The dominant eye can carry the team without even noticing. It is possible to have a nearly blind eye and not realize it until the good eye is covered. Acuity is always measured one eye at a time because it helps determine if one eye is seeing differently than the other. The letters are displayed with high contrast conditions – black letters on a white background. 20/15 and 20/10 are even more exceptional than the normal 20/20. The smaller the letters, the better the eyesight, and the lower the bottom number of the fraction.

The “big E” is usually 20/200 or 20/400 based on the digital system. The larger the letters, the worse the eyesight and the higher the bottom number of the fraction. The letters on the eye chart are calibrated to different sizes, which represent different levels of eyesight. Other countries measure vision in terms of meters, which makes 20/20 equivalent to 6/6. Most exam rooms use mirrors to achieve the 20 feet distance, as it is difficult to have exam rooms 20 feet long. The top number of the fraction represents the testing distance (ie. Results are written using Snellen fractions (20/20, 20/30, 20/40, etc). The Snellen eye chart is most commonly used to measure visual acuity. On the other hand, vision includes the ability to see colors, moving objects, peripheral vision, and depth perception.

Eyesight refers to visual acuity measured in terms of 20/_. The difference is not commonly acknowledged by the general public, but clinically speaking, there is a significant discrepancy. The 20/_ nomenclature is really a measurement of eyesight and not vision. While 20/20 is considered normal vision for healthy eyes, many people can see letters even smaller. “20/20 vision” is a unit of visual acuity (or clarity) measured at a specific distance.

So many people brag about his or her 20/20 vision, but what does that really mean? This is the year for optometrists and eye nerds around the world – 2020!

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