The letter chart is usually placed at 6 metres which measures the far distance vision
( or at 3 metres with a mirror in place that increases the distance ) Patients will
be asked to read the letters.
There is a standard way of writing the results.
The results are measured in a fraction - but it is not too complicated. Eg 6/24
The upper part of the figure tells us at what distance the test was done at - which
is usually at 6 metres.
The lower part indicates the size of the letter - a smaller number here means a
For example, the larger letter on a Snellen Chart is usually the 6/60 letter, and
letters gradually decrease in size. A medium sized letter is 6/18. A tiny letter
size is 6/5
Good standard of vision is 6/6 - this is a small letter and is equivalent of twenty
The 20:20 vision term comes from measuring in feet rather than metres
The 6/4 letter is even smaller and indicates excellent vision.
If there is difficulty in seeing the smaller letters, the optician will do further
tests to determine if lenses will help to improve the vision ie if glasses or contact
lenses are needed to see better.
Different versions of the test chart
Other versions of the chart are available like Tumbling E or Landolt C . These have
the same shape but in different directions. So useful for people who are illiterate
or speak a different language.
eg in Landolt C chart, the broken circle has a gap, and this is put into different
positions on the chart. The person can say or point to which direction the gap is
seen. The size of each broken circle gets smaller further down the chart and so
can check the level of vision.
There are also charts in different languages like Arabic or Chinese.
The eye test charts measure visual acuity (level of vision) by having different sized
letters. These charts do vary in eye care practices - as they do not have the exact
same letters or sizes - and some charts may include very tiny letters.
A common one is called a Snellen Chart ( named after a Dutch eye doctor)