Light and Electron Microscopic Study on Optic Nerve Head and Optic Nerve of Pig (Sus scrofa domesticus)

Abstract

The optic nerve head represents a critical structure in clinical ophthalmology, being the only part of the central nervous system that can be visualised non-invasively. Animal models are essential for advancing understanding of optic nerve pathology, particularly in glaucoma research. While non-human primates provide close anatomical similarity to humans, their use is limited by ethical concerns, availability, and handling difficulties. Rodents, though accessible, possess either rudimentary or weak laminar structures, restricting their suitability. In contrast, pigs offer a more economical, accessible, and practical alternative for comparative studies. The present investigation was conducted on twelve adult pigs of a local mixed breed to examine the light and electron microscopic morphology of the optic nerve head. Histological analysis revealed that the retinal portion of the optic nerve lacked photoreceptor, bipolar, and ganglion cells, with termination of the retinal pigmented epithelium before Bruch’s membrane. Retinal vasculature was observed centrally, oriented towards the vitreous. The choroidal portion exhibited thickened connective tissue boundaries between nerve bundles. The lamina cribrosa comprised elastic and reticular fibres, fibrocytes, and elongated melanocytes. Transmission electron microscopy demonstrated that optic nerve fibres became myelinated immediately after crossing the lamina cribrosa, with axoplasm densely packed with neurofilaments. These findings highlight the pig as a promising model for optic nerve research.