About 80% of blind people have residual vision. It can be difficult to understand how a person with a particular eye condition can see some things while not seeing others. While some people lose a lot of vision in a short time, others slowly lose vision. Many diseases that cause blindness begin to affect a certain part of vision and then progress to remove more vision. For example, macular degeneration initially affects a person`s central vision (the vision that makes us see straight ahead). Visual examples of what individuals might see if they have diseases such as macular degeneration, glaucoma, cataracts, diabetic retinopathy, and retinitis pigmentosa can be found on the National Eye Institute`s website at www.nei.nih.gov. Legal blindness can also be caused by glaucoma, a disease in which retinal neurons that send signal from the eye to the brain die. This disease usually progresses slowly over time, with patients losing some of their visual field and/or visual acuity. If the field of vision decreases to 20 degrees or less, the patient is legally blind. The normal binocular field of view (with both eyes) in the horizontal plane is about 180 degrees. The progression of visual field loss can usually be slowed or stopped by lowering eye pressure with medication and/or surgery. The sooner you are diagnosed and treated, the better you will preserve your vision.

But where can you find that visual acuity number on your prescription? You will look at the first number for your left eye (labeled as “OS”) and the right eye (labeled “OD”). This first number represents diopters, which are the unit used to measure the lens correction your eyes need. If you see this number as -2.5 or less, you are probably legally blind. However, it is helpful to discuss this issue further with your optician or optician. He or she will be able to describe your prescription and the consequences of legal blindness in more detail. Did you know: The largest letter on the diagram (an E on most Snellen diagrams) is a 20/200 vision. If someone cannot distinguish this letter with his prescribed glasses, he is considered blind within the meaning of the law. Legal blindness includes total blindness, but not all people who are legally blind are completely blind. Many blind people, for example, can see shapes and colors.

Methods: A community-based retrospective longitudinal study of residents of Olmsted County, Minnesota, newly diagnosed with open-angle glaucoma between 1965 and 1980 and followed until 1998. A case-control study was conducted in which patients who progressed to legal blindness by glaucoma were compared to patients with age and visual field adjustment who did not progress to blindness. Striem-Amit E, Guendelman M, Amedi A. “Visual acuity” of congenital blind people by visual sensory substitution for auditory. PLoS One. 2012;7(3):e33136. doi:10.1371/journal.pone.0033136 If a visual impairment reduces visual acuity to 20/200 or one-tenth of normal vision — which is 20/20 even with glasses or contact lenses — a person in North America is considered legally blind. Ultimately, when you get prescription glasses, it`s important to know if you`re legally blind. With this knowledge, you can comply with certain laws and regulations (such as standards of conduct) and take advantage of certain incentives for people with legal blindness. In summary, it`s worth taking the time to learn more about your condition, whether you`re talking to your optician or doing extensive independent research.

To test your eyesight, your optician or optometrist will encourage you to look at a map of Snellen, which is the familiar board of mixed letters that you read from a distance of about 20 feet. The overall goal of this vision test is to compare your vision to a historical norm. If you take this test, you will be considered legally blind if your vision is rated 20/200 or less. This means that if an object is about 200 feet away, you need to stand 20 feet away from it to see clearly. In contrast, a person with normal vision (i.e., 20/20 vision) can clearly see this object from 200 feet away. Your optometrist or optometrist may also give you a visual field test to test your field of vision. During this test, you may be considered legally blind if your peripheral vision is about 20 degrees or less. There are assistive technologies available to improve the vision of people who are legally blind. For example, eSight is an eyeglass device that can greatly improve vision and improve quality of life.

Fifty-six out of 290 patients developed blindness in at least one eye during the 34-year study period. Most people who progressed to blindness had moderate to advanced visual field loss at the time of glaucoma diagnosis. Those who became legally blind had lower or similar mean intraocular pressure (IOP) at treatment than patients who did not become blind, although IOP variability was higher in the blind group. Different IOP sensitivities were shown, as some eyes with initially normal discs and visual fields became blind to 20mm IOP, while others did not deteriorate. Changes in medical treatment after progression of visual field damage were less effective in lowering intraocular pressure in the blind group than in the non-blind group. People often ask about the difference between being blind and being “legally blind.” Because “blindness” can mean many different things, legal blindness is the threshold at which a person is considered visually impaired for legal purposes, such as for insurance purposes, to receive certain benefits, or to enroll in various programs.