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Simon Bello, Sharad Malavade, Christopher L Passaglia; Development of an implantable system for controlling intraocular pressure in rats. Invest. Ophthalmol. Vis. Sci. 2014;55(13):2168.
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To devise a system for continuously recording and regulating intraocular pressure in a rat’s eye in order to induce ocular hypertension and monitor IOP fluctuations on a 24-hour basis.
The system consists of a pressure sensor, a controller, and a fluid micropump; these elements interact with the rat’s eye via a special cannula implanted in the anterior chamber. The tubing, filled with artificial aqueous humor, is tunneled subcutaneously from an incision in the scalp to the orbit of the eye. A novel surgical procedure was developed to penetrate the cornea and hold the cannula in place without damaging internal ocular structures, even though the eye moves. The cannula directly conducts pressure from inside the eye to the pressure sensor. IOP signals were then sent to a data acquisition board for analysis and display. The system was tested by exposing it to constant hydrostatic pressure for weeks on end. It was also used on rats under ketamine anesthesia to record natural IOP fluctuations for 12-48 hours and to hold IOP at set levels of 10-50mmHg for several hours each.
The system successfully recorded long term data with a resolution of 0.2mmHg, noise oscillations of less than 1mmHg, and no drift under constant hydrostatic pressure. When the system was connected to anesthetized rats, circadian rhythms in IOP with fluctuations of up to 10mmHg were recorded. When the system set point was changed, IOP was raised or lowered to the specified pressure level in a few seconds and then maintained within ±3 mmHg of that level. Little-to-no sign of physical or physiological damage was evident to the rat’s eye after months of cannula implantation.
Results show that cannulation of the anterior chamber of a rat’s eye is possible and its combination with a dynamic feedback system allows researchers to continuously record and regulate IOP for long periods of time, paving the way towards an implantable IOP control system for rats and larger animals.
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