Immobilization stress induces elevation of intraocular pressure in rabbits

The aim of this study was to test whether immobilization and intravenous volume load as stressors influence the intraocular pressure in rabbits. Rabbits were immobilized for 1 h in a horizontally placed plastic tube with an internal diameter of 13.2 cm and a length of 33.2 cm. After immobilization, rabbits received rapid intravenous drip infusion of 5% glucose solution, 20 ml/kg of body weight, in 5 min. The intraocular pressure immediately after immobilization (11.2 +/- 3.0 mm Hg; mean and standard deviation) was significantly higher compared to control rabbits without immobilization (9.2 +/- 1.0 mm Hg, Student's t test, p = 0.0462). This difference became significantly larger when volume load was exerted on both groups of rabbits (22.7 +/- 5.6 versus 16.4 +/- 2.2 mm Hg, p = 0.0067). Serum levels of cortisol, adrenaline, and noradrenaline were significantly elevated after immobilization (p = 0.0002, p = 0.0271, p = 0.0296, respectively). Venous pressure of the ear tended to increase in rabbits immediately after immobilization (15.8 +/- 3.1 mm Hg) compared with control rabbits (8.5 +/- 2.3 mm Hg), and the difference became significant when volume load was exerted on both groups of rabbits (20.8 +/- 7.4 versus 9.2 +/- 4.8 mm Hg, p = 0.0211). In conclusion, we clearly demonstrated that physical stress due to immobilization, especially in combination with volume load, increased intraocular pressure in rabbits.