The Snellen tab of the Settings window includes the following panels

Snellen options

Options in this panel allow the various secondary formatting options for the Snellen chart to be enabled/disabled.  For example deselecting R will remove the option to Randomise letters and deselecting M will remove the option to show coloured charts. This allows a user to completely customise the functionality of the Snellen chart.

Snellen format options

Options in this panel allow the user to specify if a 6/120, 6/7.5 and 6/3 row are displayed on the Snellen chart), the default size (i.e. the current Snellen row after a reset) and the Default optotype (i.e the optotype set after a reset).


Snellen label options


Options in this panel allow the user to customise the labels shown on the left and right margins of the Snellen chart.


Snellen (m): The format favoured in the UK where VA is expressed as a function of a viewing distance of 6 metres.


Snellen (ft): The format favoured in the US where VA is expressed as a function of a  viewing distance of 20 feet.


Snellen decimal: The format favoured in much of Europe where VA is expressed as a Snellen decimal, e.g. 6/6=1, 6/12=0.5 etc.


Snellen: Snellen stands for the Log of the Minimum Angle of Resolution (MAR). The MAR is taken as the angle subtended by the gap between the limbs of a letter which is one fifth of the vertical angle subtended by the letter.


VAR (Visual Acuity Rating): The VAR score provides a much simpler method for scoring Snellen charts. The 0.00 (6/6) row is given a score of 100 and each letter has a score of 1.  


None:  No label is displayed.


The Font size of the labels can also be specified on this tab.  The optimum font size will depend on screen size and the distance that the practitioner views the chart from.