Acute systemic hemodynamic effects on intraocular pressure in rats with unilateral experimental ocular hypertension

Abstract

 

Purpose

 

To evaluate the effects of acute systemic arterial blood pressure (ABP) and central venous pressure (CVP) surges on intraocular pressure (IOP) in ocular hypertensive and normal eyes of rats.

 

Methods

 

Unilateral ocular hypertension (OHT) was established in Sprague-Dawley rats by serial weekly intracameral injection of microbeads. Continuous IOP waveform recordings from the anterior chamber were performed using solid-state 1.2F micro-sensors under urethane anesthesia. The effects on IOP during hemodynamic challenges using phenylephrine (PE) (50μg/kg/min i.v.) or rapid isotonic saline loading (20ml/kg over 1 min i.v.) were studied in both eyes.

 

Results

 

Over a 10-week period, IOP significantly increased by 53% (P < 0.05) in the unilateral microbead-induced OHT eyes. Both ABP and the IOP were significantly elevated during PE infusion compared to baseline (P < 0.05, Figure 1). A significantly greater IOP increase was found in the experimental OHT eyes compared to contralateral control eyes with maximal increases of 1.46 ± 0.2 mmHg and 0.94 ± 0.1 mmHg respectively (P < 0.05). Correspondingly, the OHT eyes had a significantly higher baseline IOP pulse amplitude and also a greater increase in pulse amplitude during PE infusion compared to control eyes (P < 0.0001). A rapid and sustained rise in IOP secondary to saline loading was observed in both OHT eyes and control eyes with a significantly greater rise observed among OHT eyes (P < 0.0001).

 

Conclusions

 

Intravenous administration of PE results in a temporary ABP rise and a transient intraocular hypertensive response. In contrast, surges in CVP results in a more sustained rise in IOP. The response was more pronounced in eyes with experimental glaucoma compared to normal eyes which emphasizes the importance of an intact outflow facility for dampening fluctuations in IOP. The fluid challenge mimics the effects seen in a water drinking test with a greater rise and prolonged recovery time.

 

 

Figure 1. IOP and mean arterial pressure (MAP) during and following IV phenylephrine infusion (50μg/kg/min). Start and finish of the infusion over 2 minutes indicated by arrows. IOP rise in OHT eyes was significantly greater than control eyes (values are mean ± SEM, n=7, *P < 0.05).

 

Keywords: 637 pathology: experimental • 568 intraocular pressure