Know your Visual Acuity with Vision Tests

Checking your Vision Health

Gauging your visual abilities can be done through a series of vision tests.  Some employers may require this as part of a screening test of applicants that required excellent visual acuity such as pilots. Or it can be done to check the general health and functional abilities of the eyes in connection with a regular medical check-or in part when diagnosing eye or vision disorders. At the end of the day, the results will indicate your visual health in different areas and any deficiency can help point to an ophthalmologic or optometric solution.

Visual acuity tests

These are the most common vision exams designed to evaluate eyesight. They gauge the eye's ability to focus and perceive details at near and far distances. Each eye is tested and the tests involve recognizing letters or symbols of different sizes on an eye chart with and without corrective lenses. Several types of visual acuity tests may be used.

The Snellen test uses a wall chart with several rows of letters starting with the largest on top and the smallest at the bottom.  Devised by the National Eye Institute of the US National Institutes of Health, this chart is standard on all in EENT clinics.  Patients stand 20ft or 6m from the chart to read the smallest letters, covering one eye then another.  A correct reading with both eyes can register a 20/20 conclusion.  A counterpart E-chart containing only the letter E in various sizes and orientation is used for children who still could not read the alphabet.

Then there’s the Near Test which uses the Jaeger chart or small card containing a few lines of a paragraph in different text sizes to test how well you can read in near-field vision.  You are asked to read the smallest print you can read at 14 inches from your face.  This test is often administered for people from 40 years onwards since near vision declines with age.

Refraction test

This measures the eyes' refractive error which points to the need for corrective lenses. It is almost always done after a visual acuity test. Refractive errors can classify your visual focusing ability as being either nearsighted (you can focus better at details near you) or farsighted (you can focus better on objects afar). Patients are asked to peek through a retinoscope where a series of lenses are positioned one after another in front of your eyes against an object or chart and using light shone through it, is adjusted until the proper focus to your retina is established. You test one eye at a time and you state which lens gives you a better focus. Various lenses of differing dioptric values are positioned until you get which is best that complements your refraction ability.

Visual field tests

This is a series of tests to check for gaps in your side or peripheral vision. A complete visual field consists of the entire area seen whenever you are gazing in one direction. It is the field seen by both eyes concurrently and includes central visual field where the most detail is detected and the peripheral visual field. The test is often used to help confirm diagnosis in certain disorders in the eye or nervous system.  Any problem here will often limit your ability to clearly see objects that are supposed to be in your visual field or part of it. Several tests are involved.

  • The confirmation test gauges how well you can see events happening on the periphery while focusing on a central object,
  • The Amsker grid test checks on your central field of vision and is used to help confirm macular degeneration which causes you to lose vision in your center field, and
  • The Perimetry test requires you to peep into a perimeter bowl and lights flash randomly across your field of vision while staring at the center, You then press a button to confirm that you saw a flash each time. 
  • The tangent screen test makes use of a black screen with concentric white circles and lines leading out from the central bulls-eye point. Test objects of differing sizes are moved towards the center and you signal when you see the object.

Color Vision Test

This checks you ability to distinguish colors and is the standard in screening out people with color blindness which can disqualify certain job applicants for certain positions where color signaling is important, such as military personnel, commercial pilots, electronics staff, etc. The test involves deciphering dotted illustrations that distinguishes numbers or symbols  buried under different background colors. You won’t be able to pick out the object if you can’t see the color.