The effect of body position on intraocular pressure in anesthetized horses.

Abstract

OBJECTIVE: To evaluate the effect of four recumbent body positions on intraocular pressure (IOP) in anesthetized normal horses. ANIMALS STUDIED: Ten nonglaucomatous adult horses. PROCEDURES: Intraocular pressure was measured with a rebound tonometer in both eyes of standing sedated horses (baseline), then under general anesthesia during four randomized recumbent body positions, including Trendelenburg (Tr; 15-degree head down), reverse Trendelenburg (RTr; 15-degree head up), dorsal, and lateral; only the superior eye was measured in lateral positions. The mean of 3 IOP readings was taken at each position, allowing a minimum of 2&#xa0;minutes of acclimatization after each position change before obtaining measurements. Repeated Measures Analysis with Newman-Keuls Multiple Comparison Post hoc was used to compare IOPs in different positions, and linear regression was used to compare IOP with age and weight cofactors. RESULTS: When compared to baseline, the greatest change in IOP occurred in Tr (increase of 25.63&#xa0;&#xb1;&#xa0;8.12&#xa0;mm&#xa0;Hg). When comparing all recumbent positions to baseline, IOP significantly increased in 3 of 4 body positions (P&#xa0;<&#xa0;.001), with no significant difference identified between RTr and baseline. When comparing all body positions to each other, the greatest IOP difference occurred between the Tr and the RTr positions (increase of 26.95&#xa0;&#xb1;&#xa0;5.41&#xa0;mm&#xa0;Hg). Age and weight were not correlated with IOP in any position. CONCLUSIONS: Recumbent body position significantly increases IOP in normal eyes of horses under injectable anesthesia.