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A. Doelemeyer, E.A. Polska, L. Schmetterer, G.N. Lambrou; Evaluation of Telemetric Measurements of Intraocular Pressure Using Acute Hydrostatic IOP Elevation in Non–Human Primates . Invest. Ophthalmol. Vis. Sci. 2005;46(13):1258.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To validate IOP measurements performed with an implanted radio–telemetric pressure sensor at different levels of IOP increased step–wise by hydrostatic pressure. Telemetric and tonometric measurements were taken simultaneously and compared. Methods: In 4 cynomolgous monkeys radio–telemetry based pressure sensors (Data Science International) were introduced unilaterally into the vitreous and the battery/sender units were placed subcutaneously on top of the sculls. Prior to this procedure ocular hypertension was induced in these eyes by photocoagulation of the trabeculum. On the day of experiments a needle was introduced into the vitreous entering through the pars plana and connected to a physiological saline reservoir to force hydrostatic pressure levels. Pressure was increased step–wise, first to an initial baseline value corresponding to 20 – 30 cm height difference between reservoir and the eye and then by steps of 10 cm up to an equivalent IOP of 70 to 90 mmHg. IOP was increased in this fashion every 4 to 5 minutes and measured using Tonopen [ XL (Mentor)] after 2 minutes in each interval. During experiments animals were anesthetized. At the end of experiment animals were euthanized. The decision to euthanize the animals was taken for reasons independent of the aims of the present study. The ARVO guidelines for the Use of Animals in Ophthalmic and Visual Research were followed. Results: Height–adjustment of the physiological saline reservoir forces a well defined elevation of IOP that can be calculated from the height difference based on physical laws (Δh 10 cm ≈ Δp 7.36 mmHg). The telemetric IOP measurements were well in accordance with the theoretical values for all 4 monkeys (relative error 60 mmHg). The telemetric IOP measurements at a given pressure showed a small pulse amplitude (approx. 0.5 mmHg peak–to–peak at physiological levels). This amplitude increased with increasing IOP. Conclusions: Changes in IOP can be measured accurately with an implanted telemetry–based pressure sensor. In addition, the telemetric system allows continuous IOP recording for long time periods. The implant makes the use of anesthetics for measurements in non–human primates redundant, avoiding negative influence on IOP results. The use of the Tonopen may be limited, especially when measuring high intraocular pressures.
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