FAQ: Can the EyeLink systems be used with someone with astigmatism?

[Sam]

You can typically track participants with astigmatism. However, due to the shape of the eye in astigmatism, the corneal reflection can become distorted or lost when the participant looks toward the edges of the screen, especially the top corners.

If you encounter this issue, follow these troubleshooting steps in order.

1. Adjust the Camera Position
   If tracking is lost primarily at one of the top corners, try moving the Desktop camera mount toward that side of the monitor. Make small adjustments (1-2 cm at a time) and then recalibrate. Repeat this until the eye can be tracked reliably across all four corners.
   
2. Check the Physical Setup
   If adjusting the camera mount doesn't solve the problem, or if tracking is poor at both top corners, the issue is likely with the overall physical setup.
   • Adjust Viewing Distance: Move the display monitor further away from the participant to ensure it's within the system's optimal trackable range. Our online Calibration Coordinate Checker is a great tool for verifying the correct distance.
     
   • Adjust Vertical Position: Lower the display monitor or raise the participant's chair. The participant's eyes should be level with the top 25% of the screen.
     
   For more detailed guidance, please review the video tutorials for your specific system:
   • EyeLink 1000 Plus Setup and Usage Training Videos
     
   • EyeLink Portable Duo Setup and Usage Video Tutorials
     
3. Use a 5-Point Calibration
   If the steps above do not resolve the issue, and it is not critical for your experiment to have precise data from the corners, you can switch to a 5-point (HV5) calibration. This avoids the problematic corner targets entirely.