Comparative analysis of ocular biometry, ocular protrusion, and palpebral fissure dimensions in brachycephalic and nonbrachycephalic dog breeds.

This study compared skull morphology and ocular parameters in brachycephalic (BC, n = 16) and nonbrachycephalic (NB, n = 16) dogs using head CT scans. The results of a Schirmer tear test I (STT I), intraocular pressure (IOP), ocular biometry, external structure, ocular protrusion, and palpebral fissure dimensions were evaluated and compared between BC and NB dogs. There were no statistically significant differences in the STT I results, IOP, globe dimensions, globe volume, internal structure, and external structure between BC and NB dogs (P > .05). Brachycephalic dogs exhibited significantly greater ocular protrusion and significantly larger palpebral fissure dimensions compared with NB dogs. For all dogs, we found a strong positive correlation between globe volume and body weight (r = 0.836, P = .0000). The globe volumes, external structure parameters, and ocular protrusion were normalized by body weight and were also significantly larger in BC dogs compared with NB dogs (P < .001). The ocular protrusion (r = 0.521, P < .0000) and horizontal palpebral fissure (r = 0.372, P = .0024) showed a moderate positive correlation with the cephalic index (CI). Additionally, normalized globe volume (r = 0.435, P = .0003), normalized orbital depth (r = 0.419, P = .0005), and normalized retrobulbar depth (r = 0.444, P = .0002) had a moderate positive correlation with the CI. The study emphasizes how the distinctive skull structure of BC dogs, with shortened facial bones and thickened retrobulbar soft tissue, influences their ocular appearance and raises the risk of eye problems.