Being blind, is just simply the condition of not having visual perception. Like everything medical, and even today non-medical there is a more 'advanced' definition of blindness. This definition in North America is defined as having 20/200 or less in an individual's best eye after eye correction, such as contact lenses, or glasses. 20/200 means that you would stand 20 ft away from an object and see the same thing as someone with normal eyesight would see from 200ft.
Distance is one of the major factors in determining blindness, with the second being the visual field. A normal person has a visual field of 180 degrees, with someone who is blind having merely 20 degrees. Alot of times we assume that when someone is legally blind that they cannot see anything at all. This assumption holds true in ten percent of cases, with the rest having some vision. Even just some light perception accounts for vision.
One of the leading causes of blindness is Diseases. The most common causes of blindness around the world as determined by WHO (World Health Organization) are:
- cataracts (47.8%)
- glaucoma (12.3%)
- age-related macular degeneration (AMD) (8.7%)
- corneal opacity (5.1%)
- diabetic retinopathy (4.8%)
- trachoma (3.6%)
Developing countries are greatly more prone to developing visual impairment as it is one of the consequences of treatable or preventable conditions, that they simply just cannot afford.