Peculiarities of morphogenesis of orbit and organ of vision structures in human fetuses

Abstract

The aim of this work is to elucidate the features of morphogenesis, syntopic and morphometric changes in the structures of the orbit, neurovascular and muscular structures of the organ of vision in the fetal period of human ontogenesis.Material and methods. By means of complex of methods of morphological research (anthropometry, morphometry, microscopy, preparation, three-dimensional computer reconstruction and statistical analysis), 30 specimens of human fetuses of both sexes aged from 4 to 10 months of intrauterine development (IUD) (160.0-460.0 mm parietal-coccygeal length (PCL)) were studied. Computer tomography was used to study 17 human fetuses aged from 4 to 9 months of IUD (180.0-440.0 mm PCL).Results. At the end of the 5th month of IUD, an orbital index is 75%, which is noted in the transformation of the shape of orbit from flattened to rounded due to an increase in its vertical size relative to the horizontal one. We associate this transformation of the orbit with syntopic influence of adjacent regions: the growth of the lateral wall of the nasal cavity, development of the paranasal sinuses, and facial skeleton. At the end of the 5th week of intrauterine development, external eyeball muscles are finally differentiated from the common muscle rudiment. The analysis of changes in morphometric parameters of muscles of the eyeball made it possible to derive mathematical functions, that describe normal dynamics of growth of their length, as well as to reveal critical periods of their development in terms of the rate of changes in their thickness and width.Conclusions1. The development of the organ of vision in the fetal period of human ontogenesis is a complex process due to the coordinated interaction between morphological and morphometric changes in the orbit, eyeball and its muscles, nerves and vessels.2. Critical periods of development of the orbit and its structures is the 6th month of intrauterine development, during which there is an uneven growth rate of the size of the muscles of the eyeball, as well as the size of the orbit.3. At the 6th month of intrauterine development, uneven growth rates of the horizontal size of the orbit relative to the vertical one are observed, as a result of which its shape begins to return to the mesoconchal type characteristic of such prefetuses. Such age-related transformations of shape and size of the orbit are due to the growth of the eyeball, skull and face, which generally determines the shape of the orbit.4. Starting from the 8th month of fetal period of development, structure and topography of the structures of the orbit acquire signs of a definitive condition, the shape of the orbit is finally established, and uniform growth rates of all structures of the organ of vision are observed, except for the growth of the circumference of the orbit at the end of prenatal period of human ontogenesis.