Visual impairment affects mobility and orientation, and development in the social, emotional, language and cognitive areas. These influence the student's functioning and learning potential. There are developmental implications for visual impairment at different ages. This chapter presents some types of visual impairment, such as refractive errors, cataract, nystagmus and retinitis pigmentosa. Cerebral (cortical) visual impairment is distinguished from ocular visual impairment in which parts of the eye are affected leading to difficulties with visual acuity, field of vision, colour vision and adaptability to light. Factors affecting foetal development that can cause visual impairment include maternal rubella. This can lead to a baby having visual impairment such as cataracts, where cloudiness of the eye lens leads to a loss of vision for detail. A specialist teacher for the visually impaired may work directly or as an advisor in various settings. Services may include visiting and working in mainstream and special schools, training and consultancy, and joint work with families and schools.