Polarised Fixation Disparity tests

The fixation disparity test provides a rapid way of detecting the presence of a vertical or horizontal fixation disparity and determining the appropriate prismatic or refractive correction.

There  are three fixation disparity options available with the Polarised Mask.  These are selected by selecting the corresponding icon in the Secondary Toolbar or by pressing 1, 2 or 3 on the keyboard or the remote.

The first test option displays the vertical and horizontal markers allowing the presence of horizontal or vertical fixation disparity to be detected simultaneously.

With the polarised visor placed in front of the patient's eyes, one vertical and one horizontal bar is seen by right eye and the others by the left eye while the rest of the screen and the surround is seen binocularly.

The recommended routine is as follows:

1. Without the polarised visor, ask the patient to look at the red cross and confirm that the bars above and below and to the left and right are both in a straight line.
2. Put the polarised visor in place and ask the patient if the bars still appear to be in a straight line.
3. If the patient reports that the bars are misaligned, use appropriate prism to re-align them. The minimum prism required to re-align the markers is recorded.




While the first option provides a quick method for detecting the presence of fixation disparity, some patients may find it difficult to make simultaneous judgements about the alignment of the vertical and horizontal bars.  If this is the case, horizontal and vertical fixation disparity can be tested separately by selecting options 2 or 3 (see below).