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What does 20/20 vision mean?

Laser eye surgery London

If you are looking for a laser eye clinic in London, then the London Vision Clinic should be on your shortlist.  

That may seem like a strong statement, but the London Vision Clinic emphasises that, in expert hands, laser eye surgery can be an extremely safe, life enhancing experience. More than 100,000 laser eye surgery procedures will be done in the UK this year. Read the guide to Laser Eye Surgery to help make the right choice for your eyesight.

Contact London Vision Clinic


Eye chart

In the most common visual acuity test, an optometrist places an eye chart at a standard distance(twenty feet or six metres, depending on the customary unit of measurement). At this distance, the symbols on the line representing “normal” acuity on the eye chart, designated 20/20, are the smallest line that a person with normal acuity can read at a distance of twenty feet.


It is possible to see better than the normal acuity level, expressed as a visual acuity of 20/16 or better. Three lines above the normal acuity line, the letters have twice the dimensions of those on the 20/20 line. The chart is at a distance of twenty feet, but a person with normal acuity can usually read these letters at a distance of forty feet. We call this line 20/40 (or 6/12). If this is the smallest line a person can read, the person’s acuity is “20/40,” meaning, that this person needs to approach to a distance of twenty feet to read letters that a person with normal acuity could read at forty feet.


A “legally blind” person cannot see the biggest letter on an eyechart (20/200) with glasses or contact lenses. Many people with refractive errors have the misconception that they have “bad vision” because they “can’t even read the E at the top of the chart without glasses.” However, in most situations where acuity ratios are mentioned, they refer to best corrected acuity. Many people with moderate myopia “cannot read the E” without glasses, but have no problem reading the 20/20 line or 20/15 lines with glasses.


In laser eye surgery, the surgeon’s goal is to get your vision without glasses after surgery to the same level as your best-corrected acuity (with glasses or contact lenses) before surgery, or better. When optometrists or surgeons say “gaining or losing a line of vision”, they mean the change in ability to read a line on the eye chart without glasses after surgery, from the ability to read the line with glasses before surgery.

Get a quote

Get a quote for laser eye treatment

If you are looking for a quote for laser eye surgery, or want more information about treatment in your local area, you can complete the Laser Eye Surgery Enquiry Form. Your enquiry will be forwarded to a maximum of three clinics or providers of laser eye treatment who partner with the Private Healthcare UK web site.