Comparison of computed tomographic ocular biometry in brachycephalic and non-brachycephalic cats

Abstract

Background and aim: Ocular biometry has been used to evaluate ocular parameters; however, several factors need to be considered. In humans, age and sex have been shown to affect ocular biometry. The main factor that affects feline ocular biometry is the head circumference. At present, several reports have revealed that canine ocular biometry differs among dog breeds. However, there are no reports on normal ocular biometry in cats using computed tomography (CT). Therefore, this study aimed to explore feline ocular parameters between brachycephalic (B) and non-brachycephalic (NB) cats using CT and to evaluate the influence of age or sex of cats on ocular biometry.

Materials and methods: Twenty-four normal cats were divided into two groups: B (n=12) and NB (n=12). Each group had an equal number of designated males and females. CT was performed under mechanical restraint without general anesthesia and intravenous contrast enhancement. Ocular biometry, dimensions of the internal structure, including attenuation numbers and extra-ocular structures, were evaluated and compared.

Results: B-cats had a significantly wider globe width (GW) than NB-cats (p<0.05). In addition, globe length (GL) and GW were significantly correlated with the age of the cats. Significant correlation between GL and age was observed in all cats (r=0.4867; p<0.05), NB-cats (r=0.8692; p<0.05), and B-cats (r=0.4367; p<0.05), whereas the correlation between GW and age was observed in B-cats only (r=0.7251; p<0.05). For extra-ocular structures, NB-cats had significantly greater orbital depth than B-cats (p<0.05), and orbital diameter was significantly correlated with age in all cats and B-cats (p<0.05).

Conclusion: CT can be used for ocular biometric evaluation in cats with different skull types. GW was wider in B-cats, whereas the orbital depth was greater in NB-cats. Moreover, GW, GL, and orbital diameter were affected by the age of the cats. This information will be useful for further ocular diagnosis and treatment, especially in prosthetic surgical procedures.

Keywords: age; biometry; cat; computed tomography; eye; skull.

Figure-1

Multiplanar reconstructed-computed tomographic images on each plane; dorsal plane (a), sagittal plane (b), axial plane (c), sagittal oblique to reveal the most depth of retrobulbar region (d) for measurement globe length (a and b), globe width (a and c), globe height (b and c), anterior chamber depth (a and b), lens thickness (a and b), vitreous chamber depth (a and b), orbital depth (d), orbital diameter (d), and retrobulbar depth (d).

Figure-2

Globe size in each dimension; globe length (a), globe height (b), globe width (c) and orbital depth (d) between non-brachycephalic (NB) and brachycephalic (B) cats. Globe width of the B cats was significantly wider than that of the NB cats and orbital depth of the NB cats was significantly deeper than that of the B cats.

Figure-3

The correlations between ocular structures and age; globe length and age in all cats (a), globe length and age in non-brachycephalic cats (b), globe length and age in brachycephalic cats (c), globe width and age in brachycephalic cats (d), orbital diameter and age in all cats (e), and orbital diameter and age in brachycephalic cats (f).