The retina of the collared peccary (Pecari tajacu): structure and function

Objective: To study retinal morphology and function in the collared peccary, an ungulate species distantly related to the domestic pig. Animal studies: Twenty captive peccaries anesthetized for routine health examinations. Procedures No abnormalities were noted on a complete ophthalmic examination. Fundi were examined ophthalmoscopically and photographed. The eyes of an individual that died of unrelated, nonocular reasons were studied histologically and by immunohistochemistry. Scotopic, mixed rod–cone, and photopic electroretinography (ERG) responses were recorded using the ‘QuickRetCheck’ (n = 6) and ‘Dog diagnostic’ (n = 5) protocols of the Handheld Multispecies ERG (HMsERG). Results: The fundus of the peccary is atapetal, with varying amounts of pigmentation seen ophthalmoscopically, and histologically in the retinal pigment epithelium (RPE) and choroid. The retina is holangiotic with dichotomously branching vessels. These cross, and apparently loop on, the optic disk surface, but no venous circle was seen. Immunohistochemistry suggests a high concentration of cone photoreceptors with red/green cones being more abundant than blue cones. Rod ERG responses were very low with no evident dark adaptation. Mixed rod–cone and cone ERG response amplitudes were low compared to those of domestic pigs, but quite similar to those of minipigs. Conclusions: To the best of our knowledge, this study describes the collared peccary's retinal features for the first time. A comparison of our findings with data from other ungulate species shows some similarities between the peccary and pig retinas. Further studies are warranted to determine whether the peccary can be used alongside the pig as an animal model in retinal studies.