Normal vision is the ability to see comfortably what is around us, whether far away or near, with or without glasses. This simply means that the eye being tested is able to see an object at 20 feet as well as any eye with very good vision. As changes in vision become larger, most people experience more and more difficulty in their efforts to continue their usual visual activities, even with the best possible glasses or contact lenses . Low vision can occur at any age, but by far the greatest number of people who are partially sighted are the elderly.
Low vision is most often due to a change in central vision.
In a few cases it is associated with loss of colour vision or difficulty adapting to changes in brightness within the field of vision. A variety of disorders that affect the eye and the visual system may cause low vision. Birth defects, injuries, certain diseases of the body and aging all may lead to loss of sight. Loss of sight may also result from other conditions, such as cataract and glaucoma , or from damage to the optic nerve, which carries visual images to the brain. Since there are many diseases and conditions that can result in low vision, it is important to have a comprehensive eye examination by an ophthalmologist, a medically trained eye doctor.