Diurnal Variation of Intraocular Pressure, Central Corneal Thickness, and Ocular Surface Temperature in Van Cats

Objective: This study aimed to evaluate the presence of diurnal variation in intraocular pressure (IOP), central corneal thickness (CCT), and ocular surface temperature (OST) in clinically healthy Van cats. Animals: Thirty-two clinically healthy Van cats. Methods: IOP, CCT, and OST were measured in the morning and afternoon in all cats. Paired measurements were obtained from each animal to assess diurnal changes. Differences between morning and afternoon measurements were analyzed using paired t-tests. Effect sizes were calculated using Cohen's d. Results: Mean morning IOP (25.22 ± 6.44 mmHg) was significantly higher than afternoon IOP (23.31 ± 6.50 mmHg) (t(63) = −2.29, p = 0.025). The mean difference was 1.91 mmHg (95% CI: 0.24–3.57 mmHg), corresponding to a small effect size (Cohen's d = 0.29). CCT showed no significant difference between morning and afternoon measurements (655.34 ± 71.10 μm vs. 648.33 ± 61.22 μm; p = 0.154), with a small effect size (Cohen's d = 0.18). Similarly, OST did not differ significantly between time points (35.90°C ± 0.60°C vs. 35.96°C ± 0.50°C; p = 0.603), and the effect size was negligible (Cohen's d = 0.06). Conclusion and Clinical Relevance: Van cats exhibited a small diurnal variation in IOP, whereas CCT and OST remained stable throughout the day. The magnitude of IOP fluctuation was minimal and may not be clinically relevant. These findings provide baseline physiological data for ocular parameters in Van cats and may assist clinicians in interpreting ophthalmic measurements obtained at different times of the day.