OBJECTIVE: To evaluate the effect of intravenous mannitol and hypertonic saline (HS) on intraocular pressure (IOP) and biometry parameters of horses with elevated intracranial pressure (ICP). PROCEDURES: Seven horses with normal ophthalmic exams were anesthetized and placed in lateral recumbency. A subarachnoid transducer was placed, and the head was lowered until ICP measured 40 mmHg +/- 2 mmHg. Five intravenous boluses of mannitol 20% (0.4 g/kg) or HS 7.2% (1 mL/kg) were administered, each 15 min apart. A 2-day washout period ensued, and the procedure was repeated with the other hyperosmotic agent. IOP via a TonoVet, axial length and vitreous chamber depth via biometry, and ICP via the subarachnoid transducer were monitored. RESULTS: No significant correlation between ICP and IOP was identified. Estimated marginal mean (EMM) reduction in IOP (comparing values 5 min post bolus to values at bolus administration) following mannitol and HS was 2.4 mmHg and 0.4 mmHg, respectively. Mean axial length EMM decreased by and increased by 0.1 mm following mannitol and HS, respectively. Mean vitreous chamber depth EMM was unchanged and increased by 0.1 mm following mannitol and HS, respectively. The EMM of the second HS bolus demonstrated an increase of 0.8 mm (95% confidence interval 0.01-1.5 mm) in axial length (p <
0.048), though the remaining individual bolus assessments were not statistically significant. CONCLUSIONS: Intravenous mannitol and HS did not cause a significant change in IOP, axial length, or vitreous chamber depth in healthy, anesthetized, laterally recumbent horses in this experimental model of increased ICP.