Conditions that impact the ability to see can be caused by injury, by lesions of the brain or optic nerve, by disease of the cornea or retina, by pathological changes originating in systemic disorders and by cataract, glaucoma, or retinal detachment. Blindness can be caused by infectious diseases and by dietary deficiencies in underdeveloped countries. More people than ever are facing the threat of blindness from age-related eye disease. Over one million Americans aged 40 and over are currently blind and an additional 2.4 million are visually impaired. These numbers are expected to double over the next 30 years as the Baby Boomer generation ages. The leading causes of vision impairment and blindness in the U.S. include: diabetic retinopathy, age-related macular degeneration (the most common cause of blindness and vision impairment in Americans over age 60), cataract (the leading cause of blindness in the world), and glaucoma.