Choroid and Retinal Pigmented Epithelium in Pigs: A Comprehensive Light and Ultrastructural Study

This study was conducted on 12 adult pigs of a local mixed breed to examine the histology, histochemistry and ultrastructure of the choroid and retinal pigmented epithelium (RPE). The tissues were fixed in Davidson's Fluid for light microscopy and Karnovsky's fluid for electron microscopy. Due to the physiological, anatomical and metabolic similarities between pigs and humans, pigs are a suitable animal model for various ophthalmic studies. Bruch's membrane exhibited five distinct layers: the basement membrane of the RPE, the inner collagenous layer, the elastic lamina, the outer collagenous layer and the basement membrane of the choriocapillaris. Age-related changes, such as vesicular formation, were also observed. Patches of collagen fibre lamellae were noted in the choroid stroma, indicating the presence of a vestigial tapetum. The apical part of the intercellular space of the RPE cells was completely sealed off by zonula occludens and zonula adherens. Hemidesmosomes were not present at the basal surface of the RPE cells. Numerous melanosomes, lipofuscin, mitochondria, phagolysosomes, melanolysosomal bodies, and both smooth and rough endoplasmic reticulum were observed in the granular cytoplasm of the RPE. Double-membrane-bound round vesicles were also observed in the RPE cytoplasm, characterised by a uniform intermembranous space and a central core space, potentially representing liposome-like structures, although this type of vesicle has not been previously described in the RPE. Overall, the study demonstrated that pigs have a choroid, Bruch's membrane and RPE morphology similar to that of humans, providing a valuable reference for studies using this animal model. Thus, pigs can be utilised as an experimental model for ophthalmic research.