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The Effect of Ambient Light Conditions on Quantitative Pupillometry

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A Letter to the Editor to this article was published on 14 January 2019

A Letter to the Editor to this article was published on 02 January 2019

Abstract

Background

Automated devices collecting quantitative measurements of pupil size and reactivity are increasingly used for critically ill patients with neurological disease. However, there are limited data on the effect of ambient light conditions on pupil metrics in these patients. To address this issue, we tested the range of pupil reactivity in healthy volunteers and critically ill patients in both bright and dark conditions.

Methods

We measured quantitative pupil size and reactivity in seven healthy volunteers and seven critically ill patients with the Neuroptics-200 pupillometer in both bright and dark ambient lighting conditions. Bright conditions were created by overhead LED lighting in a room with ample natural light. Dark conditions consisted of a windowless room with no overhead light source. The primary outcome was the Neurological Pupil Index (NPi), a composite metric ranging from 0 to 5 in which > 3 is considered normal. Secondary outcomes included resting and constricted pupil size, change in pupil size, constriction velocity, dilation velocity, and latency. Results were analyzed with multi-level linear regression to account for both inter- and intra-subject variability.

Results

Fourteen subjects underwent ten pupil readings each in bright and dark conditions, yielding 280 total measurements. In healthy subjects, median NPi in bright and dark conditions was 4.2 and 4.3, respectively. In critically ill subjects, median NPi was 2.85 and 3.3, respectively. Multi-level linear regression demonstrated significant differences in pupil size, pupil size change, constriction velocity, and dilation velocity in various light levels in healthy patients, but not NPi. In the critically ill, NPi and pupil size change were significantly affected.

Conclusion

Ambient light levels impact pupil parameters in both healthy and critically ill subjects. Changes in NPi under different light conditions are small and more consistent in healthy subjects, but significantly differ in the critically ill. Practitioners should standardize lighting conditions to maximize measurement reliability.

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Funding

American Brain Foundation Crowdsourcing Grant

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Authors and Affiliations

Authors

Contributions

CO, MD, MPHS were responsible for study design, analysis, interpretation of results, and the writing of the manuscript. MH, BS assisted in statistical analysis of results and entering demographic and clinical data for patients. SS, MD, PHD oversaw study design and provided expertise regarding analysis and interpretation of results.

Corresponding author

Correspondence to C. Ong.

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Conflict of interest

The authors declare that they have no conflict of interest.

Ethical Approval

The study has been approved by the institutional ethics committee. For this type of retrospective study, formal consent is not required.

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Ong, C., Hutch, M. & Smirnakis, S. The Effect of Ambient Light Conditions on Quantitative Pupillometry. Neurocrit Care 30, 316–321 (2019). https://doi.org/10.1007/s12028-018-0607-8

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