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The Silent Symphony of Pupil: Decoding Constriction and Dilation Velocities in Neurological Health

by | Sep 1, 2025 | Manuscripts | 0 comments

Pritam Dutta, M. Optom.

Assistant Professor, Ridley College of Optometry, Jorhat, India

 
Pupillary assessment is a fundamental aspect of neurological examinations, offering insights into the autonomic nervous system and overall brain function. While traditional evaluations focus on pupil size and reactivity, analysing the velocities of pupillary constriction and dilation provides a deeper understanding of neural pathways and potential neurological impairments. (1) The Pupillary Light Reflex (PLR) involves the constriction and subsequent dilation of the pupil in response to light stimuli. (2)

Constriction velocity refers to the speed at which the pupil narrows when exposed to light, while dilation velocity denotes the speed at which the pupil returns to its baseline size after the light is removed. These dynamic responses are regulated by the parasympathetic and sympathetic branches of the autonomic nervous system, respectively. (2)

Clinical Significance of Constriction and Dilation Velocities

  • Neurological Assessment: Quantitative measurements of constriction and dilation velocities can aid in detecting neurological dysfunctions. For instance, a study highlighted that higher Glasgow Coma Scale (GCS) scores are associated with faster dilation velocities, suggesting that reduced dilation speed may indicate more severe brain injury. (1)
  • Autonomic Function Evaluation: Dynamic pupillometry serves as a tool to assess autonomic nervous system function. Research has shown that indices such as Maximum Constriction Velocity (MCV) and Absolute Constriction Amplitude (ACA) are lower in patients with significant autonomic failure compared to healthy controls, indicating impaired parasympathetic activity.(2)
  • Detection of Intracranial Pressure Changes: In patients with acute head injuries, monitoring constriction velocity can provide early indications of elevated Intracranial Pressure (ICP). A study found that reductions in constriction velocity were associated with increased ICP, under-scoring the importance of pupillary dynamics in critical care settings. (3)
  • Assessment of Neurological Pupil Index: The Neurological Pupil Index (NPi) is an algorithm that quantifies pupillary light reflex parameters, including constriction velocity. Research indicates that while there is a relationship between NPi and constriction velocity, discrepancies can occur. For example, brisk constriction velocity does not always correlate with a normal NPi, suggesting that comprehensive pupillary assessment should consider multiple parameters. (4)

    • Pupillary constriction and dilation velocities have been widely studied as potential biomarkers for autonomic and neurological functions. Recent research has explored their significance in various clinical conditions, including sepsis, anaesthesia-induced hypotension, sleep disorders, and neuro-developmental changes. (1-4) Table 1 provides a comprehensive summary of seven recent studies that investigated pupillary velocity dynamics, highlighting their objectives, key findings, and clinical implications. These studies emphasise the role of pupillometry in assessing autonomic dysfunction, predicting neurological outcomes, and understanding cortical modulation of pupillary responses.

Study Objective Key Findings
Uhrenholt et al. (2024)6 To observe the dilation velocity of the pupillary light reflex in Intensive Care Unit (ICU) patients with and without septic shock. Septic shock was associated with a slowed dilation velocity of 0.3 mm/s, suggesting changes in sympathetic autonomic tone.
Shao et al. (2022)4 To assess if pupil maximum constriction velocity predicts post-induction hypotension in patients with lower American Society of Anesthesiologists (ASA) status. Lower maximum constriction velocity was associated with a higher risk of post-induction hypotension, indicating its potential as a predictive tool.
Peinkhofer et al. (2019)7 To systematically review cortical modulation of pupillary function. Highlighted the role of cortical areas in modulating pupillary responses, suggesting that pupillary dynamics can reflect cortical activity.
DiNuzzo et al. (2019)8 To investigate brain networks underlying the pupil dynamics of the eyes. Identified specific brain networks involved in controlling pupil dynamics, emphasising the complexity of neural control over pupillary responses.
Vyas et al. (2015)9 To evaluate pupillary constriction velocity and latency as predictors of excessive daytime sleepiness. Found that both constriction velocity and latency correlated with subjective sleepiness measures, suggesting their utility in assessing daytime sleepiness.
Winston et al. (2019)10 To determine if variables of the pupillary light response mature with age and sex in a healthy paediatric cohort. Results revealed maturation of the pupillary light response by age and sex, providing normative benchmarks for comparison in health and disease.
Bremner (2012)11 To evaluate the dynamics of the pupillary response to a brief light stimulus. Demonstrated a strong linear correlation between amplitude and peak velocity of constriction in normal subjects, providing insights into the mechanical properties of the pupil response.

Table 1: Table of Recent Studies Focusing on Pupillary Constriction and Dilation Velocities

Incorporating the analysis of constriction and dilation velocities into pupillary assessments enriches the understanding of the neurological autonomic status of the patient. These measurements offer objective data that can inform diagnosis, monitor disease progression, and guide therapeutic interventions. As technology advances, the role of quantitative pupillometry in clinical practice is poised to expand, providing deeper insights into the complex interplay between the nervous system and pupillary dynamics.

References

  1. Thakur B, Nadim H, Atem F, Stutzman SE, Olson DM. Dilation velocity is associated with Glasgow Coma Scale scores in patients with brain injury. Brain Inj. 2021;35(1):114-8. doi: 10.1080/02699052.2020.1861481. PMID: 33347373.
  2. Muppidi S, Adams-Huet B, Tajzoy E, Scribner M, Blazek P, Spaeth EB, et al. Dynamic pupillometry as an autonomic testing tool. Clin Auton Res. 2013;23(6):297-303. doi: 10.1007/s10286-013-0209-7. PMID: 23880969.
  3. Shinder R, Szirth BC, He W, Frohman LP, Turbin RE. Amplitude, latency and constriction/dilation velocity of an afferent pupillary defect as measured with a pupillometer. Invest Ophthalmol Vis Sci. 2007;48(13):5538.
  4. Shao L, Zhou Y, Yue Z, et al. Pupil maximum constriction velocity predicts post-induction hypotension in patients with lower ASA status: a prospective observational study. BMC Anesthesiol. 2022;22:274. doi: 10.1186/s12871-022-01808-0.
  5. Bremner FD. Pupillometric evaluation of the dynamics of the pupillary response to a brief light stimulus in healthy subjects. Invest Ophthalmol Vis Sci. 2012;53(11):7343-7.
  6. Uhrenholt S, Linér SM, Stokholm J, Christensen T, Bestle MH. Pupillary dilation velocity is reduced in intensive care unit patients with septic shock. Acta Anaesthesiol Scand. 2024;68(1):56-62. doi: 10.1111/aas.14327. PMID: 37722925.
  7. Peinkhofer C, Knudsen GM, Moretti R, Kondziella D. Cortical modulation of pupillary function: systematic review. PeerJ. 2019;7:e6882. doi: 10.7717/peerj.6882. PMID: 31119083; PMCID: PMC6510220.
  8. DiNuzzo M, Mascali D, Moraschi M, Bussu G, Maugeri L, Mangini F, et al. Brain networks underlying eye’s pupil dynamics. Front Neurosci. 2019;13:965. doi: 10.3389/fnins.2019.00965. PMID: 31619948; PMCID: PMC6759985.
  9. Umesh V, Tucker WB. Pupillary constriction velocity and latency to predict excessive daytime sleepiness. Int J Clin Med. 2015;6:805-12.
  10. Winston M, Zhou A, Rand CM, Dunne EC, Warner JJ, Volpe LJ, et al. Pupillometry measures of autonomic nervous system regulation with advancing age in a healthy pediatric cohort. Clin Auton Res. 2020;30(1):43-51. doi: 10.1007/s10286-019-00639-3. PMID: 31555934.
  11. Bremner FD. Pupillometric evaluation of the dynamics of the pupillary response to a brief light stimulus in healthy subjects. Invest Ophthalmol Vis Sci. 2012;53(11):7343-7. doi: 10.1167/iovs.12-10881. PMID: 23036998.

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