Measurement of intraocular pressure by telemetry in conscious, unrestrained rabbits

The aim of this study was to develop a system for the continuous recording of the intraocular pressure (IOP) in rabbits maintained in their normal environment. A telemetric system originally designed for the measurement of cardiovascular parameters in unrestrained, conscious laboratory animals was adapted for this purpose.

Experiments were performed in adult albino female rabbits. The transmitter was placed under the skin in the neck region. Its catheter was tunneled subcutaneously to the superior conjunctival sac and inserted into the midvitreous. Correlation with the IOP in the anterior chamber was performed by pneumatonography measurement and by manometric pressure perfusion in the implanted rabbits. Transitory increase in IOP was induced by a rapid intravenous injection of 20 ml/kg of 5% glucose. Timolol maleate (0.5%) or saline was administered (50 microliters) in the instrumented eye before the intravenous glucose injection.

The intraocular catheter remained patent and was well tolerated for at least 2 months. A constant circadian rhythm of IOP was recorded as previously reported. Intraocular pressure measurements were highly correlated to pneumatonographic and to manometric measurements, indicating the accuracy and reliability of the recording system. A significant inhibition of the IOP increases following the intravenous injection of glucose was induced by 0.5% timolol treatment when compared to saline instillation.

The continuous recording of IOP by our telemetric method represents a breakthrough for studying the effect of various pharmacologic agents in conscious, unrestrained rabbits under physiological conditions that have not been possible with previously described methods.