Ultraviolet radiation (UV) comes naturally from the sun. There are also some manmade lamps and tools (welding tools, for instance) that can produce UV radiation. For most of us, however, the sun is the...
The ability to see is dependent on the actions of several structures in and around the eyeball. The graphic below lists many of the essential components of the eye's optical system. When you look at an...
By looking at lots of people, eye doctors have decided what a "normal" human being should be able to see when standing 20 feet away from an eye chart. If you have 20/20 vision, it means that when you stand...