Eye tracking for diagnosis and monitoring

Even a mild case of traumatic brain injury (mTBI) can lead to long-term impairment, so accurate and timely detection is vital¹. Eye movements involve many brain areas, thus visual impairments are a common finding following TBI, including mTBI². 

A mild cause of traumatic brain injury (mTBI) is challenging to objectively diagnose and has no universally accepted diagnostic criteria. The development of easily quantifiable techniques using eye tracking as an objective diagnostic tool provides practitioners with an objective tool that is easier to assess than conventional tests. Thus, as this technology becomes increasingly integrated into clinical settings, the potential for it to identify deficits accurately and reliably in patients following mTBI, and to monitor both their recovery and the effectiveness of potential treatments will increase¹. 

Concussion and mTBI tests for diagnosis and initial assessment consist of symptom checklists, sideline tests such as the King-Devick test, balance tests, head impact telemetry system, eye movement tracking devices, cognitive tests, magnetic resonance imaging, computed tomography, diffusion tensor imaging, functional magnetic resonance imaging, magnetic resonance spectroscopy, positron emission tomography and electrophysiology^3,4. However, at present, there is no single test that alone can reliably diagnose concussion or determine when recovery has occurred³. In addition, objective measures for diagnosing mTBI are needed and eye-tracking is a potential useful diagnostic tool for identifying mTBI^1,3. 

Approximately 90% of individuals with mTBI examined in a clinic setting and having vision-related symptoms were diagnosed with one or more oculomotor dysfunctions following their acute care phase and natural recovery period^1,5. Saccades, the head impulse test and pursuits are specific (97.0%) and sensitive (84.9%) in distinguishing healthy controls from participants with mTBI¹. 

With concussions, the clinical neuro-ophthalmic exam is also important for detecting abnormalities in fusional vergence, saccades, smooth pursuit, and visual fixation⁴. Common neuro-ophthalmic findings in concussion include abnormalities in saccades/antisaccades, smooth pursuit, vergence, accommodation, the vestibular–ocular reflex and photosensitivity^3,4. 

In the first 10 days after mTBI, patients had impaired anti-saccades, prolonged saccadic latencies, higher directional errors, poorer spatial accuracy, and impaired memory guided saccades³. Saccadic dysfunction as assessed clinically may be present in approximately 30% of patients with mTBI^3,6. Abnormalities in pursuit eye movements were present in 60% of mTBI patients^7,8. Convergence abnormalities have been reported in 47%–64% of patients with concussion^3,6. 

mTBI can negatively affect the maximum diameter, amplitude and velocity of the constriction and dilation of the pupil, which are all difficult to assess without computerised pupillometry^9,1. mTBI patients have small increases in constriction latency in response to light and reduced average constriction velocity as found in a non-randomised controlled trial¹. While mTBI typically adversely affects many aspects of the dynamics of the pupillary light reflex (PLR), the effects seen to be in both pupils, i.e. mTBI per se typically does not cause asymmetric pupillary damage and related asymmetric responsivity⁹. 

Vergence system abnormalities are also common in mTBI¹⁰. In fact, vergence system abnormality seems to be the most common dysfunction in mTBI, with studies showing that 56.3% of these patients had one or more vergence-related abnormalities^5,10. 

1. Cade A, Turnbull PR. Clinical testing of mild traumatic brain injury using computerised eye-tracking tests. Clin Exp Optom. 2022;105(7):680-686. doi:10.1080/08164622.2021.2018915
   
   
2. Sussman ES, Ho AL, Pendharkar AV, Ghajar J. Clinical evaluation of concussion: the evolving role of oculomotor assessments. Neurosurg Focus. 2016;40(4):E7. doi:10.3171/2016.1.FOCUS15610
   
   
3. Ventura RE, Jancuska JM, Balcer LJ, Galetta SL. Diagnostic tests for concussion: is vision part of the puzzle? J Neuro-Ophthalmol Off J North Am Neuro-Ophthalmol Soc. 2015;35(1):73-81. doi:10.1097/WNO.0000000000000223
   
   
4. Ventura RE, Balcer LJ, Galetta SL, Rucker JC. Ocular motor assessment in concussion: Current status and future directions. J Neurol Sci. 2016;361:79-86. doi:10.1016/j.jns.2015.12.010
   
   
5. Ciuffreda KJ, Kapoor N, Rutner D, Suchoff IB, Han ME, Craig S. Occurrence of oculomotor dysfunctions in acquired brain injury: a retrospective analysis. Optom St Louis Mo. 2007;78(4):155-161. doi:10.1016/j.optm.2006.11.011
   
   
6. Capó-Aponte JE, Urosevich TG, Temme LA, Tarbett AK, Sanghera NK. Visual dysfunctions and symptoms during the subacute stage of blast-induced mild traumatic brain injury. Mil Med. 2012;177(7):804-813. doi:10.7205/milmed-d-12-00061
   
   
7. Nerrant E, Tilikete C. Ocular Motor Manifestations of Multiple Sclerosis. J Neuroophthalmol. 2017;37(3):332-340. doi:10.1097/WNO.0000000000000507
   
   
8. Wilne S, Collier J, Kennedy C, Koller K, Grundy R, Walker D. Presentation of childhood CNS tumours: a systematic review and meta-analysis. Lancet Oncol. 2007;8(8):685-695. doi:10.1016/S1470-2045(07)70207-3
   
   
9. Ciuffreda KJ, Joshi NR, Truong JQ. Understanding the effects of mild traumatic brain injury on the pupillary light reflex. Concussion Lond Engl. 2017;2(3):CNC36. doi:10.2217/cnc-2016-0029
10. Thiagarajan P, Ciuffreda KJ, Ludlam DP. Vergence dysfunction in mild traumatic brain injury (mTBI): a review. Ophthalmic Physiol Opt J Br Coll Ophthalmic Opt Optom. 2011;31(5):456-468. doi:10.1111/j.1475-1313.2011.00831.x