Breed-Specific Skull Morphology Reveals Insights into Canine Optic Chiasm Positioning and Orbital Structure through 3D CT Scan Analysis

Abstract

This study’s CT scan-based morphometric analysis of 50 adult dogs explored the relationship between skull shape variations (determined by the skull index, SI), optic chiasm, optic canals, and orbital shape. Dogs were classified as brachycephalic (SI ≥ 59), mesocephalic (SI ≥ 51 but <59), and dolichocephalic (SI < 51). No significant age or weight differences were observed. Skull lengths (brachycephalic: 11.39 ± 1.76 cm, mesocephalic: 15.00 ± 2.96 cm, dolichocephalic: 17.96 ± 3.44 cm) and facial lengths (brachycephalic: 3.63 ± 1.00 cm, mesocephalic: 6.46 ± 1.55 cm, dolichocephalic: 8.23 ± 1.03 cm) varied significantly, with shorter orbital depths (brachycephalic: 2.58 ± 0.42 cm, mesocephalic: 3.19 ± 0.65 cm, dolichocephalic: 3.61 ± 0.77 cm) in brachycephalic dogs. The optic chiasm-to-inion horizontal length ratio to cranial horizontal length positively correlated with the SI (r = 0.883, p < 0.001), while the ratio to neurocranial length showed no SI correlation (range: 55.5–75.0). Brachycephalic breeds had a significantly wider optic canal angle (93.74 ± 16.00°), along with broader lacrimal-zygomatic and zygomatic frontal process angles. These findings highlight the zygomatic bone’s role in influencing breed-specific orbital variations by connecting the face to the neurocranium, projecting the orbital rim outward and forward with facial shortening.

Foramina and canals of the skull base in Holstein cow: a computed tomography study

“…The results of the study show that the OC in Holstein cow is morphologically similar to humans and morphometrically higher than humans. Ichikawa et al [22] reported that the angle between the optic chiasma and the right-left lacrimal-zygomatic joint was 93.74° in brachycephalic dogs, 67.87° in mesocephalic dogs, and 61.05° in dolichocephalic dogs. In humans, Ten et al [47] reported the angle between OC and median plane as 39.3°, Berlis et al [4] 39.1°, Cheng et al, [7] 45.3° (right), 44.2° (left), Zhang et al…”

“…The area of JF was determined in the dry skull of bison, macaque, dog, fox and rat [51], and the area of HC was determined in the same species and rabbit [50]. Using CT images, the localization of the chiasmatic sulcus (sulcus chiasmatis), its angle with some bone points [22], and the volume of the JF were determined in the dog [43], and the diameter of the trigeminal nerve canal and OF and the distances between the foramina were measured in the rabbit [20].…”