Generally speaking, as visually impaired is defined the person who is found with a visual reduction due to irreversible retinal damage (scotoma). The scotoma may affect only the central or the peripheral or be divided into many small scotomas. Patients with damage in the central part (e.g. aged related macular degeneration - ARMD) actually lose the ability to be autonomous in reading, writing and driving. Patients with peripheral damage have a restriction of the visual field "tubular vision" (eg in retinitis pigmentosa - RP), which prevents them from moving safely, so it becomes even difficult to walk alone. Patients with diffuse damage (e.g. in diabetic retinopathy - RD) are subject to drawbacks in all situations for the lack of some portions of the environment that surrounds them.

The ARMD, in particular, affects mainly older people, the statistics report that 3% of the population is a carrier of low vision and that over 85% of them has an ARMD. In addition, the elderly are subject to sclerosis of the lens (cataract), which invalidates further their vision. In these cases, cataract and macular degeneration, the simple removal of the opaque crystalline lens with implantation with an artificial lens (IOL-Intra Ocular Lens) do not always allow a functional advantage.