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Reviewed March 16, 2014
What You'll Get
- $39 for $175 worth of eyewear<p>
20/20 Vision: An Imperfect Ratio
The goal of wearing glasses, or contact lenses, is often to achieve that magic mark of 20/20 vision. Read on to find out what this metric really means.
Possessing 20/20 vision may be considered perfect, a level of visual acuity reserved for Navy pilots and the bald eagles that train them, but in fact it's not even close to average. Developed by Dutch optometrist Hermann Snellen in the 1860s, the 20/20 standard is a somewhat arbitrary distinction. After inventing his now-iconic eye chart—which consists of lines of standardized letters that get progressively smaller—Snellen also instituted the concept of a ratio to define the clarity of a patient's vision. The denominator represents how many feet away a person of normal visual acuity could stand while still discerning the letters with the same level of clarity as the patient. In other words, 20/40 vision means the patient needs to stand 20 feet away to make out the same size letters as a person with standard vision can from 40 feet.
Because the 20/20 standard is arbitrary, many people actually have considerably better eyesight, represented by such ratios as 20/15 or 20/10. In fact, in the United States, the average visual acuity is sharper than 20/20 until about age 60 or 70, when people's vision naturally starts to decline as their bangs finally grow past their eyes. Also, though it's useful for determining basic shortcomings of vision, an eye chart can't diagnose a proper glasses or contact prescription. To determine that, optometrists test many other factors, including depth perception, peripheral vision, x-ray vision, and focusing skills.
The Fine Print
Promotional value expires 90 days after purchase. Amount paid never expires. Limit 1 per person, may buy 1 additional as a gift. Limit 1 per visit. In-store only. Not valid for sale items. Must purchase frames and lenses. Not valid on lenses only for frames only. Merchant is solely responsible to purchasers for the care and quality of the advertised goods and services.