Colours
Test Chart 2016 makes use of colours for a number of the tests. As the exact colour reproduction of monitors varies to some extent, the software allows the colours to be adjusted.
Colours can be changed by clicking on the corresponding Change... button. This will automatically display a sample chart on the main test chart screen and display the Colour picker dialogue box as shown below.
The colour is changed by varying the R,G and B settings using the sliders.
The Colours tab of the Program Options window includes the following panels
Test Chart 2016 allows the foreground and background colour of the LogMAR, Snellen and Single letter test charts to be changed. Five different colour combinations can be predefined and the user may then rotate around the five colour combinations by selecting the M icon on the toolbar or pressing M on the keyboard or remote.
See Coloured chart
The five colours may be defined by selecting the Colour no. (1-5) in the pull-down list and selecting the required colour for the Background colour and the Optotype colour using the colour picker controls. A simulation of the current colour combination is shown and a Name may be given to each colour combination. Select Save to save the new set of colour combinations.
Current line marker
The LogMAR, Snellen and Single letter test charts have a line in the centre of the screen to identify the current row. The colour of this line may be changed or the line hidden.
The duochrome test provides a useful method for fine-tuning a refraction. If a target appears to be darker on the green background the prescription is under-plused or over-minused and vice versa if the targets appear to be sharper on the red background.
For this test to work reliably, the brightness of the red and the green should be well-matched.
Test Chart 2016 includes a distance and a near duochrome test (using the tablet interface). The exact colour of the red and green can be adjusted using the Red and Green colour picker controls. The test generally works best with a pure red and pure green but some adjustment may be required to ensure that the red and green backgrounds are approximately the same brightness. If either colour is significantly brighter than the other it can bias the response.
This is best done subjectively by viewing the test from the patient's viewpoint and ensuring that adding a +0.25 and -0.25 lenses has the expected effect.
Fixation Disparity colours (Non Polarised)
The fixation disparity test included in Test Chart 2016 has been developed and carefully evaluated at City University.
The patient views the screen binocularly through the red and green filters. The entire field except for the two monocular markers, is seen binocularly. The patient is asked to look at the cross in the centre and report if the markers above and below the cross are in a straight line. If they are mis-aligned, appropriate prisms or lenses are used to align them in the normal manner.
For the test to work well, the red bar should not be visible against the grey background when viewed through the red filter and the "green" (actually turquoise works best) bar should not be visible against the grey background when viewed through the green filter. Conversely the red bar should look "black" when viewed through the green filter and the green bar should look black when viewed through the red filter.
Test Chart 2016 is pre-set with default colours but because of differences in the colour reproduction of different monitors, some adjustment may be required to get an optimum match.
The colour of the Red, Green and Back(ground) can be adjusted for the distance and near tests using the corresponding colour picker controls. A degree of trial and error is required to optimise the settings.
Maddox Rod Bar colour
To implement a Maddox Rod test on a computer screen it is necessary to use a bar instead of a spot in order to achieve adequate brightness. The colour of the bar can be changed using the Maddox rod colour picker. Best results are obtained if the bar is matched in colour to the Maddox rod – i.e. a red bar for a red Maddox rod. If the streak produced by the Maddox rod is not bright enough, a White bar should be selected.