Fixational eye movements: Implications for applied and clinical assessments

Clinicians can use fixational eye movements to gain more information about the state of their patients: these measures have great potential as biomarkers of health conditions and might facilitate the early and differential diagnosis of disease. Objective measurements of fixational eye movements are also increasingly used to quantify fatigue and other traits or symptoms. However, the validity of such assessments depends on our ability to identify and control for factors that potentially alter fixational eye movements and that thereby may confound the results. Because eye movements can drive neural activity, cognition, and perception, these potentially confounding factors should be addressed, even in tasks and conditions where eye movements are not the focus of the assessment. In this chapter, we review altered or abnormal microsaccade dynamics in neurologic and ophthalmic conditions. We also review various factors that are known to alter fixational eye movement measurements, including arousal, fatigue, substance use, and various other states that are common among patient and control populations. Taking these different factors into consideration may help clarify existing findings, help refine assessment and diagnostic tools, and help us to better understand human neurology.