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Linda K. McLoon, Justin Kohl, David Stager, Jr.; Innervational Changes in Inferior Oblique Muscles from Patients with Over-Elevation in Adduction. Invest. Ophthalmol. Vis. Sci. 2011;52(14):2078.
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Over-elevation in adduction is seen in patients with a variety of diagnoses, including primary inferior oblique overaction (IOOA), craniofacial dysostosis (CFD), and superior oblique palsy. The extraocular muscles open a window to look at brain control of eye position. However, little is known about potential adaptations in the inferior oblique muscle (IO) that might play a role in the final abnormal eye position.
IO muscles were obtained from 5 groups of subjects: patients with IOOA and no prior surgery, IOOA with prior surgery, CFD and no prior surgery, CFD with prior surgery, and controls. All muscles were frozen, immunostained for Schwann cell myelin, and analyzed morphometrically to determine myelinated nerve density in square microns.
The myelinated nerve density of normal human IO was 3.4+0.5. In patients with either CFD or IOOA who had prior surgery, myelinated nerve density was significantly decreased compared to normal. Mean myelinated nerve density in IOOA patient muscles was 1.66+0.27, a 2-fold decrease from control. Myelinated nerve density the CFD patient muscles was 4- or 2-fold less than control, 0.66+0.16 with prior surgery and 1.8+0.2 with no prior surgery. In the patients with IOOA and no prior surgery, there was no significant difference compared to control IO. The decreased myelinated nerve density in the CFD patient muscles correlates with significantly decreased myofiber size in their IO.
It is counterintuitive that the IO from patients with CFD or IOOA and prior surgery had significantly reduced myelinated nerve density compared to normal IO and when compared to the IO from patients with IOOA but no prior surgery. These results suggest several testable hypotheses. 1. There may be a specific loss of myelination in innervating nerves. 2. Surgery may result in decreased nerve density due to injury or adaptation. 3. Patients for whom primary surgery fails may be more likely to have abnormal levels of innervation. 4. Despite eye position, the primary problem may be in the antagonist muscles of the same eye. Future studies will attempt to answer these questions.
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