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Christopher Passaglia, Simon Bello, Radouil Tzekov, Sharad Malavade; Development of an implantable system for measuring intraocular pressure in rats. Invest. Ophthalmol. Vis. Sci. 2013;54(15):5657.
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To devise a method of continuously recording the intraocular pressure of a rat's eye in order to monitor pressure changes induced by experimental glaucoma or other processes on a 24-hr basis.
The system consists of a small custom-designed pressure sensor connected directly to the anterior chamber of the eye via a cannula and fine-bore tubing. The pressure sensor was fabricated by removing the plunger of a 1ml syringe, cutting the syringe down in length, and gluing over the cut end a thin plastic film which acts as a diaphragm. A small semiconductor strain gauge was then glued to the outside surface of the diaphragm and sealed. The leads of the strain gauge were connected to an electronic circuit consisting of a small battery, a Wheatstone bridge, an amplifier, and a filter. The pressure signal sensed by the circuit will ultimately be transmitted wirelessly to a receiver, but for testing purposes was sent to a data acquisition board for analysis and display. The syringe and connective tubing were filled with artificial aqueous humor, and the tubing was tunneled subcutaneously from an incision in the scalp to the eye orbit and out a small hole in the conjunctiva near the limbus. Due to the small dimensions of the rat eye, a special cannula and surgical procedure was developed to penetrate the cornea and maintain the cannula in place without damaging the iris or other internal structures.
The system was tested by applying hydrostatic and hydrodynamic pressure directly to the sensor at first and then indirectly via a second cannula in the rat eye. Pressure amplitude was varied by randomly altering the height of a saline bath connected to a manometer in parallel with the sensor. The height variations caused an injection or aspiration of fluid through the cannula, which deflected the sensor diaphragm and generated a stable pressure voltage signal that was detectable up to 80 mmHg with a resolution of <0.5mmHg.
The results show that it is possible to cannulate the anterior chamber of the rat eye and directly record intraocular pressure for a prolonged period of time with a pressure sensor that is implantable in a rat, which paves the way for chronic studies in awake animals.
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