Microscopic Study of Bulbus oculi in Aleppo (Damascus) goat Estudio microscópico del Bulbus oculi en cabras de Alepo (Damasco) Reşit Uğran 1* , Serap İlhan Aksu 2 , Dilem Gülece Ermutlu 2 ¹ Batman University, Vocaonal School of Technical Sciences, Department of Veterinary Medicine. Batman, Turkey ² Kaas University, Faculty of Veterinary Medicine, Department of Histology and Embryology, Kars, Turkey *Corresponding author: resit.ugran@batman.edu.tr Revista Cienfica, FCV-LUZ / Vol. XXXV Recibido: 03/07/2025 Aceptado: 19/09/2025 Publicado: 31/10/2025 UNIVERSIDAD DEL ZULIA Serbiluz Sistema de Servicios Bibliotecarios y de Información Biblioteca Digital Repositorio Académico 1 of 5 Revista Cienfica, FCV-LUZ / Vol. XXXV https://doi.org/10.52973/rcfcv-e35738 UNIVERSIDAD DEL ZULIA Serbiluz Sistema de Servicios Bibliotecarios y de Información Biblioteca Digital Repositorio Académico ABSTRACT The eye is one of the most complex and essenal sensory organs, responsible for perceiving environmental smuli. This study aimed to histologically examine the eye structure of the Aleppo (Damascus) goat (Capra hiscus), a breed widely raised in the Eastern Mediterranean and Southeastern Anatolia regions for milk and meat producon. Twenty eyeballs (bulbus oculi) were collected from 10 adult goats (5 males and 5 females) and processed using standard histological methods. The examinaon revealed the presence of the three main ocular tunics: the fibrous tunic (sclera and cornea), the vascular tunic (choroid, ciliary body, and iris), and the nervous tunic (rena). The sclera consisted of three layers episcera, substana propria, and lamina fusca, with abundant collagen fibers and melanocytes. The cornea was characterized by a non-keranized strafied squamous epithelium, Bowman’s layer, collagenous stroma, Descemet’s membrane, and an endothelium. Schlemm’s canal and trabecular meshwork were idenfied at the sclerocorneal juncon. The choroid contained five disnct layers, including a tapetum fibrosum composed of organized collagen bundles but lacking melanocytes. The ciliary body and iris exhibited a bilayered epithelium and well- developed smooth muscle structures. The rena consisted of ten layers, consistent with other mammalian species, and no significant histological differences were observed between male and female goats. This study provides a foundaonal histological reference for the Aleppo goat eye and may contribute to future clinical and experimental studies involving ocular health and comparave anatomy. Keywords: Aleppo (Damascus) goat; eye; histology; histochemistry RESUMEN El ojo es uno de los órganos sensoriales más complejos y esenciales, responsable de percibir esmulos del entorno. Este estudio tuvo como objevo examinar histológicamente la estructura ocular de la cabra (Capra hiscus) de Alepo (Damasco), una raza ampliamente criada en las regiones del Mediterráneo Oriental y el Sureste de Anatolia para la producción de leche y carne. Se recolectaron veinte bulbos oculares (bulbus oculi) de 10 cabras adultas (5 machos y 5 hembras) y se procesaron ulizando métodos histológicos estándar. El examen reveló la presencia de las tres túnicas principales del ojo, la túnica fibrosa (escleróca y córnea), la túnica vascular (coroides, cuerpo ciliar e iris) y la túnica nerviosa (rena). La escleróca estaba compuesta por tres capas, epiescleróca, substana propria y lámina fusca, con abundantes fibras de colágeno y melanocitos. La córnea se caracterizaba por un epitelio escamoso estraficado no queranizado, la capa de Bowman, un estroma colagenoso, la membrana de Descemet y un endotelio. Notablemente, en la unión esclerocornea se idenficaron el canal de Schlemm y la malla trabecular. La coroides contenía cinco capas disntas, incluyendo un tapetum fibrosum compuesto por haces de colágeno organizados pero sin melanocitos. El cuerpo ciliar y el iris mostraron un epitelio bicapa y estructuras musculares lisas bien desarrolladas. La rena estaba compuesta por diez capas, consistentes con las de otras especies de mamíferos, y no se observaron diferencias histológicas significavas entre cabras machos y hembras. Este estudio proporciona una referencia histológica fundamental sobre el ojo de la cabra de Alepo y puede contribuir a futuros estudios clínicos y experimentales relacionados con la salud ocular y la anatomía comparada. Palabras clave: Cabra de Alepo (Damasco); ojo; histología; histoquímica

Revista Cienfica, FCV-LUZ / Vol. XXXV UNIVERSIDAD DEL ZULIA Serbiluz Sistema de Servicios Bibliotecarios y de Información Biblioteca Digital Repositorio Académico 2 of 5 INTRODUCTION The eye is one of the most essenal sensory organs, which is crical in enabling communicaon between living organisms and their environments [1]. Structurally, the visual system comprises the opc nerve, the eyeball (bulbus oculi), and the accessory ocular structures (organa oculi accessoria), making it one of the most complex sensory systems in the body. These components are highly sensive to light, environmental smuli, and various diseases [2 ,3]. A histological understanding of the neuroectoderm derived structures and ectodermal layers of the eye is essenal for elucidang disease pathophysiology and for the development of targeted therapeuc approaches. Anatomically, the eye is composed of mulple overlapping ssue layers. The external structures include the eyelids, ocular muscles, accessory glands, conjuncva, and eyelashes. Internally, the eye consists of three concentrically arranged layers: the outer fibrous layer (sclera and cornea), the middle vascular layer or uvea (comprising the iris, ciliary body, and choroid), and the innermost neural layer the rena. Each of these layers has disnct histological characteriscs and can be further subdivided [4 ,5]. The Aleppo goat (Capra hiscus) originally bred in Damascus, Syria, is among the most prolific goat breeds and is valued in several Middle Eastern countries for both milk and meat producon [6 ,7]. Aleppo goats typically have long hair and range in color from reddish and dark chestnut to brown, oſten with white markings. Characterized by a ram-like head and long, pointed ears, adult males weigh between 70–90 kg, while females typically weigh between 55–60 kg [8]. In Turkey, they are predominantly raised in the Eastern Mediterranean and Southeastern Anatolia regions [9 , 10]. Previous literature has primarily focused on the gross anatomy, histology, and pathology of ocular ssues across various animal models [3 , 11 , 12 , 13 , 14 , 15 , 16 , 17]. The present study aims to contribute to scienfic fields ulizing animal-human experimental models by providing histological data on the Aleppo goat eye, which may serve as a foundaon for future clinical and experimental research. MATERİALS AND METHODS Ethical approval This study was approved by the Kaas University Local Eth- ics Commiee for Animal Experiments (KAU-HADYEK) under De- cision No: 2024/168. Animals A total of 20 eyeballs (bulbus oculi) obtained from adult Aleppo goats (n = 10 males and n = 10 females) were ulized in this study. 10 eye ssues from male and female goats were used, so that each animal had 2 eyeballs. Histological technique Following dissecon, the eye ssues were fixed in 10% neutral buffered formalin for histological evaluaon. The samples were processed using a standard histological protocol: dehydraon through a graded ethanol series (70%, 80%, 90%, and absolute alcohol, three changes each), clearing in xylene (three changes), and embedding in paraffin. Serial secons of 6 μm thickness were cut using a microtome (Leica RM2125 RTS, Germany). The ssue secons were stained with Crossman’s modified triple staining method. Microscopic examinaon was performed using a BX51 light microscope (Olympus, Japan) and was photographed (DP72 Olympos, Japan). RESULTS AND DISCUSSIONS The ssues study of the eyes of Aleppo goats revealed the presence of three disnct tunics. These were: the outer fibrous layer (comprising the sclera and cornea, or tunica fibrosa bulbi), the vascular layer (consisng of the choroid, ciliary body, and iris, or tunica vasculosa bulbi), and the inner neural layer (tunica interna bulbi), which includes the rena. Within the sclerocorneal coat, forming the outer or fibrous layer, both scleral and corneal structures were observed. In both male and female goats, the sclera was composed of three layers: the episclera, the substana propria, and the lamina fusca. The scleral stroma consisted predominantly of thick collagen fibers, among which vascular structures and nerve fibers were noted. In the lamina fusca, adjacent to the choroid, thinner collagen bundles were present, along with melanocytes (FIGS. 1 A, B). The tenon space, also known as the episcleral space, was visible between the scleral substana propria and the episclera. The cornea, the transparent frontal window of the eye, exhibited a strafied, non-keranized squamous epithelium anteriorly, a stroma composed of parallel collagen lamellae centrally, and a posterior single-layered non-keranized squamous epithelium. At the sclerocorneal juncon, the Schlemm’s canal and Fontana spaces (trabecular meshwork) were idenfied. The tunica fibrosa bulbi (sclera and cornea) constutes the outermost layer of the eye. In mammals, the sclera is primarily composed of dense connecve ssue, though in some vertebrates (e.g., geese, ducks), it may also include carlage or bone [18 , 19]. In Aleppo goats, the sclera was histologically composed of three layers episclera, stroma (substana propria), and lamina fusca similar to other mammalian species [20 , 21]. These layers contained collagen fibers, and melanocytes and nerve endings were also observed in some areas. Previous studies have indicated the presence of smooth muscle bundles within the scleral layers of cale (Bos taurus), buffalo (Bubalus bubalis), donkeys (Equus asinus), and goats (Capra hircus) [22], which is consistent with our findings, as smooth muscle bundles were detected in the episcleral layer of Aleppo goats. The choroid, which contains a dense concentraon of pigment cells, was found to be composed of five disnct layers: the lamina supracoroidea, lamina vasculosa, tapetum fibrosum, lamina choriocapillaris, and lamina basalis (Bruch’s membrane). The tapetum fibrosum contained numerous fibroblasts and large collagen bundles (FIGS. 1 C, D).

Histological Invesgaon of Bulbus Oculi Aleppo goat / Uğran et al. UNIVERSIDAD DEL ZULIA Serbiluz Sistema de Servicios Bibliotecarios y de Información Biblioteca Digital Repositorio Académico FIGURE 1. Histological features of sclera and choroid in male and female Aleppo goats. A: Female Aleppo goat’s sclera, B: Male Aleppo goat’s sclera, C: Female Aleppo goat’s choroid, D: Male Aleppo goat’s choroid, Bv: Blood vessel, Ch: Choroid, Ep: Episclera, Lf: Lamina fusca, m: muscle bundle, Sp: Substana propria, T: Tapetum fibrosum, Triple staining. In the tunica vasculosa bulbi, between the iris and the choroid, the corpus ciliare and processus ciliaris were lined by a bilayered cuboidal epithelium. Numerous melanocytes, nerve plexuses, blood vessels, as well as well-developed dilator and sphincter muscle fibers, were observed within the iris, which represents the anterior connuaon of the corpus ciliare (FIG. 2). The cornea is a transparent, avascular structure with a dense neural network that protects the eye against external trauma and foreign bodies. It has been described in numerous mammalian species, including donkeys (Equus asinus), horses (Equus caballus), ruminants (domesc and wild) (Ruminana), rodents (Rodena), marine mammals (Cetacea and Pinnipedia), herbivores (Herbivora), pigs (Sus scrofa domescus), bears (Ursidae), and primates (Primates). In mammals, the cornea is composed of mulple layers: strafied non-keranized squamous epithelium at the surface, followed by the Bowman’s membrane, stromal layer, Descemet’s membrane, and the innermost endothelium [23], 24 , 25 , 20 , 21 , 12]. Although earlier studies suggested that the Bowman’s membrane is found only in primates (Primates) [26], later research has demonstrated its presence in various other mammals, such as pigs (Sus scrofa domescus), cale (Bos taurus), deer (Cervidae), bears (Ursidae), sheep (Ovis aries), and dogs (Canis lupus familiaris) [27 , 28 , 29 , 30 , 31]. In this study, the cornea of Aleppo goats exhibited a structure consistent with other mammals: a regular epithelial layer, a thin Bowman’s membrane, a dense collagenous stroma, Descemet’s membrane, and an endothelium. Addionally, the presence of Schlemm’s canal and the trabecular meshwork (Fontana’s spaces) at the corneoscleral juncon was confirmed. FIGURE 2. Histological features of corpus ciliare and iris in male and female Aleppo goats. A: Female Aleppo goat’s corpus ciliare, B: Male Aleppo goat’s corpus ciliare, C: Female Aleppo goat’s iris, D: Male Aleppo goat’s iris, Bv: Blood vessel, C-S: Cornea-scleral area, I: Iris, Cc: Corpus ciliare, Cp: Ciliary processus, dm: dilator muscle, nPe: Non-pigmented epithelium, Pe: Pigmented-epithelium. Triple staining. The rena, or tunica interna bulbi, consisted of ten layers arranged from the outer to the inner surface: the pigment epithelium (adjacent to the choroid), rods and cones layer, outer liming membrane, outer nuclear layer, outer plexiform layer, inner nuclear layer, inner plexiform layer, ganglion cell layer, nerve fiber layer, and the inner liming membrane (FIG. 3). In most domesc mammals, the choroid is divided into five layers: lamina supracoroidea, vascular layer, tapetal layer, choriocapillary layer, and Bruch’s membrane [32 , 33 , 34]. The tapetum is present in both vertebrates and invertebrates and is located within the choroid or deep layers of the rena in vertebrates. Structurally, the tapetum is categorized into two types: tapetum cellulosum (cellular) and tapetum fibrosum (acellular). Tapetum fibrosum, which was observed in this study, consists of ghtly packed collagen fibers and lacks cellular components [35]. It has been reported that the tapetum lucidum is absent in primates (Primates), pigs (Sus scrofa domescus), birds (Aves), and squirrels (Sciuridae), but is present in reples (Replia), fish (Pisces), dogs (Canis lupus familiaris), bats (Chiroptera), cale (Bos taurus), cats (Felis catus), sheep (Ovis aries), crocodiles (Crocodylidae), goats (Capra hircus), lemurs (Lemuroidea), and ferrets (Mustela putorius furo) [3 , 12 , 15 , 36 , 37 , 38]. In the examined samples, the choroid of Aleppo goats was observed to be rich in melanocytes and blood vessels, whereas the tapetum fibrosum was composed of regularly arranged collagen bundles and contained no melanocytes. The bilayered epithelial structure of the corpus ciliare and processus ciliaris in Aleppo goats pigmented internally and non- pigmented externally was similar to that observed in camels (Camelus dromedarius) [37], bears (Ursidae) [12 , 21], sheep (Ovis aries) [15], and goats (Capra hircus) [16]. Similarly, in the iris stroma, a rich vascular network, dilator and sphincter muscles, dense connecve ssue, and nerve fibers were idenfied. The dilator and sphincter muscles were well-developed in Aleppo goats. 3 of 5

Revista Cienfica, FCV-LUZ / Vol. XXXV UNIVERSIDAD DEL ZULIA Serbiluz Sistema de Servicios Bibliotecarios y de Información Biblioteca Digital Repositorio Académico FIGURE 3. Histological features of corpus rena in male and female Aleppo goats. A: Female Aleppo goat’s rena, B: Female Aleppo goat’s rena, Bv: Blood vessel, Ch: Choroid, R: Re- na, Triple staining. Histologically, the rena of Aleppo goats was composed of ten disnct layers, similar to other mammalian species [3 , 12 , 15 , 16 , 38 , 39]. No histological differences were observed between male and female specimens. CONCLUSION This histological invesgaon of the Aleppo goat eye is sig- nificant not only because it represents the first such study on this specific breed but also due to its contribuon to idenfying species-specific characteriscs. These findings provide valuable foundaonal knowledge for future clinical and comparave re- search, parcularly in the fields of veterinary ophthalmology, histology, and experimental animal models. Conflict of interest The authors declare that they have no conflict of interest. BIBLIOGRAPHIC REFERENCES [1] Eurell JA, Frappier BL. Dellmann’s textbook of Veterinary histology. 6th. ed. Ames, USA: Blackwell Publishing; 2006. [2] Akın F, Samsar E. Göz hastalıkları. 2nd. Ed. Ankara: Medipres; 2005. [3] Soliman SM, Adam ZAA, Abd Allah UKM. Light and electron microscopic structure of goat’s rena. J. Vet. Med. Res. [Internet]. 2010; 20(1):52-62. doi: hps://doi. org/p8mp [4] Junqueira LC, Carneiro J. Basic histology. 10th. ed. New York: McGraw-Hill; 2003. [5] Nilsson DE. Eye evoluon and its funconal basis. Vis. Neurosci. [Internet]. 2013; 30(1-2):5-20. doi: hps://doi. org/f24mdf [6] Mavrogenis AP, Constannou A, Louca A. Environmental and genec causes of variaon in producon traits of Damascus goats. 1. Pre-weaning and post-weaning growth. Anim. Sci. [Internet]. 1984; 38(1):91-97. doi:hps://doi.org/bzmjd8 [7] Economides S, Georghiades E, Koumas A, Hadjipanayiotou M. The effect of cereal processing on the lactaon performance of Chios sheep and Damascus goats and the pre-weaning growth of their offspring. Anim. Feed Sci. Technol. [Internet]. 1989; 26(1-2):93-104. doi: hps:// doi.org/crjktn [8] Constannou A. Genec and environmental relaonships of body weight, milk yield and lier size in Damascus goats. Small Rumin. Res. [Internet]. 1989; 2(2):163-174. doi: hps://doi.org/dsv4dn [9] Yalçın BC. Sheep and goats in Turkey. Rome: FAO; 1986 [cited 22 May 2025]. Available in: hps://goo.su/ UdfNUVf [10] Keskin M. Hatay Bölgesinde Yoğun Yeşrme Koşullarında Şam (Damascus) Keçilerinin Morfolojik Özellikleri ve Performanslarının Saptanması [Doctoral thesis on the Internet]. Hatay: Mustafa Kemal Üniversitesi. 2000 [cited 22 May 2025] 103 p. Available in: hps://goo.su/alRz8sT [11] Ohuchi H, Sato K, Habuta M, Fujita H, Bando T. Congenital eye anomalies: more mosaic than thought?. Congenital Anomalies. [Internet]. 2019; 59(3):56-73. doi: hps:// doi.org/p8mq [12] Kirbaş-Doğan G, Koral-Taşçı S, Dalga S, İlhan-Aksu S. Anatomical and histological studies on the eyes of brown bear (Ursus arctos horribilis). Turk. J. Vet. Anim. Sci. [Internet]. 2020; 44(4):871–878. doi: hps://doi.org/ p8mr [13] Okşar D, Orhan İ, Alan A, Köse F, Düzler A. Anatomical study of bulbus oculi in Akkaraman sheep. Erciyes Üniv. Vet. Fak. Derg. [Internet]. 2021; 18(3):145–151. doi: hps://doi.org/p8ms [14] Jabbar AI, Ibrahim RS. Dıssector And Morphometrıc Study Of The Buffaloes Eyeballs (Bubalus Bubulıs). Biochem. Cell. Archiv. [Internet]. 2021 [cited Apr 23 2025]; 21(2):4303-4308. Available in: hps://goo.su/KyiT [15] Dalga S, Aksu SI, Aslan K, Deprem T, Uğran R. Anatomical and histological structures of eye and lacrimal gland in Norduz andMorkaraman sheep. Turk. J. Vet. Anim. Sci. [Internet]. 2022; 46(2):336-346. doi: hps://doi.org/ p8mt [16] Dalga S, Aslan K, Taşçı SK, Ermutlu D, Aksu Sİ. Morphometric and Histological Structure of Bulbus Oculi in Goats. Acta Morphol. Anthropol. [Internet]. 2024; 31(1-2):94-108. doi: hps://doi.org/p8mw [17] Yılmaz C, Kabak M, Selviler-Sizer S. Comparave macroanatomical and scanning electron microscopy study of the eyeball in brachycephalic and mesocephalic dog breeds. Microsc. Res. Tech. [Internet]. 2024; 87(10):2408-2417. doi: hps://doi.org/p8mx [18] Öktay M. Comparave anatomy of vertebrate animals. İstanbul: İstanbul Üniversitesi Fen Fakültesi. [Internet]. 1998; p. 340–53. Turkish. [19] Ross N. Anatomy of domesc birds. Ankara: Medisan Publishing House; 2008. [20] Nickel R, Schummer A, Seiferle E, Wight PAL. The Anatomy of the Domesc Animals. Berlin: Springer; 2004. [21] Klećkowska-Nawrot JE, Goździewska-Harłajczuk K, Darska M, Barszcz K, Janeczek M. Microstructure of the 4 of 5

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