Relationship between the daily intraocular pressure curve and serum cortisol levels in adult Shih Tzus

ABSTRACT: This study evaluated the intraocular pressure (IOP) of Shih Tzu dogs for 24 hours to prepare the daily intraocular pressure curve (DPC) and the mini-curve, in addition to analyzing the circulating cortisol values at different times and verifying the relationship with IOP. IOP was evaluated in 12 adult Shih Tzus using the TonoVet® from triple measurements in each eye every hour for 24 hours. Subsequently, blood samples were collected every three hours to assess cortisol levels throughout the period. The animals were kept under natural photoperiod and restraint prioritized minimal handling. The IOP and cortisol values found were statistically analyzed. The mean IOP found among all measurements was 15.61 ± 1.29 mmHg, with variations from 14.51 to 16.86 mmHg for 24 hours. Individual analysis of the data from the left (LE) and right eyes (RE) showed no statistically significant difference between the two eyes (P = 0.480), with mean IOP values of 15.74 ± 2.33 mmHg and 15.49 ± 2.22 mmHg, respectively. The obtained DPC showed that the IOPs measured during the final period of darkness tended to be lower than the IOPs measured between sunrise and the beginning of darkness (photophase). Although, the highest IOP peak occurred at 18:00 and the lowest at 4:00, a second maximum peak was observed at 8:00 and a second minimum peak at 6:00. The moments that encompass the maximum and minimum IOP values were considered when determining the ideal times to perform IOP measurements during the mini-curve. IOP pressure peaks did not follow cortisol levels at the same time points. The correlation between the overall mean IOP and cortisol, considering the 96 performed measurements, was not significant (r = 0.305, P = 0.462). Therefore, this study determined the values of the 24-hour intraocular pressure curve in adult Shih Tzu dogs, with minimum peaks occurring at 4:00 and 6:00, and maximum peaks at 8:00 and 18:00. However, no relationship between IOP and serum cortisol levels was observed.