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

Van cats show a small but statistically significant morning IOP elevation; CCT and OST remain stable throughout the day.

This prospective observational study evaluated diurnal variation in intraocular pressure (IOP), central corneal thickness (CCT), and ocular surface temperature (OST) in 32 clinically healthy Van cats. Measurements were obtained in the morning and afternoon using standardized paired assessments, with statistical analysis via paired t-tests and effect sizes calculated using Cohen's d. Morning IOP (25.22 ± 6.44 mmHg) was statistically significantly higher than afternoon IOP (23.31 ± 6.50 mmHg), with a mean difference of 1.91 mmHg (95% CI: 0.24–3.57 mmHg; p = 0.025); however, the effect size was small (Cohen's d = 0.29), suggesting limited clinical relevance. CCT did not differ significantly between time points (655.34 ± 71.10 μm vs. 648.33 ± 61.22 μm; p = 0.154), nor did OST (35.90°C vs. 35.96°C; p = 0.603), with negligible to small effect sizes for both parameters. These findings establish breed-specific baseline ocular data for Van cats and suggest that, while a statistically detectable morning peak in IOP exists, the magnitude of fluctuation is small. Clinicians should be aware of this diurnal trend when interpreting IOP measurements obtained at different times of day, particularly when monitoring for glaucoma or ocular hypertension. CCT and OST appear stable across the day, making time of measurement less critical for these parameters in this breed.

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