Anatomical Study and CT Scan of the Scleral Ring in the Little Owl ( <i>Athene noctua</i> )

Athene noctua, commonly known as the little owl, thrives across the warmer climates of Europe, Asia and North Africa. One of the anatomical features of birds is the presence of a bony scleral ring in the eye. In avians, this configuration comprises ossicles that are affixed together in diminutive plates and are not articulated to other components of the skeleton. The morphology, number, development and location of the scleral ring vary among different vertebrate groups. The objective of this research is to furnish a comprehensive elucidation of the morphology of the scleral ring in the A. noctua predicated on CT scan results and anatomical examination. The overall shape of the scleral ring, the number and shape of the ossicles and their positioning and extensions are notable features that can be used for classification purposes. The study population comprised 10 adult owls (five male and five female). Micro-CT scan, CT scan, ultrasound, radiography and morphometric analysis were used for these owls. The results indicated that the scleral ring in the owls consisted of 15 ossicles, arranged in quadrilateral and rectangular shapes. In one sample, the right eye ring of the owl contained 16 ossicles, which was considered an exceptional feature. The ring consisted of two parts: an anterior tubular section and a posterior conical section. Morphometric analysis showed significant differences between male and female owls in various measurements. SUMMARY: Ossicle Composition: The scleral ring in Athene noctua predominantly consists of 15 quadrilateral ossicles, with a rare anatomical variation of 16 ossicles observed unilaterally in one specimen. Structural Morphology: The ring displays a distinct bipartite architecture, featuring an anterior tubular segment with a near-circular cross-section and a posterior funnel-shaped segment with oval cross-section. Sexual Dimorphism: Morphometric analysis revealed statistically significant (p < 0.05) larger ocular dimensions in female specimens compared to males most measured parameters. Absence of Sesamoid Bone: Unlike other strigiform species, no sesamoid ossification or tubercular structures were observed adjacent to the scleral ring. Taxonomic and Clinical Relevance: These findings provide (1) diagnostic markers for ocular trauma assessment and (2) potential phylogenetic discriminators within Strigiformes.