Before using a device, it must be calibrated to ensure that the tests/stimuli are correctly scaled and the colours adjusted appropriately.


To calibrate a device, select the device from the list and select Calibrate as shown below:



Calibrate Size


The calibration screen will be displayed on the device.  Use a ruler to measure the height of the Z and the width of the horizontal line ON THE DEVICE.  Enter these measurements in mm on the Thomson Near Chart app.


Also enter the default viewing distance for Distance and Near in cm.  These viewing distances will be used to scale the stimuli where measurements are related to the angle subtended by the letter/stimulus.


Calibrate Dissociation Colours


Some of the binocular vision tests require the patient to wear red/green glasses in order to dissociate the eyes.  It is important that the colours displayed on the device are well matched to the spectral characteristics of the red/green glasses.


To check this select the Calibrate Dissociation Colours tab as shown below:



By default, a cyan and red bar will be shown on the device.  Look at the device screen through the RED LENS ONLY


The aim is for the Red bar to disappear against the grey background and for the Cyan bar to look black as shown below:



Now look at the device screen through the GREEN LENS ONLY


The aim is for the Cyan bar to disappear against the grey background and for the Red bar to look black as shown below:



The colours of the Red and Cyan bars and the grey background may be adjusted by selecting the ... buttons next to the corresponding colour.  This will display a colour picker windows as shown below:



The colour displayed on the device will be adjusted in real time as you change the colour selected on the Colour Picker.  When you are content that the optimum colour is selected, select OK.


Calibrate Duochrome Colours


The Thomson Near Chart includes a duochrome test for checking the status of a near refractive error.  It is important that the Red and Green used for  this test have approximately the same brightness to avoid a bias in the patient's response.


To check this, select the Calibrate Duochome Colours tab as shown below.



A duochrome test will be displayed on the device.  Check that the Red and the Green are approximately the same brightness.  If they are not, the brightness can be changed by selecting the ... buttons next to the corresponding colour.


Saving calibration settings


To save the calibration settings and return to the main program, select EXIT Calibration.


The calibration settings are stored on the Cloud Server.  This means that these settings will be used automatically if you select this device from another PC running the Thomson Near Chart.  This allows a device to be used in different rooms within a practice without having to recalibrate the device.