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Functional morphometry of horizontal rectus extraocular muscles during horizontal ocular duction
Robert A Clark1, Joseph L Demer
1Departments of Ophthalmology, David Geffen Medical School, University of California, Los Angeles, California 90095-7002, USA.
Investigative Ophthalmology & Visual Science
|September 22, 2012
Summary
Magnetic resonance imaging (MRI) measures of extraocular muscle (EOM) morphology accurately quantify contractility. Changes in cross-sectional area and posterior partial volumes correlate strongly with eye movement (duction).
Area of Science:
- Ophthalmology
- Medical Imaging
- Biomechanics
Background:
- Extraocular muscle (EOM) morphology is crucial for understanding eye movement.
- Quantitative magnetic resonance imaging (MRI) measures can assess EOM contractility.
- Previous methods lacked precise correlation with functional EOM changes.
Purpose of the Study:
- To identify the optimal MRI-derived quantitative measure of horizontal rectus EOM morphology that best correlates with eye movement (duction).
- To establish a reliable imaging biomarker for EOM contractility.
Main Methods:
- Coronal MRI scans were acquired in normal volunteers at various gaze positions (adduction, abduction).
- Duction angles were determined by globe-optic nerve junction displacement.
- Cross-sectional areas and partial volumes of horizontal rectus EOMs were calculated.
Main Results:
- All measured EOM morphologic parameters significantly correlated with duction angle (P < 0.0001).
- Maximum change in cross-sectional area in single image planes showed high correlation (R² = 0.91-0.92).
- Changes in posterior partial volumes, especially when combined with antagonist muscles, provided excellent contractility measures (R² = 0.86-0.95).
Conclusions:
- EOM morphologic changes measured by MRI are highly correlated with duction and contractility.
- Both single-plane maximum cross-sectional area changes and posterior partial volume changes offer accurate, quantitative assessments of EOM contractility.
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