National Eye Institute [Internet].Low Vision and Blindness Rehabilitation—National Plan for Eye and Vision Research [NEI Strategic Planning]; [updated 2004 cited 2016 March 12]. https://nei.nih.gov/strategicplanning/np_low
4. Association of visual impairment with mobility and physical function;ME Salive;Journal of the American Geriatrics Society,1994
5. Inventory of electronic mobility aids for persons with visual impairments: A literature review;UR Roentgen;Journal of Visual Impairment & Blindness,2008