LogMAR
The LogMAR tab of the Settings window includes the following panels:
LogMAR options
Options in this panel allow the various secondary formatting options for the LogMAR 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 LogMAR chart.
LogMAR format options
Options in this panel allow the user to specify the Minimum size (LogMAR) (i.e. the smallest LogMAR letters shown on the chart), the default size (i.e. the current LogMAR row after a reset) and the Default optotype (i.e the optotype set after a reset).
LogMAR label options
Options in this panel allow the user to customise the labels shown on the left and right margins of the LogMAR 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.
LogMAR: LogMAR 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 logMAR charts. The 0.00 (6/6) row is given a score of 100 and each letter has a score of 1.
No. Letters : Some clinics have adopted a methodology where the number of letters read by the patient from a starting LogMAR row is recorded (usually the top row on a fixed back-illuminated chart). Unfortunately the starting LogMAR row used is not standardised resulting in differences between clinics. The Thomson Test Chart allows the user to specify the starting LogMAR row to provide continuity with an existing scoring system.
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.
