Magnetic resonance imaging of the normal feline eye using a T1-weighted volumetric sequence

This study aimed to characterise the normal magnetic resonance imaging (MRI) appearance of the feline eye and establish reference ranges.

Medical records of cats that underwent MRI of the head between 2022 and 2023 were reviewed. Patients with any ocular and/or orbital abnormalities were excluded. Measurements were performed from the T1-weighted volumetric sequence.

Forty-six cats (89 eyes) were included, with a mean age at presentation of 7.5 years. Domestic shorthair was overrepresented (82%). Median axial globe length was 2.13 cm and median equatorial globe width was 2.01 cm. Median anterior chamber depth and mean vitreous chamber depth were 0.47 and 0.79 cm (±0.05 cm), respectively. Median axial lens length was 0.86 cm and median equatorial lens width was 1.33 cm. The median width of the optic nerve was 0.16 cm and the mean width of the entire optic nerve sheath was 0.45 cm (±0.05 cm). Weak positive relationships were statistically noted between skull width and axial globe length, equatorial globe width and anterior chamber depth. No associations were found between all parameters and age, weight or sex.

Main limitations include retrospective nature, single observer and overrepresentation of domestic shorthair cats.

This study establishes normative values of feline ocular structures on T1-weighted volumetric MRI sequence. Some measurements of globe dimensions vary with skull size.