What is 20/20 vision?

Often, when we think of 20/20 vision, thoughts of brain surgeons, nuclear physicists or rocket scientists spring to mind. However, 20/20 vision is not a measure of intellect or even ‘vision’ but rather of visual acuity.

Acuity is a component of vision, specifically how clear or sharp one’ s eyesight is. Measurement of visual acuity may be undertaken by a family doctor, local optometrist or ophthalmologist (eye specialist) as part of an overall assessment of vision. Good visual acuity, often described as 20/20 vision reflects optimal performance of the retina (particularly the fovea, a retinal region on which light is focused for central vision) and the brain (which interprets messages from the retina as the images we see).

20/20 vision as a measure of acuity is simply normal visual acuity when tested at a distance of 6 metres.

So, how is visual acuity measured?

Visual acuity is routinely measured by reading letters or images on a chart. The main type of chart used is called a ‘Snellen chart’, named after the Dutch ophthalmologist who devised this assessment. The chart is read at a standard distance of 6 metres and lines of letters of diminishing size are read.

The result of the test is documented as a fraction. The first number is the distance at which the chart is read and the secondary number the smallest letter size that is able to be read. Therefore normal visual acuity of 20/20 indicates that at 6 metres a person is able to read the 20’ line of letters, typical of normal sighted people.

Is 20/20 vision ‘perfect’ vision?

No. 20/20 vision is only normal vision, the average level of visual acuity you will find in a normal population. Remember many animals such as the birds of prey have much better sharpness of vision.

People can exceed the 20/20 rating on an acuity test if they are able to read the smaller letters below the 20’ line at 6 metres. Therefore an acuity score of 20/10 would indicate better than normal sharpness of vision.

How can I get 20/20 vision?

Anything that damages the fovea or affects the focusing of light on this key part of the retina will diminish visual acuity. A subnormal performance in visual acuity testing can be caused by, in particular, refractive error or retinal disease.
It is important to address any underlying causes of reduced visual acuity (such as diabetic retinopathy) with more thorough ophthalmic testing and prompt treatment or management.

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This article is not a substitute for a consultation with your surgeon. Before choosing to proceed with laser eye surgery your surgeon will have a detailed discussion with you about the right procedure and about the potential complications.

References

• https://www.aoa.org/patients-and-public/eye-and-vision-problems/glossary-of-eye-and-vision-conditions/visual-acuity
• https://en.wikipedia.org/wiki/Snellen_chart
• https://www.allaboutvision.com/eye-exam/2020-vision.htm
• https://www.ncbi.nlm.nih.gov/books/NBK215/