It’s a question our doctors get asked all the time: “What does 20/20 vision mean?” 20/20 refers to the smallest letter size that can be distinguished by a person with so-called “normal” vision. The letter chart associated with 20/20 vision was designed nearly 150 years ago, and while the term “20/20” is old, the system behind its designation is still used to describe patient’s vision today.
Our eye doctors can help you achieve 20/20 vision with great eye correction, and keep it there with regular eye check-ups.
At Vista Eye Care in Thornton, Colorado, our eye doctors use the letter chart to determine a patient’s entering visual acuity (what their vision is when they first arrive for their eye appointment), visual acuity with their glasses or contacts, visual acuity in the context of ocular disease such as cataracts, and visual acuity following refractive surgery such as LASIK or PRK. Visual acuity is the measurement of the overall image fineness that the eye can perceive. While having good visual acuity is important, there are other components of vision that reading a letter chart does not assess. For example, a patient may have color deficiency, high hyperopia, poor peripheral vision, poor focusing, poor depth perception, poor eye movement, or even poor eye health and still read 20/20 on the letter chart. Since many school screenings rely almost entirely on visual acuity (reading a letter chart) to assess eye functionality, the screenings commonly miss many diagnoses that could be better identified at an actual eye and vision exam.
A 20/20-sized letter is a letter that a person with “normal” vision can distinguish at a distance of 20 feet. A larger letter such as a 20/25 letter, can be distinguished by a person with 20/20 vision at 25 feet (because their vision is better than the person with 20/25 vision), though a person with 20/25 vision must view the letter at 20 feet (since their vision is not as good, they have to move 5 feet closer to see the letter). Confusing? It can be. Now, what about a person with 20/15 vision? That works the opposite way: a person with 20/15 vision can read a 20/20-sized letter at 20 feet, while someone with 20/20 vision (the poorer acuity in this case) must move up to 15 feet to see the letter.
Now, as our patients well know, our exam room are not 20 feet long, so how are we testing vision at 20 feet? The answer is that our cutting-edge computer-based visual acuity system is designed to produce digital letters that simulate the light seen if viewing it from 20 feet away. The nice thing about our visual acuity testing is that it allows us to switch between letters for adults, symbols for kids, and even movie clips for very young children. And unlike printed letter charts, Drs. Abert and Pedroza can mix the letters up in the middle of an exam to eliminate the chances of our patients memorizing the chart (not that you’d do that on purpose!).
After their yearly eye exam, our patients often ask “what is my vision, doc?” If they are a moderately nearsighted person, for example, they may have terrible distance vision without their glasses or contact lenses. 20/400 vision is not uncommon in an uncorrected patient’s eyes, and while that is certainly not “good” vision, that measurement really doesn’t tell us anything about the quality of their eyes. From a health perspective, we need to make sure that the vision is 20/20 (“normal”) when the eye’s refractive error (nearsightedness, farsightedness, presbyopia, or astigmatism) is corrected. A 20/400 eye can’t do much without glasses, though if an eye is not 20/20 with glasses, contact lenses, or after a refractive surgery such as LASIK, there must be a reason to explain why that vision is poor. Possible explanations are cataracts, glaucoma, diabetic retinopathy, amblyopia, or macular degeneration.
We recommend that all our patients be seen yearly for good eye health and vision. Call our Thornton, Colorado optometry office today to schedule exams for you and your family!