Are you aware of your own visual acuity?

Understanding visual acuity could enhance the way you perceive the world around you. Learn more about this simple eye test.

• Normal visual acuity is described as 20/20. It means that you are able to read letters of a particular size — usually the seventh line down on the Snellen chart — at a distance of six metres (20 feet).
• The result is shown as a fraction, and the higher the second number, the worse the vision.
• So if your result was 20/40, you would need letters twice as large as someone with normal vision in order to see them — or you'd need to be half the distance from the chart.
• Your optometrist may record your test results not as a Snellen fraction but as its corresponding number: 20/20 equals 1.0, while 20/40 equals 0.5 — so, when recorded as a decimal, the higher the number the better your vision.

• Visual acuity tends to improve up to the age of 25, and most young adults with healthy eyes can read the lines of smaller letters under the 20/20 row.
• This "better-than-normal" vision will score in the ranges indicated on the Snellen/Decimal chart.
• In fact the average score for healthy eyes is usually between 20/16 and 20/12, which means average vision is actually better than 20/20 or "normal."
• If your test result is 20/10 (or 6/3 or 2.0), it means that you can see letters six metres (20 feet) away that someone with "normal" eyesight could read from only three metres (10 feet).

• If you can't read the 20/20 line on the Snellen chart from the required distance, you have what's called "impaired visual acuity."
• You may be nearsighted, farsighted or have astigmatism, or you may have an eye disease such as cataracts or macular degeneration.
• If your acuity is only slightly reduced, to around 20/30, you can still drive safely.

• Your optometrist will also test how well you focus on things close-up, using a hand-held card with small chunks of text in progressively smaller print.
• You will be asked to hold the card at a set distance, usually about 40 centimetres (15 inches) from your eyes.
• Your optometrist will record the smallest text that you can read, and the distance at which you can do so.
• The letters on the card are calculated to show the equivalent of 20/20 vision and variations on either side (20/10, 20/40 and so on), with and without glasses or contact lenses.
• Most young people who score well for distant vision will also score 20/20 or better for near vision.
• But when we reach our forties, many of us notice that we need to hold the print farther and farther away in order to read it.
• This is known as presbyopia, and is nothing to worry about. All it means is that we need reading glasses.