The human eyeball ciliary body is an analogue of the bony fishes swimming bladder gas gland

The role of the ciliary body as a gas gland in the formation of intraocular fluid has not been sufficiently studied. The aim of the work was to compare the morphology of the ciliary body of the human eyeball and the gas gland of the swim bladder of bony fish to establish their structural and functional analogy. The swimming bladders of bony fish, carp (Cyprinus carpio L., n=7) and pike-perch (Lucioperca lucioperca L., n=7) were studied. For the study, physiological saline, silver nitrate solution and 1% hydroquinone solution were injected through the caudal artery under supravital conditions. After that, the swimming bladders were removed, stretched on wax plates, fixed in 10% formalin and poured into paraffin blocks. Serial sections 4-5 μm thick were stained with hematoxylin and eosin according to Van Gieson, Weigert's iron hematoxylin, Mallory's, orcein and resorcinol. The study established that the swimming bladders of open-bladder fish (carp) exchange gases using the so-called "oval", while those of closed-bladder fish (pike-perch) use the "oval" and the gas gland. The "oval" is an oval-shaped formation located on the inner surface of the dorsal section of the swimming bladder of fish and is distinguished by blood vessels upon visual inspection. In the area of the gas gland, there is a dense cluster of blood vessels, from large arteries and veins to exchange micro-vessels, including capillaries. A large number of blood vessels participate in the formation of the "oval", in most cases these are micro-vessels, they are located in a thin plate over its entire area. The gas gland is formed by epithelial cells, entwined with numerous blood micro-vessels. The above-mentioned vascular structures of fish are similar to the vascular structures of the ciliary body of the human eyeball, the producer of intraocular fluid; they are formed according to the principle of countercurrent exchangers of the gas glands of the bladders of bony fish. Based on the data obtained, it can be concluded that the ciliary body of the human eyeball is an analogue of the gas gland of the swimming bladder of bony fish.