When testing Visual Acuity, the chart is placed a standardized distance away (usually 20 feet in the US), and the patient looks at the chart and reads aloud to the doctor or technician the smallest set of letters that they can see. It looks like this:Įach row of letters on the Snellen Eye Chart corresponds to a particular Visual Acuity value (ie: 20/20, 20/200, 20/15). Although there were others before him that created similar standards for Visual Acuity measurement, Dutch Ophthalmologist, Herman Snellen, who introduced his eponymous chart in 1862 and it has been the standard ever since. The international standard for Visual Acuity measurement is the Snellen Eye Chart. At 20/15, your vision is better than what is considered “normal,” and you see more than what a person with20/20 vision can see. With 20/15 vision, you will be able to stand 20 feet away from an object and correctly identify it, while the person with “normal” vision would have to stand 5 feet closer to that same object (15 feet away) to correctly identify it. On the flip side, let’s say that after LASIK your vision is 20/15 without glasses or contacts. So in this example, your vision is worse than “normal,” and you see less than what a person with 20/20 vision sees. That means you would have to stand 20 feet from an object (such as a street sign) to correctly identify it, while a person with “normal” vision could stand 200 feet away and correctly identify that same object. The bottom number also indicates how far away the “normal” vision person can be from that same object and still be able to correctly identify it. The top number represents how far away YOU are from an object while viewing it, while the bottom number represents the size of the letter or object that you are looking at. The top number is always 20, and the bottom number quantifies the clarity of the person’s vision compared to what is considered normal. In the US, Visual Acuity is represented by a fraction. We discuss presbyopia and how it relates to LASIK in another blog post here. Thanks to one of the many “gifts” that come with more birthdays, all eyes 45 or older manifest a condition called presbyopia, a person can have 20/20 vision for distance and still need glasses for near-range vision. One of the more common misunderstandings that some patients have is that 20/20 vision means no glasses at all. 20/20 is the standard Visual Acuity of “normal” vision, but a person can have vision that is better than or worse than “normal.” The specifics around a person’s quantity and quality of peripheral vision (how well someone sees off to the side without turning their eye) is outside the scope of this article. If a person has 20/20 vision, it means they see as much as a person should see when driving, reading a book or watching TV. So, Jack says that Jill “is 20/20.” What does that mean?Ģ0/20 vision is a measurement of central Visual Acuity, this is essentially the quantity of a person’s vision – how much they can see. Jack: “Do you need glasses or contacts, Jill?” When a person doesn’t need glasses or contacts to see, we say that that person “is 20/20,” right? For example: When we discuss the customized treatment with our patients, many times they ask questions like, “What does 20/20 actually mean?”, “What is the difference between quantity of vision and quality of vision?” In this article, we answer those questions and how they relate to LASIK at 20/20 Institute. This approach of utilizing only our most advanced treatment technology for every patient takes advantage of one of the most significant advancements in LASIK, Wavefront Optimized® LASIK, which is designed to improve both the patient’s probability of achieving a 20/20 or better visual result and to give the patient the best chances for quality night vision. When any patient visits 20/20 Institute for LASIK and is a good candidate, our LASIK Specialists customize a treatment plan designed to maximize each eye’s probability of safely achieving 20/20 or better vision. The majority of patients achieve better than 20/20 vision when they come to us for LASIK.
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