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John G. Flanagan, Aphrodite Dracopoulos, Inka Tertinegg; Continuous Scleral Intraocular Pressure Monitoring in a Live Porcine Model. Invest. Ophthalmol. Vis. Sci. 2012;53(14):2496.
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To assess the feasibility of continuous intraocular pressure (IOP) monitoring from the sclera in a live porcine model.
Six Yorkshire strain pigs, 30-50kg were used. The animals were anesthetized with isoflurane administered with 100% oxygen delivered through a facemask. Eyes were anesthetized with 0.5% proparacaine hydrochloride. A strain gauge sensor (Omega Engineering, Inc., Stamford, CT) was mounted with 100% cyanoacrylate to the conjunctiva approximately 1-2 mm from the limbal margin in the superior temporal region of the pig’s eye. The animals were anesthetized with isoflurane administered with 100% oxygen delivered through a facemask. Eyes were anesthetized with 0.5% proparacaine hydrochloride. The anterior chamber was cannulated using a 27-gauge needle introduced from the temporal limbus and connected to a 30ml syringe filed with normal saline on a stand with variable height. Another 27-gauge needle was inserted into the anterior chamber through the nasal limbus primed with degassed water and connected to a pressure transducer. Adjusting the height of the syringe generated IOP changes and was recorded with a commercial software program (TracerDAQ™ Software, MicroDAQ.com Ltd., Contoocook, NH). IOP was increased in increments of 7mmHg from 0 to 44 mmHg (± 1.0 mmHg) and the surface deformation of the strain gauge sensor was recorded for each incremental step. IOP changes were repeated three times to establish reproducibility and linearity of the strain gauge sensor.
IOP measurements and surface deformation of the strain gauge sensor responded linearly with changes in ocular pressure in a live pig model (n=6). Analysis of variance gave a significant difference for strain gauge deformation with IOP manipulations (p<0.005). There was also good correlation between the 2 varibles with rho values ranging from 0.830 to 0.949 with increasing IOP and 0.808 and 0.975 with decreasing IOP.
These proof-of-principle experiments are an essential step to the realization of a scleral mounted, 24-hour IOP recording device. Changes in IOP can be accurately assessed by measuring changes in the radius of curvature of the sclera in a live porcine model.
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