Intraocular Pressure Measurement with Pneumatonometry and a Tonometer Tip Cover During Negative Pressure Application

Purpose: This is a 2-part study to investigate the agreement between pneumatonometry and direct pressure transducer intraocular pressure ( IOP) measurements in a perfusion organ culture (POC) model where (1) the perfusion fluid column is open to atmospheric pressure, holding IOP constant to permit evaluation of the impact of negative pressure (NP) on IOP measurements, and (2) the perfusion fluid column is a closed system, allowing IOP to vary with NP application. Methods: The first part incorporated a fluid column open to atmospheric pressure, maintaining IOP constant to permit evaluation of the effect of applied NP on IOP measurement accuracy. In the second part, the POC column was closed, allowing IOP to vary with NP application and permit evaluation of agreement between pneumatonometry and pressure transducer measurements. In each part, four perfused tissues were used in thirteen paired pre-set IOP (10, 20, 25, 30 mmHg) and NP (0, 5, 10, 15, 20 mmHg) combinations, resulting in a total of 1040 paired measurements (520 per study). The difference in IOP measurements (Delta IOP = Excursion tonometry - pressure transducer) was calculated at each paired configuration. Results: During the first part, the mean Delta IOP was -0.7 +/- 1.6 mmHg across all measurements. During the second part, the mean Delta IOP across all measurements was +0.7 +/- 1.4 mmHg. At NP settings of -5, -10, -15, and -20 mmHg, across all pre-set IOPs, the mean TOP reduction via Excursion tonometry was 3.1 +/- 0.3, 5.6 +/- 1.3, 8.5 +/- 1.7 and 11.2 +/- 1.8 mmHg, respectively. Conclusion: Measurement of IOP via Excursion tonometry yields results within the accuracy range of the pneumatonometry device (per manufacturer) and is minimally impacted by NP application. The IOP-lowering results are consistent with previous studies and further support the effectiveness of the Multi-Pressure Dial in lowering IOP relative to atmospheric pressure.