Bifocals and trifocals are glasses with two or three levels of magnification respectively. The upper pane(s) are to correct nearsightedness while the lower pane is to correct farsightedness (i.e., the ability to see things up close).
The Eye Tracker can potentially misread pupil size changes due to the magnification changes that occur with bifocals or trifocals when the examinee tilts their head.
If an examinee uses bifocals or trifocals, the service provider should:
1) In the Test Create dialog box, set the font to the largest size, which is 20 points. Then determine if the examinee can read the text on screen without the use of glasses.
2) If the previous option does not resolve the issue, please provide the examinee with a set of non-glare reading glasses. Reading glasses are relatively inexpensive and can be purchased in magnifications ranging from 1.0x to 4.0x. Converus suggests having one pair of glasses of each magnification on hand.