Snellen Eye Chart


The eye test measurment developed in 1862 by Mr Snellen. The chart measures how well you can see at various levels of correction with glasses.

Snellen Eye ChartThere are a number of different Snellen charts available for use, the most common being the chart that is read from 6 metres away. The chart comprises of 11 rows of letters, starting from the top with the largest. Moving down the chart the letters become smaller, allowing the optician to accurately determine the patients visual acuity. This is possible by asking the patient to read down the lines until they can no longer read any more letters. The visual acuity score can then be calculated.

The standard visual acuity of the population is taken as being 6/6 or so called ‘20 20’ vision. This means that for a normal person, they should be able to read the line labelled 6 on the Snellen chart at a distance of 6 metes, hence 6/6. As visual acuity decreases, so does the line read, becoming 5/6, 4/6 etc. This enables opticians to accurately measure and correct poor eyesight.


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