Early recognition and treatment of major depressive disorder (MDD) is recognized as an important opportunity to improve patient outcomes.1 A reliable biomarker for early MDD has yet to be identified but this is currently an area of active research interest. During a poster presentation at the annual Canadian Psychiatric Association (CPA) conference in Vancouver in October, 2023, researchers from the Centre for Neuroscience Studies at Queen’s University in Kingston, Ontario, showcased the potential for eye tracking to probe for depression pathology in adolescents.
Eye movements as a biomarker for MDD
It has long been recognized that eye reactions and movements can provide insights into cognitive functioning and emotional processing.2 Recent advances in technology have led to the development of sophisticated tools that can accurately measure saccades, which are rapid eye movements that shift the centre of gaze from one location in the visual field to another, and how these can be altered by mood disorders.2 This makes them potential novel biomarkers for the early recognition of MDD.
Rapid eye movements provide insights on neural functions that can be impacted by MDD
Studies utilizing specialized eye tracking software in adults support the validity of changes in eye movements as a biomarker for early identification of MDD.3 Indeed, individuals with MDD have shorter fixation duration (i.e., amount of time the eyes rest on a stimulus) than healthy controls, and this can be remediated by cognitive behavioural therapy (CBT).3 Importantly, changes in fixation and saccade amplitude correlate with reductions in PHQ-9 depression scores, suggesting that eye tracking could be an objective method for diagnosing and monitoring response to depression treatment.3
Studying eye movements in adolescent MDD
Noninvasive biomarkers for early depression could be particularly useful in adolescent MDD, yet this is a relatively less studied population compared to adults. A group of neuroscience researchers from Queen’s University posited that known impairments in the frontal cortex, basal ganglia and limbic cortex of depressed adolescents might translate into altered saccade, pupil, and blink behaviour during a standardized eye tracking test. To test their hypothesis, they compared 79 healthy adolescents and 26 adolescents (mean age 16 years) with MDD using the Eye-Link 1000 Plus eye tracking system, which measures eye movements in response to pro- and anti-saccade video tasks. Saccades are rapid, ballistic eye movements that abruptly change the point of fixation. A pro-saccade task involves fixing the gaze on a central dot, then moving the gaze toward a target dot in the peripheral visual field as quickly as possible.3 An anti-saccade task is a measure of inhibitory control since it involves the voluntary suppression of the reflexive impulse to gaze toward a peripheral visual stimulus. Preliminary results from the Queen’s study showed several significant differences between depressed and healthy adolescents with respect to eye movement behaviour including increased express (rapid) and increased error rate in pro- and anti-saccade trials, and changes in pupil constriction and dilation intervals and blink rate during fixation tasks.
Eye movements were significantly altered in depressed vs healthy adolescents
Novel noninvasive biomarkers for depression
These observations suggest that non-invasive eye movement tests can potentially differentiate adolescents with depressive disorders from healthy adolescents. Studies in adults have shown that eye tracking can also distinguish between specific types of depression (e.g., unipolar vs bipolar).2 Other advances in eye tracking technology are being actively researched for their potential to identify and monitor individuals with depression. For example, smartphone sensors and apps can detect behavioural markers of depression and passive mobile phone data can be used to continuously screen for and monitor changes in depressive symptom severity.4
Smartphone apps are being investigated as a tool to identify and monitor depressive symptomatology
The Queen’s research group concluded that eye-tracking tools could be a valuable instrument to non-invasively probe depression in adolescents and to identify novel biomarkers for earlier identification of adolescent mental health disorders. Further studies in larger samples are warranted to validate these early but exciting findings.
Our correspondent’s highlights from the symposium are meant as a fair representation of the scientific content presented. The views and opinions expressed on this page do not necessarily reflect those of Lundbeck.
