# Comparative Histology of the Cornea and Palisades of Vogt in Various Non-Human Primates

## TL;DR

This study compares the corneal structure in non-human primates, showing how species differ in eye anatomy due to environmental and evolutionary factors.

## Contribution

The study provides a detailed comparative histology of the cornea and palisades of Vogt in 18 non-human primate species.

## Key findings

- Species-specific differences in corneal architecture are influenced by environmental and phylogenetic factors.
- The presence or absence of Bowman’s layer and variations in corneal stroma and limbal structures were observed across species.
- Well-defined palisades of Vogt were found in certain species, indicating potential differences in corneal stem cell niches.

## Abstract

The cornea is the most external and transparent structure of the eye influenced directly by the life conditions existing in the external environment. It plays an important role both in eye defense and light reception by the sense of vision. The study describes the microstructure of the cornea in non-human primates. The number of analyzed structures was 73, coming from 18 animal species. The histological staining visualized the subsequent structures of the cornea and allowed for the structural identification and description. The differences observed in the cornea architecture, such as the thickness of the corneal epithelium, the presence of corneal membranes and corneal stroma, together with the variability of the corneal limbus morphology, proved the importance of both environmental and phylogenetic factors in the architecture of the studied organ. Animal adaptation to the lifestyle in a specific environment seems to be crucial for the explanation of differences between species. The achieved results can be important for better understanding of the eye’s morphology, physiology and pathology, which is helpful for further studies.

The cornea is essential for proper ocular function, yet its histological structure varies considerably among animal species. Of particular importance are the palisades of Vogt in the limbal region, as they serve as a niche for limbal epithelial stem cells involved in corneal epithelial regeneration. This study was conducted on 73 eyeballs collected from 18 species of non-human primates originating from the Wrocław Zoological Garden (Poland). Eyeballs were fixed, processed, and embedded in paraffin. Four-micrometer sections were stained with Mayer’s H&E and PAS. Microscopically, the cornea showed either a four-layered pattern (anterior corneal epithelium, corneal stroma, Descemet’s membrane, posterior corneal epithelium) or a five-layered pattern when Bowman’s layer was present. A four-layered cornea occurred in the ring-tailed lemur, gray mouse lemur, Guianan squirrel monkey, Angolan colobus, and L’Hoest’s monkey, while the remaining species showed a five-layered structure with Bowman’s layer. The anterior corneal epithelium varied between species in thickness and number of cell layers (central region: 2–3 to 10–15 layers; 11.81 ± 0.43 µm to 44.23 ± 0.69 µm; peripheral region: 4–5 to 9–11 layers; 8.63 ± 2.57 µm to 42.45 ± 8.61 µm). Bowman’s layer ranged from 1.18 ± 0.01 µm to 3.22 ± 0.05 µm. The corneal stroma thickness differed markedly (237.96 ± 9.64 µm to 1438.29 ± 16.38 µm), as did Descemet’s membrane (4.92 ± 0.20 µm to 43.45 ± 0.49 µm), along with PAS reaction intensity. In the limbus, palisades of Vogt ranged from weakly to clearly developed; well-defined crypt-like structures were observed in the red-bellied lemur, red ruffed lemur, black-and-white ruffed lemur, Guianan squirrel monkey, L’Hoest’s monkey, Celebes crested macaque, and yellow baboon. The limbal epithelium also varied in thickness (5–6 to 15–17 cell layers). These results confirm distinct species-specific differences in corneal and limbal morphology that may reflect ecological conditions and functional adaptation. The presented data provides a comparative reference for veterinary ophthalmology and for studies on corneal epithelial regeneration involving limbal stem cells.