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Sean Joesph McCafferty; Goldmann applanation tonometer error relative to true intracameral Intraocular pressure in vitro and in vivo. Invest. Ophthalmol. Vis. Sci. 2017;58(8):1597.
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© ARVO (1962-2015); The Authors (2016-present)
Examine Goldmann applanation tonometer bias to intracameral intraocular pressure (IOP) in both human cadaver eyes and live human eyes. Also examine IOP bias changes due to patient position, and corneal biomechanical properties.
Twenty one (21) fresh human cadaver globes were manometrically modulated between 5 and 60 mmHg IOP measured by intracameral pressure transducer. IOP was measured with a Goldmann Applanation Tonometer (GAT) in both upright and supine positions. Central corneal thickness (CCT) was measured as an indication of corneal hydration. Additionally, eight (8) patients undergoing cataract surgery were manometrically adjusted to 20 mmHg IOP measured by intracameral pressure transducer. Prior to surgery, corneal resistence factor (CRF) was measured with an Ocular Response Analyzer (ORA) and CCT was measured. IOP was measured with a Perkins applanation tonometer in both supine and upright positions.
The GAT tonometer measured IOP in cadaver eyes was 3.06+/-2.4 mmHg lower than intracameral transducer IOP in the upright postion and 5.09+/- 2.6 mmHg in the supine position (p<.05). The Goldmann IOP measurement varied with corneal hydration as measured by CCT (747+/-66 microns) by 4.2 mmHg (correlation coeff.=0.23). The GAT IOP measured on live human eyes was 2.75 +/-2.10 mmHg lower than intracameral transducer IOP in the upright postion and 4.81+/- 2.87 mmHg lower in the supine postion. CCT in the surgical eyes (546+/- 32 microns) indicated an IOP error correlation of 3.9 mmHg lower in thin corneas compared to thick corneas within the sample range (correlation coeff.=0.28). Likewise, CRF (9.1+/-2.1) trended toward a lower GAT measured IOP in corneas with a low CRF as compared to a high CRF by 4.0 mmHg within the sample range (correlation coeff=0.18)
Goldmann IOP measures significantly lower than true intracameral IOP by about 3 mmHg in fresh cadaver eyes and this bias is confirmed in live human eyes. Supine position increases the IOP measurement bias to about 5 mmHg. Central corneal thickness (CCT) and corneal resistence factor (CRF) both appear to significantly affect the IOP measurement error by up to an additional 4 mmHg correlated over the ranges tested. These findings are useful in understanding the biomechanical effects creating both overall Goldmann IOP measurement bias and errors due to corneal biomechanical variability seen in patients.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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