Visiting your optician or optometrist for an eye prescription, you may find yourself immersed in a new and unfamiliar world. While your eye doctor will walk you through it and try to explain as much as possible, you may find that you need particular answers on certain eye questions that you encounter in your life. One of those questions may center on this whole concept of legal blindness. Whether or not you are legally blind can have an effect on a wide swath of things, ranging from your ability to obtain a driver’s license or obtain government disability benefits from the Social Security Administration. Because of this, it is important to understand whether your eye prescription is considered legally blind. With this knowledge in hand, you can jump through some of these procedural hoops and obtain some of the available benefits if you are legally blind.
Before talking about how your eye prescription tells you whether you are legally blind, it is critical to further explore what legal blindness actually is. To put it simply, legal blindness in the United States is measured by looking at your central visual acuity and your field of vision. Your central visual acuity is essentially what is in front of you. As you can guess, your field of vision is then what you see to the sides, above, and below you.
To test your vision, your optometrist or optician will make you look at a Snellen chart, which is the familiar chart of mixed letters that you read from a distance of about 20 feet. The overall goal of this eye test is to compare your vision to a historical norm. When completing this test, you are considered legally blind if your vision is deemed to be 20/200 or less. This means that if there is an object located approximately 200 feet away, you need to stand 20 feet away from it in order to see clearly. By contrast, a person with normal vision (i.e., 20/20 vision) can clearly see that object from 200 feet away. Your optometrist or optician may also give you a visual field test in order to test your field of vision. During that test, you may be considered legally blind if your peripheral vision is about 20 degrees or less.
Legal blindness means that your visual acuity is worse than 20/200 or a visual field that is less than 20 degrees even with the best possible correction. So once you visit your optician or optometrist and undergo these tests, you will want to take a look at your eye prescription. Simply put, if your prescription is -2.5 or lower, this means that you are legally blind. Visual acuity of -2.5 is equivalent to 20/200 vision. Visual acuity of -3.0, for instance, means that you have 20/250 or 20/300 vision. From there, visual acuity of -4.0 means that you have 20/400 vision. As we discussed above, having this sort of vision means that to see clearly, you need to be much closer to that certain object or person compared to the normal person in the population.
But where can you find this visual acuity number on your prescription? You will be looking at the first number for your left eye (labeled as “OS”) and right eye (labeled as “OD”). That first number represents diopters, which is the unit used to measure the correction of the lens that your eyes require. If you see that number as -2.5 or below, you, in all likelihood, are legally blind. That said, it is helpful to discuss this question further with your optician or optometrist. He or she will be able to further describe your prescription and the consequences of being legally blind.
Ultimately, if you are obtaining prescription eyewear, it is important to recognize whether or not you are legally blind. Having this knowledge will help you comply with certain laws and regulations (like driving standards) and help you take advantage of certain incentives for people with legal blindness. In sum, it is worth taking the time to learn more about your condition, whether you speak with your optometrist or do some in-depth independent research.
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