Progesterone is inversely associated with optic nerve sheath diameter in dogs: a cross-sectional analysis

Optic nerve sheath diameter (ONSD) is increasingly used as a non-invasive indicator of intracranial pressure and neurological status in both human and veterinary medicine, although physiological factors affecting ONSD measurements in dogs remain insufficiently defined. This study investigated the relationships among body mass (BM), age, serum estradiol (E2) and progesterone (P4) levels, and ultrasonographically measured ONSD in clinically healthy female dogs. Thirty-four female dogs of different ages and BM presented for routine clinical examination were included. ONSD was measured ultrasonographically via a transorbital approach using a microconvex probe, and the mean value of bilateral measurements was used for analysis. Serum E2 and P4 concentrations were determined using ELISA. Correlation analyses (Pearson or Spearman, depending on distribution) and power-law regression models were applied to evaluate associations between variables. Age and E2 were expressed as median (IQR) values [2.5 (1) years and 90.43 (85.03)], whereas BM, P4, and ONSD were reported as mean ± SD (23.15 ± 9.72 kg, 9.04 ± 1.96 ng/mL, and 2.42 ± 0.44 mm, respectively). A moderate negative correlation was observed between P4 and ONSD (r = - 0.41, p < 0.05), while no significant relationships were detected between age, BM, E2, and ONSD (p > 0.05). These findings suggest that P4 may show a modest inverse association with ONSD in clinically healthy female dogs, whereas BM, age, and E2 appear to have minimal influence. Further studies with larger populations are warranted to confirm these findings.