Does rebound tonometry probe misalignment modify intraocular pressure measurements in human eyes?

Area of Science:

• Ophthalmology
• Biomedical Engineering
• Medical Devices

Background:

• Intraocular pressure (IOP) is a key metric in diagnosing and managing glaucoma.
• Rebound tonometry offers a portable and non-invasive method for IOP measurement.
• Understanding the accuracy and limitations of rebound tonometers, such as the iCare device, is crucial for clinical application.

Purpose of the Study:

• To evaluate the impact of positional misalignments on IOP measurements obtained with the iCare rebound tonometer.
• To compare iCare tonometer readings against Goldmann applanation tonometer (GAT) measurements under various conditions.

Main Methods:

• IOP was measured in 36 healthy subjects using the iCare rebound tonometer at the central corneal apex (CC) and compared with GAT.
• The iCare tonometer was also used to take readings at lateral displacements (2 mm nasal/temporal) and angular deviations (5° and 10° nasal/temporal) from the visual axis.
• A bespoke rig was utilized to control positional accuracy during measurements.

Main Results:

• The iCare tonometer consistently overestimated IOP compared to GAT (17.4 ± 3.6 mmHg vs. 14.7 ± 2.5 mmHg, P < 0.001).
• This overestimation increased with higher average IOPs.
• IOP measurements were not significantly affected by lateral displacements.
• Marginal underestimation of IOP was observed with angular deviations, reaching statistical significance only at 10° nasally (<1 mmHg).

Conclusions:

• The iCare rebound tonometer overestimates IOP relative to GAT, a known limitation.
• Despite this, the iCare tonometer demonstrates robustness against positional misalignments in healthy individuals.
• Minor angular deviations, such as 10° nasally, result in statistically, but not clinically, significant underestimations.