LOW VISION

Low vision is a subspecialty within the professions of optometry and ophthalmology and Opticianry dealing with individuals who have less than normal vision even with the most accurate conventional prescription available. It can be a result of either congenital or acquired factors. An example of the former is Leber's congenital amaurosis and of the latter Age-Related Macular Degeneration.
See more at Wikipedia.org...

Vision /vi·sion/ 1. the sense by which objects in the external environment are perceived by means of the light they give off or reflect. 2. [more]Low vision - Community and Resources

significantly impaired vision which is not correctable with conventional devices.