MORPHOLOGICAL CHANGES OF THE RABBIT CORNEA IN THE LATE TERMS AFTER THE SIMULATION OF A MECHANICAL NON-PENETRATING CORNEA INJURY AND ITS CORRECTION USING DECELLULARIZED XENOSTROMA

Abstract

Abstract. The global incidence of vision loss is estimated at 36 million per year, and one of the fi ve leading causes is injury or disease aff ecting the cornea. In some cases, damage to the cornea requires surgical intervention using xenografts.This study aims to investigate the peculiarities of the morphological changes of the rabbit cornea in the dynamics of experimental mechanical non-penetrating corneal injury and its correction with decellularized xenocorneal stroma.Material and methods. Experiments were performed on Chinchilla rabbits in compliance with the rules of bioethics. The animals were divided into three groups: I – animals without simulated pathology, II – animals with simulated mechanical nonenetrating corneal trauma, III – animals with corneal trauma that underwent surgical correction using pig corneal stroma obtained by the decellularization method. Animals were removed from the experiment 14 and 28 days after the beginning of pathology simulation. Rabbits of the second and third groups were subjected to a concentric epithelial incision in the upper half of the cornea of both eyes under local anaesthesia, within which the anterior epithelium was removed together with the upper layer of the corneal stroma with a disposable ophthalmic scalpel. The rabbits of the third group underwent corneal injury correction by closing the defect with decellularized pig xenocorneal stroma. For histological examination, pieces of the cornea were processed according to generally accepted methods. Para ffi n sections of the cornea were stained with hematoxylin and eosin. The thickness of the anterior corneal epithelium in the central and peripheral areas of the injury, the stroma’s thickness, and the cornea’s general thickness were determined morphometrically. The normal distribution determined the reliability of the diff erence between the data according to the student’s t-test. Diff erences were considered signifi cant at p<0,05.Results. Morphometrically established, the dynamic increase in the thickness of the anterior epithelium in the marginal zones up to 103.49±5.17 μm on the 14th day of the experiment, which is 1.44 times greater (p˂0,001) compared to the norm, and the thickness of the cornea, with the maximum value in the same period, to 759.42±27.12 μm, which exceeded the intact indicator by 2.39 times (p˂0.001). On the 28th day of the experiment, under the conditions of simulation of mechanical injury at the microscopic level, the closure of the defect with an epithelium of average thickness 60.27±2.01 μm with an uneven relief of the basal surface and areas of detachment from the substantia propria was revealed. In the upper layers of the stroma, signs of maturation of young connective tissue with the presence of fi broblastic and leukocyte cells, capillaries and disordered orientation of collagen fi bers are microscopically revealed. Morphometrically, on the 28th day, the substantia propria thickness of the second group animals is signifi cantly (p˂0.001) bigger than the norm but 1.56 times less compared to the 14th day of the experiment. Microscopically and morphometrically, it was established that under the condition of using a decellularized pig cornea for the correction of mechanical corneal trauma, hyperplasia of the epithelium of the marginal areas was most pronounced on the 14th day 126.37±5.06 μm, which resulted in the closure of the defect with a well-structured epithelial regenerate 35.20±1.07 μm without areas of exfoliation. These morphometric parameters signifi cantly (p˂0.001) exceeded those of similar groups of animals in the cornea without correction. In the same term, the dominance of cells of the fi broblastic series and the absence of morphological manifestations of infl ammation were recorded in the granulation tissue. It was histologically investigated that using a decellularized pig cornea 28 days after correction ensures the restoration of the typical structure of the cornea with the approximation of morphometric indicators to the group of intact animals. In contrast to the second experimental group, where no correction was performed, the renewed anterior epithelium of the central corneal zone of the animals of the third group had a clear diff erentiation into layers, an even relief of the basal surface and a contoured Bowman’s membrane. Its thickness 54.19±2.09 μm was unreliably diff erent from the norm. During this period of the experiment, when correction was applied, mature connective tissue and single capillaries in a state of reduction were histologically detected in the stroma, while the phenomena of maturation of connective tissue components were often observed in the cornea of the animals of the second experimental group. Microscopically, in the substantia propria, bundles of collagen fi brils were oriented parallel, which is one of the factors that ensure the cornea’s transparency.Conclusions. Microscopically and morphometrically, it was established that the use of decellularized pig cornea for the correction of mechanical corneal trauma improves the dynamics of regeneration, accelerates the maturation of granulation tissue, the healing of the defect, contributes to the structuring and restoration of the corneal morphology as close to normal as possible.