Error in measurement of intraocular pressure with the Icare and IcarePRO

Purpose: We sought to determine whether changes in the measurement angle of the Icare TA01i and IcarePRO tonometers led to errors in the measurement of intraocular pressure (IOP). Methods: In this prospective, single-facility study, we analyzed 77 patients from November 2017 to September 2019. We measured IOP with the Icare TA01i and IcarePRO while changing the angle of the device with the cornea center and analyzed the associated changes in the measurement. Results: IOP measured with the Icare tilted − 30°, − 15° vertically was significantly higher than that measured with the Icare tilted horizontally (p < 0.0001, p < 0.0001). The IOP measured with a + 10° vertical tilt was significantly lower than that measured horizontally (p < 0.0001). When the IcarePRO was tilted + 90° vertically, the IOP was significantly lower with the patient in the supine position than in the lateral position (p = 0.00058). Conclusions: IOP measured with the Icare and IcarePRO is affected by the measurement angle. The study results will direct the clinicians to exercise extra precautions in determining the measurement angle while measuring IOP.