Visual acuity measures our ability to see small detailed black objects on a white background, such as printed text.
What does 20/20 or 6/6 mean?
20/20 and 6/6 (6/6 is the metric measure) only indicate how sharp or clear your vision is at a distance. Overall vision also includes peripheral awareness or side, eye coordination, depth perception, focusing ability and color vision.
20/20 or 6/6 vision describes normal visual clarity or sharpness measured at a distance of 20 feet, or 6 metres, from an object. If you have 6/6 vision, you can see clearly at 6 metres what should normally be seen at that distance. If you have 6/30 (20/100) vision, it means that you must be as close as 6 metres (20 feet) to see what a person with normal vision can see at 30 metres (100 feet)
Why do some people have less than 20/20 or 6/6 vision?
The ability to see objects clearly is affected by many factors. Eye conditions like nearsightedness, farsightedness or astigmatism or eye diseases influence visual acuity.
Ishihara test for colour Blindness
Color blindness is an inaccurate term for a lack of perceptual sensitivity to certain colors. Absolute color blindness is almost unknown. There are three types of color receptors in our eyes, red, green and blue. We also have black and white receptors. They are more sensitive than the color receptors, that is why we have poor color perception in the dark.