Before the software is used for the first time, the screen size must be calibrated.


NOTE

If the PC is using a single screen, the test field will be automatically set to the full screen size.  For PCs with dual screens, the screen to be used for testing must be selected from the Options .... Settings ... Windows position window before performing the Screen Size Calibration.


To calibrate the screen size, select the Options tab at the top of the screen and select Calibrate size. This will display a screen similar to that show below.



Measure the width of the visible area of the screen in mm and enter the result in the corresponding box.  Then do the same for the screen height.  The concentric circles will be redrawn to show the angular subtense of the screen  The vertical and horizontal angle subtended by the screen is displayed in the blue box.


If the angle subtended by the screen is less than that required by the test protocol (30-2 requires +/- 33 degs, 24-2  requires +/- 26 degs and 10-2  requires +/- 12 degs), the fixation target will be moved throughout the test so that the more eccentric stimuli can be tested.


The angle subtended by the screen can be increased by decreasing the viewing distance.  However, a viewing distance of less than 25 degrees is not desirable.


If a larger screen is being used, the viewing distance should be extended until the required eccentricity is just accommodated on the screen.