A visual acuity test is an exam that determines how well you can see the details of a word or symbol from a specific distance away. There are several different types of visual acuity test, most of which are very simple to carry out. Depending on the type of test and where it is conducted, the exam can be carried out by an optometrist, an ophthalmologist, an optician, a technician, or a nurse.
Visual acuity refers to the ability to discern the shapes and details of the things you see. It is just one factor in your overall vision, alongside color vision, peripheral vision, and depth perception.
There are no risks associated with visual acuity tests, and no special preparation is required.
A visual acuity test is one part of an overall eye examination. If you feel that you are experiencing a vision problem, or if your vision has changed, an eye exam may be necessary.
Visual acuity tests are frequently given to children, because early testing and detection can prevent vision problems from getting worse. Optometrists, driver’s license bureaus, and many other organizations also use this test to check your ability to see.
One widely used visual acuity test is the Snellen test. This test uses a chart of letters or symbols of different sizes, arranged in rows and columns. It uses the vision chart you are probably used to seeing in your school nurse’s office or doctor’s office. Viewed from a specific distance—usually 14 to 20 feet away—this chart can help determine how well you can see letters and shapes.
You will sit at a specific distance from the eye chart and will be asked to cover one eye with your hand or a piece of cardboard or plastic. You will be asked to read out loud the letters that you see with your uncovered eye. This process is then repeated with your other eye. Typically, you will be asked to read smaller and smaller letters until you can no longer accurately make those letters out.
Another frequently used visual acuity test is called “Random E’s.” This involves the patient identifying the direction that the letter “E” is facing. Looking at the letter on a chart or projection, the patient points either up, down, to the left, or to the right, depending on the direction that the letter is facing.
A visual acuity test administered at an eye clinic tends to be more sophisticated than the kind that a nurse might perform. During this test, you will look at the eye chart through a variety of different lenses. The chart might be projected or shown as a mirror reflection. The doctor will switch out the lenses you look through until you can see the chart clearly. This will help the doctor decide on your ideal eyeglass or contact lens prescription, if you need vision correction.
Visual acuity is expressed as a fraction, such as 20/20. Having 20/20 vision means that your visual acuity at 20 feet away from an object is normal. Alternatively, say, 20/40 vision means that you need to be 20 feet away to see an object that people can normally see from 40 feet away.
If your visual acuity is less than 20/20, your vision may need to be corrected with eyeglasses, contact lenses, or surgery. You might also have an eye condition, such as such as an eye infection or injury, which may need to be treated. You and your doctor will discuss your test results, as well as any treatment or correction that might be necessary.