As part of human multisensorial interaction with the world, vision is often perceived as the dominant sensory modality. Eyes provide most of our information about the environment and efficient vision is considered to be vital to our overall health. Its loss has potentially greater effects on daily life than loss of limbs, memory, hearing or speech (1). The reduced independence associated with blindness, leading to social isolation, unemployment and depression, ranks it among the major health concerns, on a level with cancer and Alzheimer's (1). In addition to the personal impact of visual disability, the economic burden on health and social systems is significant (2). Retinal degenerative diseases caused by photoreceptor cell death are major causes of irreversible blindness in industrialized countries. Photoreceptor cell death leading eventually to impairment of central vision occurs in monogenic diseases such as retinitis pigmentosa, Stargardt disease, and Leber congenital amaurosis, as well as in complex age-related diseases such as age-related macular degeneration (AMD). For these blinding conditions, retinal Companion article to the Sackler Colloquium, "Using Monkey Models to Understand and Treat Human Brain Disorders," to be published in PNAS.