Eye tracking as a digital biomarker in neurodegenerative diseases

Oculomotor abnormalities are a common finding in neurodegenerative diseases due to degeneration of neural pathways and brain regions involved in controlling eye movements. Pathological changes to the dorsolateral prefrontal cortex, basal ganglia, superior colliculus and cerebellum produce subtle changes in eye-movement metrics that may not be detected by clinical examination. The present review addresses the potential use of eye-movement biomarkers in neurodegenerative conditions such as multiple sclerosis, Parkinson's disease, Alzheimer's disease and other dementias, and amyotrophic lateral sclerosis. Eye-movement metrics such as saccades, anti-saccades, fixation and smooth pursuit are prognostic of disease progression, can differentiate pathologic subtypes as an aid to diagnosis, and enable clinicians to evaluate early worsening of motor and cognitive function. The cost of medical technologies limits their optimal use and accessibility in clinical practice. The shortage of subspecialist neurologists further limits access to care. New eye-tracking technologies incorporated into widely-accessible digital devices such as smart phones and tablets now permit detailed assessments with minimal equipment requirements, providing an important non-invasive and potentially cost-effective method for patient evaluation in routine clinical practice and as an aid to treatment decision-making. Digital biomarkers can be readily employed by healthcare professionals such as family physicians, nurses and pharmacists to bridge the care gaps, potentially providing them with powerful tools that can be broadly adopted to improve the delivery of care to patients with neurodegenerative conditions.