The eye is the most significant and precious part of our body. As much as 70-80% of what we perceive and learn is achieved through vision. Being able to see clearly is therefore the most important factor that influences our capacity to enjoy a normal life. Clear vision is the result of light being focused by the cornea and the crystalline lens onto the retina. If the eye's curvature, or focusing power, does not correspond with its length, the retina will not receive a clear, focused image, causing a condition called Refractive Error or Ametropia. Refractive errors are measured in units of dioptric powers (Diopters or D):
According to the American Optometry Association, 20/20 vision is a term used to express normal visual acuity (the clarity or sharpness of vision) measured at a distance of 20 feet. If you have 20/20 vision, you can see clearly at 20 feet what should normally be seen at that distance. If you have 20/40 vision, it means that you must be as close as 20 feet to see what a person with 20/20 vision can see from 40 feet.
20/20 does not necessarily mean perfect vision. 20/20 vision only indicates the sharpness or clarity of vision at a distance. There are other important vision skills, including peripheral awareness or side vision, eye coordination, depth perception, focusing ability and color vision that contribute to your overall visual ability.