PURPOSE. We examined inferior oblique muscles from subjects with over-elevation in adduction for characteristics that might shed light on the potential mechanisms for their abnormal eye position. METHODS. The inferior oblique muscles were obtained at the time of surgery in subjects diagnosed with either primary inferior oblique overaction or Apert syndrome. The muscles were frozen and processed for morphometric analysis of myofiber size, central nucleation, myosin heavy chain (MyHC) isoform expression, nerve density, and numbers of neuromuscular junctions per muscle section. RESULTS. The inferior oblique muscles from subjects with Apert Syndrome were smaller, and had a much more heterogeneous profile relative to myofiber cross-sectional area compared to controls. Increased central nucleation in the Apert syndrome muscles suggested on-going myofiber regeneration or reinnervation over time. Complex changes were seen in the MyHC isoform patterns that would predict slower and more sustained contractions than in the control muscles. Nerve fiber densities were significantly increased compared to controls for the muscles with primary inferior oblique overaction and Apert syndrome that had no prior surgery. The muscles from Apert syndrome subjects as well as those with primary inferior oblique overaction with no prior surgery had significantly elevated numbers of neuromuscular junctions relative to the whole muscle area. CONCLUSIONS. The muscles from both sets of subjects were significantly different from control muscles in a number of properties examined. These data support the view that despite similar manifestations of eye misalignment, the potential mechanism behind the strabismus in these subjects is significantly different.
Bibliographical noteFunding Information:
Supported by National Institutes of Health (NIH) RO1EY15313 and EY11375 from the National Eye Institute (LKM), Minnesota Medical Foundation, Minnesota Lions and Lionesses, and an unrestricted grant to the Department of Ophthalmology from Research to Prevent Blindness, Inc.
© 2020 Association for Research in Vision and Ophthalmology Inc.. All rights reserved.
- Apert syndrome
- Extraocular muscle
- Inferior oblique
- Inferior oblique overaction
- Neuromuscular junctions
PubMed: MeSH publication types
- Journal Article
- Research Support, N.I.H., Extramural
- Research Support, Non-U.S. Gov't