The fixation disparity test included in the Thomson Test Chart has been developed and carefully evaluated at City University. The new design has a number of advantages over the test included in earlier versions of Test Chart 2000 and is designed to work with red / green glasses rather than red/blue. This reduces the tendency for patients to suppress the left eye (which was a problem with earlier versions). The new test also provides a better stimulus for accommodation and improved binocular lock.


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 misaligned, appropriate prisms or lenses are used to align them in the normal manner.



Horizontal fixation disparity



 Vertical fixation disparity


NOTE: Research has shown that results obtained using this test correlate very well with conventional tests of fixation disparity. However, the Thomson Test Chart includes an option for using a polarised mask or a polarised screen for those who feel uncomfortable with using red/green dissociation.