Increased myofiber size and reduced satellite cell numbers in medial rectus muscle of patients with intermittent exotropia

Abstract

ABSTRACT Purpose To elucidate the differences in muscle bundle and satellite cells in medial rectus muscle through histological and Immunofluorescence studies of intermittent exotropia patients and normal controls. Materials and Methods: From January 2015 to December 2017, 15 patients who underwent medial rectus resection surgery at Kosin University Gospel Hospital were enrolled. Four medial recti muscles collected from two brain-dead men without strabismus were used as controls and compared with the intermittent exotropia group. Hematoxylin and eosin (HE) staining were performed, and all muscle bundle diameters were measured with the Image J program and compared to the mean value. Immunological staining for MyoHC (Myosin Heavy Chain), PAX7 (Transcription Factor), and PCNA (Proliferating Cell Nuclear Antigen) were performed to analyze the distribution of myocytes and PAX7-positive and PCNA-positive cells. Results: The mean ages of the strabismus and control groups were 17.33 ± 13.05 and 22.0 ± 5.85 years, respectively, and the male to female ratio was 7:2 and 2:0. The average angle of deviation in the exotropia patients was 36.0 ± 16.83 prism diopters. The mean muscle bundle diameter under light microscopy was 60.21 ± 1.48 in the exotropia group and 52.27 ± 0.74 in the control group. The exotropia group showed significantly greater mean muscle bundle diameter (p < .001) and diameter regularity than the control group. The PAX7(+)/muscle bundle number ratio was 0.016 ± 0.014 and 0.056 ± 0.015 in the exotropia group and control group, respectively (p < .001), and the PCNA(+)/muscular bundle number ratio was 0.015 ± 0.017 and 0.182 ± 0.102 (p < .001). Both were significantly higher in the control group compared to that in the exotropia patients. Conclusion: In the exotropia group, mean diameter of medial rectus muscle bundle was significantly larger than that of control group. The ratios of PAX7 and PCNA to muscle bundle number were significantly higher in the control group than intermittent extropia group. We found the negative relationship between activation of satellite cells and muscle bundle diameter, and it might take one step forward to elucidate the pathogenesis of intermittent extropia.