Does Rebound Tonometry Probe Misalignment Modify Intraocular Pressure Measurements in Human Eyes?

Abstract

Purpose. To examine the influence of positional misalignments on intraocular pressure (IOP) measurement with a rebound tonometer. Methods. Using the iCare rebound tonometer, IOP readings were taken from the right eye of 36 healthy subjects at the central corneal apex (CC) and compared to IOP measures using the Goldmann applanation tonometer (GAT). Using a bespoke rig, iCare IOP readings were also taken 2 mm laterally from CC, both nasally and temporally, along with angular deviations of 5 and 10 degrees, both nasally and temporally to the visual axis. Results. Mean IOP ± SD, as measured by GAT, was 14.7 ± 2.5 mmHg versus iCare tonometer readings of 17.4 ± 3.6 mmHg at CC, representing an iCare IOP overestimation of 2.7 ± 2.8 mmHg (P < 0.001), which increased at higher average IOPs. IOP at CC using the iCare tonometer was not significantly different to values at lateral displacements. IOP was marginally underestimated with angular deviation of the probe but only reaching significance at 10 degrees nasally. Conclusions. As shown previously, the iCare tonometer overestimates IOP compared to GAT. However, IOP measurement in normal, healthy subjects using the iCare rebound tonometer appears insensitive to misalignments. An IOP underestimation of <1 mmHg with the probe deviated 10 degrees nasally reached statistical but not clinical significance levels.

Monitoring daily intraocular pressure fluctuations with self‐tonometry in healthy subjects

“…Beasley et al. () found that angular deviations of 5° and 10° had no statistical significance, except for 10° nasally and concluded, however, that this should not have any clinical significance. To obtain the most accurate measurements, perhaps users should be allowed additional training time to achieve optimal alignment at the centre of the cornea.…”

Evaluation of intraocular pressure estimates obtained using an iCare rebound tonometer

“…On the other hand, the small probe used by an inexperienced user can give errors from off‐centre placement and misalignment of the instrument and probe on the cornea. Investigators have evaluated the influence of probe placement at various locations of the cornea, including errors due to various angling of the probe . Prior studies have not evaluated differences in measurement as a function of a small displacement of 1.5 mm from the centre, which is quite possible under real clinical circumstances.…”

Self‐tonometry as a complement in the investigation of glaucoma patients

“…Attempts have been made in the past to develop home tonometers (Asrani et al 2000, Marchini et al 2002, Meyer et al 2006. Rebound tonometry as developed by iCare Ò has been used by healthcare professionals since 2003, and clinical studies have demonstrated high agreement between GAT and iCare Ò results (Brusini et al 2006, Davies et al 2006, Nakamura et al 2006, J ohannesson et al 2008, Burr et al 2012, Beasley et al 2013, Moreno-Montanes et al 2015. In iCare Ò devices, which do not require the use of anaesthesia, a lightweight probe rebounds from the cornea.…”