Morphological analysis of the eye of Eudocimus ruber (Linnaeus, 1758)

Eudocimus ruber (Linnaeus, 1758), commonly known as the scarlet ibis, is a wading bird widely distributed throughout northern South America and along the Brazilian coast. However, detailed information on the ocular morphology of this species remains limited. Therefore, this study aimed to perform a multimodal morphological characterization of the eye and its associated structures in E. ruber. Eight specimens were used, and the heads were subjected to radiographic and computed tomographic examinations, followed by gross anatomical dissection, three-dimensional reconstruction, histological processing, and scanning electron microscopy. Gross anatomy revealed laterally positioned, flat-shaped eyes, eight extraocular muscles, a well-developed Harderian gland, and a pleated pecten oculi. Radiographic, tomographic, and three-dimensional analyses enabled visualization of the scleral ring and its anatomical position within the orbit. Histological examination identified the fibrous, vascular, and retinal tunics, including the scleral ossicles, scleral cartilage, ciliary body, iris, 10-layered retina, annular pad, pleated pecten oculi, Harderian gland, eyelids, and third eyelid. The scleral ossicles followed the type A overlap pattern according to the Lemmrich convention. The ocular morphology of E. ruber was generally consistent with that described in other avian species, with interspecific variation observed in several anatomical features. These findings expand the available anatomical knowledge of Threskiornithidae and provide a basis for future comparative studies of avian ocular morphology.