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D. C. Lozano, N. Rodriguez, N. Patel, M. D. Twa; Accuracy and Reproducibility of Intraocular Pressure Measurements in the Brown Norway Rat Using the TonoLab Rebound Tonometer. Invest. Ophthalmol. Vis. Sci. 2009;50(13):2853.
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To evaluate the accuracy and reproducibility of the TonoLab rebound tonometer in the Brown Norway rat and to determine a standard calibration curve for the use of this tonometer in this species.
One eye from each of five male Brown Norway rats (average weight = 288 g) was cannulated with a 30 gauge needle that was connected in-line to a calibrated pressure transducer.One examiner raised or lowered intraocular pressures in predetermined randomized steps of 5 or 10 mm Hg (range 5 to 65 mm Hg) by adjusting a fluid-filled syringe, while another masked examiner measured intraocular pressure with the TonoLab. Each IOP measurement was the product of six individual applanations. These measurements were repeated ten times at each pressure level (n = 13 levels). Linear and non-linear regression analyses were performed to determine the best calibration functions for the TonoLab tonometer. The 95% limits of agreement were calculated using Bland-Altman analysis.
The preferred calibration curve over the full range of IOP tested was sigmoidal (P<0.0001, R2 =0.98). The TonoLab consistently overestimated pressures lower than 10 mmHg, while it underestimated pressures greater than or equal to 55 mm Hg. The best-fitting calibration function for IOP between 15-50 mm Hg was linear (y = 0.97x - 2.238, r2 = 0.98). Over this range, the average 95% prediction interval was ± 3.55 mm Hg. The 95% limits of agreement between TonoLab and transducer over the 15-50 mm Hg range were ± 3.31 mm Hg.
The TonoLab rebound tonometer is a repeatable and accurate method of measuring intraocular pressure in the Brown Norway rat. Non-linear regression analysis demonstrated that the relationship between TonoLab and the pressure transducer is best described by a sigmoidal curve and that measurement performance was linear from 15-50 mm Hg.
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