THE LIGHT MICROSCOPIC VISUALIZATION OF THE OF THE SUS SCROFA DOMESTICUS ANTERIOR CORNEAL EPITHELIUM SUPRA-EPITHELIAL LAYER

According to the data of electron microscopy of chemically fixed material preparations, the surface of the anterior corneal epithelium is formed by myriads of microvilli. Smoothing of the surface of the anterior epithelium is attributed to the function of the tear film. As evidence confirming the existence of the tear film, interference patterns observed under certain conditions on the surface of the cornea are cited, which explain this optical phenomenon by the reflection of light from the anterior and posterior surfaces of the lipid layer of the tear film. In histological preparations of material cryofixed in vivo, the tear film is identified with the homogeneous material above the microvilli of the flat cells of the third layer of the anterior epithelium. It is assumed that the membrane-like structure on the surface of this homogeneous material may correspond to the lipid layer of the tear film. At the same time, the results of microscopy of cryostat section preparations prove that the anterior corneal epithelium consists of five cell layers. The fifth homogeneous layer consists of compacted rows of without nuclear cells. A thin membrane-like component is also present on its surface. There are no data on this membrane-like component of the anterior epithelium in the scientific literature. This means that a detailed description of the structure of the anterior corneal epithelium remains incomplete. The aim of the study was to obtain data on the membrane-like component of the anterior corneal epithelium. The material for the study was the eyes of a domestic pig (Sus scrofa domesticus). The method of the study was light microscopy. As a result of studying the sagittal cryostat sections of the cornea and imprint preparations from the surface of the cornea, the supra-epithelial layer of the anterior epithelium was visualized as a non-cellular component in the form of a film. The main elements of the film are microbubbles that outwardly resemble cell fragments and apoptotic bodies. We designated the non-cellular component as «supraepithelial film» layer. There is reason to believe that it is formed as a result of apoptosis of the surface cells of the anterior corneal epithelium in the liquid environment of the lacrimal fluid. To our knowledge, the published data are the first report of the presence of a non-cellular component in the form of a film on the surface of the anterior corneal epithelium. The structure and properties of the supraepithelial film are subject to comprehensive study to determine its role and significance in the physiology of the anterior epithelium. When discussing the nature of interference patterns on the corneal surface, the supraepithelial film present at the interface of two media (solid - anterior epithelium and liquid - lacrimal fluid), in our opinion, can be considered as the material basis of thin-film interference.

1. Bron A, Tripathi R, Tripathi B. Wolff's Anatomy of the Eye and Orbit. 8th edition. Taylor & Francis. 1998.- Р.752

2. McTigue JW. The human cornea: a light and electron microscopic study of the normal cornea and its alterations in various dystrophies. Trans Am Ophthalmol Soc. 1967;65:591-660

3. Pfister RR. The normal surface of corneal epithelium: a scanning electron microscopic study. Invest Ophthalmol. 1973;12:654-668

4. Nichols B, Dawson CR, Togni B. Surface features of the conjunctiva and cornea. Invest Ophthalmol Vis Sci. 1983;24:570-576

5. Collin SP, Collin HB. A comparative SEM study of the vertebrate corneal epithelium. Cornea. 2000;19:218-30. https://doi.org/10.1097/00003226-200003000-00017

6. Fuks E. Uchebnik glaznykh bolezney. M., Gos. Med. Izd., 1933.- In Russian

7. Arkhangel'skiy VN. Mnogotomnoe rukovodstvo po glaznym boleznyam: V 2-kh kn. 1962.-S.346. In Russian

8. Mishima S. Some physiological aspects of the precorneal tear film. Arch Ophthalmol. 1965;73:233-241. https://doi.org/10.1001/archopht.1965.00970030235017

9. Wysenbeek YS, Loya N, Ben Siro I et al. The Effect of Sodium Hyoluronote on the Corneol Epithelium. Investigative Ophthalmology and Visual Science. 1998;29(2):194-199

10. Chen HB, Yamabayashi S, Ou B et al. Structure and composition of rat precorneal tear film. A study by an in vivo cryofixation. Invest Ophthalmol Vis Sci. 1997;38:381-387

11. Ohashi Y, Dogru M, Tsubota K. Laboratory findings in tear fluid analysis. Clin Chim Acta. 2006;369(1):17-28. https://doi.org/10.1016/j.cca.2005.12.035

12. Masoudi S. Biochemistry of human tear film: A review. Exp Eye Res. 2022;220:109101. https://doi.org/10.1016/j.exer.2022.109101

13. Golden MI, Meyer JJ, Zeppieri M et al. Dry Eye Syndrome. 2024. In: StatPearls [Internet-resourse]. Treasure Island (FL): StatPearls Publishing; URL: https://www.researchgate.net/publication/380793871_Dry_Eye_Syndrome

14. Brzhevskiy VV, Somov EE. Rogovichno-kon’yunktival'ny kseroz (diagnostika, klinika, lechenie). S-Pb: Levsha. Sankt-Peterburg, 2003.- S. 5-12. In Russian

15. Mircheff AK. Lacrimal fluid and electrolyte secretion: a review. Curr Eye Res. 1989;8(6):607-17. https://doi.org/10.3109/02713688908995761

16. Mannis MJ, Holland EJ. Cornea: Fundamentals, Diagnosis and Management, 4th ed. New York: Elsevier, 2017.- P. 32

17. Tran CH, Routledge C, Miller J et al. Examination of murine tear film. Invest Ophthalmol Vis Sci. 2003;44:3520-3525. https://doi.org/10.1167/iovs.03-0178

18. McDonald JE. Surface phenomena of the tear film. Am J Ophthalmol. 1969;67:56-64. https://doi.org/10.1016/0002-9394(69)90008-7

19. Keill J. The anatomy of the human body, abridg'd: or, a short and full view of all the parts of the body. Together with their several uses drawn from their compositions and structures. London, 1747. P. 180. https://archive.org/details/bim_eighteenth-century_anatomy-of-the-humane-b_keill-james_1747/page/180/mode/2up?q=tears

20. Wolff E. The muco-cutaneous junction of the lidmargin and the distribution of the tear fluid. Trans Ophthalmol Soc UK. 1946;66:291–308

21. Cher I. Another way to think of tears: blood, sweat, and... «dacruon». Ocul Surf. 2007;5(3):251-254. https://doi.org/10.1016/s1542-0124(12)70615-8

22. Norn MS. Cytology of the precorneal film. Acta Ophthalmologica, 1960;38(2):67-71. https://doi.org/.1111/j.1755-3768.1960.tb00183.x

23. Ehlers N. The precorneal film. Biomicroscopical, histological and chemical investigations. Acta ophthalmol suppl. 1965; 81:19-34

24. Brauninger GE, Shah DO, Kaufman HE. Direct physical demonstration of oily layer on tear film surface. Am J Ophthalmol. 1972;73:132-134. https://doi.org/10.1016/0002-9394(72)90315-7

25. Holly FJ. Tear film physiology. Am J Optom Physiol Opt. 1980;57:252-257. https://doi.org/10.1097/00006324-198004000-00008

26. Zal'tsman M. Anatomiya i gistologiya chelovecheskogo glaza v normal'nom sostoyanii, ego razvitie i starenie.Izdatel'stvo Chikagskogo universiteta. 1912.-S.467. In Russian

27. Chen HB, Yamabayashi S, Ou B et al. Ultrastructural Studies on the Corneal Superficial Epithelium of Rats by in vivo Cryofixation with Freeze Substitution. Ophthalmic Research. 1995; 27(5), 286–295. https://doi.org/10.1159/000267738

28. Khomyakova NV. Osobennost' gistologicheskoy kartiny perednego epiteliya v kriostatnykh srezakh rogovitsy. Veterinariya i kormlenie. 2019;3:46-48. In Russian. https://doi.org/10.30917/ATT-VK-1814-9588-2019-3-14

29. Khomyakova NV. Mikroskopicheskoe issledovanie perednego epiteliya rogovitsy v eksperimente. Veterinariya i kormlenie. 2020;7:67-69. In Russian. https://doi.org/10.30917/ATT-VK-1814-9588-2020-7-18

30. Khomyakova NV. Struktura perednego epiteliya rogovitsy Sus scrofa domesticus pri kriofiksatsii. Morfologicheskie vedomosti. 2023;31(3):59-66. In Russian. https://doi.org/10.20340/mv-mn.2023.31(3).762

31. Camber O, Rehbinder C, Nikkila T et al. Morphology of the pig cornea in normal conditions and after incubation in a perfusion apparatus. Acta Vet Scand. 1987;28(2):127-134

32. Barros RC, Van Kooten TG, Veeregowda DH. Investigation of Friction-induced Damage to the Pig Cornea. Ocul Surf. 2015;13(4):315-320. https://doi.org/10.1016/j.jtos.2015.05.004

33. Abhari S, Eisenback M, Kaplan HJ et al. Anatomic Studies of the Miniature Swine Cornea. Anat Rec (Hoboken). 2018;301(11):1955-1967. https://doi.org/10.1002/ar.23890

34. Hammond GM, Young RD, Muir DD et al. The microanatomy of Bowman's layer in the cornea of the pig: Changes in collagen fibril architecture at the corneoscleral limbus. Eur J of Anat. 2020;24(5):399-406

35. Ehlers N. Morphology and histochemistry of the corneal epithelium of mammals. Cells Tissues Organs. 1970;75(2):161-198. https://doi.org/10.1159/000143448

36. Bülow N, Ehlers N. Morphology and dopa reaction of cultivated corneal epithelial cells. Acta Ophthalmologica. 2009;46(4):749-756. https://doi.org/10.1111/j.1755-3768.1968.tb02873.x

37. Podskochy A. Protective role of corneal epithelium against ultraviolet radiation damage. Acta Ophthalmol Scand. 2004;82(6):714-717. https://doi.org/10.1111/j.1600-0420.2004.00369.x7.

38. Podskochy A, Gan L, Fagerholm P. Apoptosis in UV-exposed Rabbit Corneas. Cornea. 2000;19(1):99–103. https://doi.org/10.1097/00003226-200001000-00019

39. Mallet JD, Dorr MM, Drigeard Desgarnier MC, et al. Faster DNA Repair of Ultraviolet-Induced Cyclobutane Pyrimidine Dimers and Lower Sensitivity to Apoptosis in Human Corneal Epithelial Cells than in Epidermal Keratinocytes. PLoS One. 2016;11(9):e0162212

40. Luchnikov EF, Abrosimov AJu. Gibel' kletki (apoptoz). Moskva: Meditsina; 2001.- 192s. In Russian