Visual impairment is an umbrella term for low vision and legal blindness. There are a number of terms that are often thrown about haphazardly — such as “legally blind,” “visually impaired” and “low vision” — that many people may assume mean the same thing, but actually refer to very different, very specific optical conditions. A diagnosis of one of these conditions versus another may merit a different type of treatment to help correct the problem. Additionally, some treatment options may also be limited based on the exact medical condition diagnosed by a professional. Visual acuity, or the clearness of vision, is used in part to determine the appropriate diagnosis and level of visual performance.
William Smith, OD, optometrist at the UPMC Eye Center, explains, “Visual acuity tests are used to evaluate your eyesight and their ability to see near and far distances. The most common test is a letter chart with rows of letters that decrease in size from top to bottle. We ask patients to read the chart using both eyes and with each eye individually. The results of the test are given as a fraction, for example 20/20.”
Having 20/20 vision means that at 20 feet away from an object your vision is normal. 20/40 vision means that you would need to stand 20 feet away from an object that a person with normal vision could see at 40 feet.
Low vision can be a loss of visual acuity that interferes with daily activities and is related to an eye disease. This is not complete blindness; a person in this category can have a range of visual acuity of usually 20/70 and worse. Previously, low vision was referred to as partial sight or partial blindness.
Legal blindness refers to people whose best corrected visual acuity is less than 20/200 in their better seeing eye. People who are legally blind can also have a limited field of vision, peripheral vision, which is less than 20 degrees at its widest point. This is also known as tunnel vision.
Individuals who fall into these categories are those whose vision is unable to be improved through the use of conventional eyeglasses, contact lenses, surgeries or medications. If you have poor vision, but it corrects to 20/20 with use of a conventional eyeglasses or contact lenses, you cannot be considered legally blind.
Dr. Will recommends having your vision regularly checked. He says, “We recommend having an exam at least every two years, however, please contact your eye doctor anytime you notice changes in your vision.”
The UPMC Eye Center also offers low vision services to help people with visual impairment make the most of their remaining vision to improve activities of daily living and enhance overall quality of life.
To learn more about the latest development in the field of eye care or to make an appointment with an expert, please visit the UPMC Eye Center website or call 412-647-2200.