Brain and Eye as Potential Targets for Ionizing Radiation Impact. Part Iv – Fetal Radiation-Induced Binocular Vision Disorders: A Pilot Study. Immunohistochemical Changes of Non-Irradiated Eyeball Muscles Affected by Strabismus. Evidence of a Possible Mechanism of the Strabismus Development in Persons Exposed to Fetal Radiation

Abstract

Strabismus is a significant cause of a decrease in the functional capabilities of the organ of vision, additionally, it leads to the deteriorating quality of life. Orbital factors and nervous system changes may play an important role in strabismus pathogenesis. There are few reports on binocular vision disorders in radiation-exposed persons. Functions of the external eyeball muscles might be disturbed based on the changed coordination process of subcortical nerve structures and due to altered metabolism. A carefully conducted research is necessary to clarify the possible pathogenesis of binocular vision disorders in radiation-exposed persons. Objective: to assess the peculiarities of the development of strabismus and binocular vision disorders in people who were exposed to ionizing radiation in utero; to investigate the changes in distribution and appearance of myosin, dystrophin, and collagen IV between non-irradiated persons with normal binocular vision and patients with strabismus. Materials and methods. 583 persons, irradiated in utero because of the Chornobyl disaster were examined (at the time of examination average age was 11.3 ± 0.1 years). The control group – 808 people – Kyiv residents. Overall, 15 non-irradiated eyeball muscle samples were examined. 10 were from strabismus patients and 5 were controls. To evaluate morphological structure haematoxylin and eosin staining were used. For the detection of myosin, dystrophin, and collagen IV biotin-avidin (IMH) immunohistochemistry method was performed. Semi-quantitative grading method was used for the evaluation of immunoreactive structure appearance and local distribution. Results. An increased frequency of divergent strabismus (p = 0.04190) and heterophoria (p = 0.002603) was found in the group exposed to prenatal (fetal) radiation because of the Chornobyl disaster compared to the control group. The relative risk of heterophoria was 5.08 (1.42 – 18.13). A decrease in dystrophin, myosin, and collagen IV positive structures was observed in non-irradiated strabismus-affected eyeball muscles compared to the control group. Conclusions. Detected changes indicate an increased probability in the development of strabismus in persons who had been exposed to fetal radiation. Non-irradiated strabismus-affected eyeball muscles are characterized by diminished myosin, dystrophin, and collagen IV immunohistochemical structures. Additionally, determined qualitative morphological changes in skeletal striated muscle fibers lead to the changed structural organization, indicating possible muscular dystrophy. Thereby, the presence of dystrophic processes in the eyeball muscles may play a significant role in the morphopatogenesis of strabismus. Further morphological studies are necessary to clarify the development of binocular vision disorder and the methods of their correction. These studies would be especially important to populations that were exposed to radiation. Key words: irradiated in utero, ionizing radiation, strabismus, eyeball muscles, immunohistochemical studies, pathogenesis.