# Comparative morphological analysis of the zonular apparatus in porcine, feline, and canine species

## TL;DR

This study compares the zonular apparatus in pigs, cats, and dogs to find the best animal model for studying eye diseases like glaucoma.

## Contribution

The study identifies interspecies morphological differences in zonular structures relevant to angle-closure mechanisms.

## Key findings

- Pigs, cats, and dogs show distinct zonular fiber density, orientation, and insertion patterns.
- Canine eyes had the narrowest posterior vitreous zonule region compared to pigs and cats.
- SEM analysis revealed consistent vitreous zonule architecture across all species.

## Abstract

To characterize and compare the morphology of the zonular apparatus in pigs, cats, and dogs to identify the optimal animal model for studying zonular pathophysiology in angle-closure mechanisms.

Porcine (n = 15), feline (n = 8), and canine (n = 4) eyes were included in this descriptive, exploratory study. Slit-lamp biomicroscopy, photography, and histological staining (Hematoxylin and Eosin, Masson’s Trichrome) were utilized to evaluate structure and collagen distribution. The anterior segments of porcine, feline, and canine eyes were imaged ex vivo using ultrasound biomicroscopy (UBM). Ultrastructural morphology was further analyzed with scanning electron microscopy (SEM). Quantitative measurements were obtained with ImageJ and CaseViewer v2.4. This study is descriptive and that no inferential statistics were performed.

Significant interspecies differences were observed in zonular fiber density, orientation, and insertion patterns. The sagittal width of posterior vitreous zonule region was notably narrower than in humans (3–4 mm): approximately 0.56 mm in pigs, 0.40 mm in cats, and 0.30 mm in dogs. UBM imaging successfully detected vitreous zonules in porcine and feline eyes, but failed to visualize them in canine eyes. Dogs and cats exhibited similar zonular and ciliary body morphology; however, both species displayed leaf-shaped ciliary bodies and looser zonular arrangements compared to the more compact porcine configuration. Ultrastructural analysis using SEM identified consistent vitreous zonule architecture in all species.

Among the three species examined, unique zonular fiber origins and the ubiquitous vitreous zonules support the use of pigs or cats in studies of accommodation and glaucoma pathogenesis.