June 2022
Volume 63, Issue 7
Open Access
ARVO Annual Meeting Abstract  |   June 2022
Biomechanical Simulation of Compartmental Superior Oblique (SO) Palsy
Author Affiliations & Notes
  • Qi Wei
    Bioengineering, George Mason University, Fairfax, Virginia, United States
  • Joseph L Demer
    Ophthalmology, University of California Los Angeles, Los Angeles, California, United States
    Neurology, University of California Los Angeles, Los Angeles, California, United States
  • Footnotes
    Commercial Relationships   Qi Wei None; Joseph Demer None
  • Footnotes
    Support  NIH R01EY029715
Investigative Ophthalmology & Visual Science June 2022, Vol.63, 2775 – A0310. doi:
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      Qi Wei, Joseph L Demer; Biomechanical Simulation of Compartmental Superior Oblique (SO) Palsy. Invest. Ophthalmol. Vis. Sci. 2022;63(7):2775 – A0310.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

Purpose : Histology and quantitative analysis in the past decade revealed that compartmentalization is a general feature of extraocular muscles (EOMs). Such discovery motivates consideration of strabismus potentially associated with compartmental pathology. We developed a biomechanical model and simulated the strabismus caused by compartmental SO palsy.

Methods : A new model simulating actively controlled pulley mechanics of the horizontal EOMs was developed recently (Wei and Demer, IOVS, 62: 2606, 2021). The orbital (OL) and global (GL) layers of the horizontal rectus EOMs, as well as the pulley sleeves and their suspensions, were explicitly modeled as coupled via elastic strands. The model was elaborated by adding these pulley modeling primitives to the vertical EOMs to enable realistic pulley simulation in tertiary gazes. Two mechanically-independent neuromuscular SO compartments (Suh et al., IOVS, 57:13:5535-5540, 2016) were explicitly modeled. The medial SO compartment tendon inserts more anteriorly and medially than the lateral compartment, while the two compartments share the same path from origin to trochlea. Independent innervations of the two SO compartments were assumed to model compartmental SO palsy. The neural controller minimized simulated eye velocity error and total innervation level during and after saccades. We simulated 25 fixational eye positions formed by 15o horizontal and vertical increments around central gaze. The controller estimated innervations of 11 actuators comprising 2 layers of each rectus EOM, 2 SO compartments, and one inferior oblique unit. Compartmental SO palsy was simulated by zeroing innervation of one SO compartment.

Results : Predicted innervations for fixations (Fig. 1) and saccades were consistent with previous computational work as well as known functions of EOMs and their compartments. Simulation of lateral compartment SO palsy (Fig. 2) predicted greater hypertropia than medial compartment palsy in infraduction, and less excyclotorsion in infraducted adduction, demonstrating differential mechanical functions of the two SO compartments.

Conclusions : An improved biomechanical model implementing realistic actively controlled pulleys and SO compartments provides a computational tool to examine compartmental functions of the SO muscle. Modeling might assist diagnosis of compartmental palsy, and be used to quantitatively predict the effectiveness of selective strabismus surgeries.

This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.

 

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