What does a "fixation error" indicate during the FDT test?

A "fixation error" during the Frequency Doubling Technology (FDT) test indicates that the patient looked away from the central black dot during the test. This is significant because maintaining focus on the black dot is essential for accurately assessing the visual field. If the patient fails to keep their gaze fixed, it can lead to unreliable results, as the patient's awareness of stimuli may be compromised.

The test is designed to measure contrast sensitivity and field defects, and any movement or distraction can interfere with the interpretation of the visual field data. Thus, a fixation error serves as a critical indicator that might suggest a need to modify the testing conditions or provide further instruction to the patient. This will ensure that the results reflect the patient's true visual capabilities rather than any distractions or miscommunication during the test process.