Study in Patients With Unilateral Horner Syndrome Supports the Role of Müller's Muscle in the Eyelid-Dark Reflex.

Invest Ophthalmol Vis Sci

The Goldschleger Eye Institute, Sheba Medical Center and the Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel.

Published: November 2023

AI Article Synopsis

  • A study was conducted to investigate how Müller's muscle affects eyelid movement when lighting conditions change from bright (photopic) to dark (scotopic).
  • The research involved patients with unilateral Horner syndrome, comparing their affected eyes (with sympathetic nerve damage) to the unaffected eyes using advanced imaging techniques.
  • Results showed that eyelid retraction in response to dim light was significantly less in the affected eyes, suggesting that Müller's muscle plays a crucial role in this reflex.

Article Abstract

Purpose: A previous study demonstrated upper eyelid retraction synchronized with pupil dilation following a transition from photopic to scotopic conditions. The current study aimed to evaluate the role of Müller's muscle as the efferent arm of this suggested reflex arc.

Methods: A video scan of both eyes of patients with unilateral Horner syndrome was performed using optical coherence tomography infra-red mode to document the transition between photopic and scotopic conditions. The affected side with sympathetic denervation was the study group, whereas the contralateral unaffected side of the same patients served as the control group. The pupil diameter, upper eyelid margin-to-reflex distance 1, lower eyelid margin-to-reflex distance 2, and vertical palpebral fissure height were measured. The control group was compared to the healthy subjects of a previous study to verify any compensatory changes to the side contralateral to denervation.

Results: Ten patients with unilateral Horner Syndrome were included in the study. Transitioning from photopic to scotopic conditions, the mean change in margin-to-reflex distance 1 in the study and control groups was 315 ± 276 µm (P < 0.05) and 723 ± 432 µm (P = 0.005), respectively. Margin-to-reflex distance 1 and palpebral fissure height were significantly higher in the control group both in photopic (P = 0.005 and P = 0.017, respectively) and scotopic conditions (P = 0.005 and P = 0.007, respectively). The change in margin-to-reflex distance 1 and palpebral fissure height following the transition from light to dark was significantly greater in the control group (P = 0.022).

Conclusions: Reflexive eyelid retraction following a transition from photopic to scotopic conditions was significantly diminished in eyelids with sympathetic denervation compared with the unaffected contralateral side of the same patients. This study provides further evidence that the sympathetically innervated Müller's muscle serves as the efferent arm of this reflex.

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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC10683770PMC
http://dx.doi.org/10.1167/iovs.64.14.35DOI Listing

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