Snellen Chart

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The Snellen chart is displayed by selecting the Snellen icon on the Primary toolbar, pressing F2 on the keyboard of selecting Snellen on the remote control handset. The Snellen chart fully complies with the specifications of BS4724.



The letter / optotype combination displayed by default can be changed via the Snellen chart tab of the Options ... Chart Optotype Selection window as shown below. Pressing O on the secondary toolbar, keyboard or remote repeatedly will cycle through the five sets of default letters



To display the US progression of letter sizes tick the Use US Snellen chart check box.


You may also hide the 6/7.5 and 6/3 rows by tick the Hide 6/7.5 and Hide 6/3 check boxes respectively.


Test Chart 2016 provides a wide range of options for customizing the Snellen chart. These options may be selected using the Secondary toolbar or by using the keyboard or remote control.



These options are described under Test Charts - common features and include:


  • Row labels
  • Scrolling up and down
  • Randomising letters
  • Selecting different Optotypes
  • Displaying a Single Column
  • Displaying a Single Row
  • Crowded / Uncrowded
  • Duochrome split
  • Coloured chart
  • Low Contrast charts
  • Pointing and underlining


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    Turville Infinity balancing mode


    Turville (1946) published a monograph describing a binocular refraction procedure known as the Turville Infinity Balance (TIB). The technique involves viewing a Test Chart in a mirror and placing a septum on the mirror so that the patient sees the right side of the chart with the right eye and the left side of the chart with the left eye.  The border of the chart and the rest of the visual field is seen binocularly.


    As most of the field is seen binocularly, the patient will tend to adopt their normal binocular accommodative and oculomotor state so the test may be used for binocular balancing and checking for suppression and oculomotor imbalances.


    To select the TIB mode, select the T icon on the secondary toolbar or press T on the keyboard - there is no IR remote key for this option. This will display the chart shown below:



    Place a septum on the mirror in a position where one eye sees the letters on the right and the other eye sees the letters on the left.  The optimum width of the septum will depend on the viewing distances and the size of the screen and may require some experimentation.