09-04-2020, 03:16 PM
While some additional adjustments may be needed for participants who wear glasses, glasses generally does not present a problem for tracking with EyeLink systems. The two main issues you might encounter are glare/reflections from the lenses and the system mistakenly tracking the glasses' frames.
Addressing Glare/Reflections
Issues with Glasses Frames
With some glasses, it's possible that the eye tracker may suddenly try to track part of the glasses frame. This typically occurs when there is a small reflection that gets mistaken for the Corneal Reflection.
Addressing Glare/Reflections
- For all systems: Ask the participant to slightly tilt their head to change the angle of their glasses and minimize reflections.
- For the Desktop mount with the SR Research Head Support: the chin pad can move forward and backward by loosening the Chin Pad Position Knob at the bottom of the chinrest. Loosen the knob and adjust the tilt of the participants head until the reflection is no longer blocking the view of the eye before tightening the knob back to lock it into position.
- For the Tower mount: You can also adjust the angle of the hot mirror to reduce glare by loosening the two knobs along the top edge of the mirror which will allow you to adjust the angle of the mirror.
- For the Desktop mount with the SR Research Head Support: the chin pad can move forward and backward by loosening the Chin Pad Position Knob at the bottom of the chinrest. Loosen the knob and adjust the tilt of the participants head until the reflection is no longer blocking the view of the eye before tightening the knob back to lock it into position.
- Clean the lenses. Dirt or debris on the lenses can interfere with the camera's ability to see the eye, so please make sure the lenses are as clean as possible.
- Remote Mode Considerations: Glasses are usually fine in this mode, but it may be harder to control head movements that introduce glare. Changing or monitoring the particpants posture may help enforce proper orientation of the head.
Issues with Glasses Frames
With some glasses, it's possible that the eye tracker may suddenly try to track part of the glasses frame. This typically occurs when there is a small reflection that gets mistaken for the Corneal Reflection.
- To stop the system from tracking the glasses' frames instead of the eye, use the "Search Limits" feature by going to Camera Setup screen and enabling "Search Limits." Once enabled center the limits over the eye by clicking on the eye in the Global camera image, and resize the Search Limits ellipse to exclude any problematic reflections from the frames by holding ALT and using the arrow keys on the Host PC to modify the dimensions of the ellipse.
- With the EyeLink II some glasses frames can occasionally block the corneal reflection illuminators. If there is trouble tracking in Pupil - CR mode with glasses, try switching to Pupil Only mode.