Trans-scleral tactile tonometry: an instrumented approach

Area of Science:

• Ophthalmology and Biomedical Engineering
• Ocular Biomechanics

Background:

• Accurate intraocular pressure (IOP) measurement is crucial for diagnosing and managing glaucoma.
• Current tonometry methods have limitations, necessitating novel approaches for improved accuracy and ease of use.
• Digital palpation tonometry offers a principle for IOP assessment, but requires precise instrumentation.

Purpose of the Study:

• To investigate the feasibility of a novel trans-scleral tonometer utilizing instrumented digital palpation.
• To validate the tonometer's performance using enucleated porcine eyes and an analytical model.
• To determine optimal conditions for accurate IOP measurement with the novel device.

Main Methods:

• Development and testing of a trans-scleral tonometer with two offset force probes.
• Experimental validation using enucleated porcine eyes, including distention and indentation tests.
• Analysis of force-indentation data using an analytical model accounting for aqueous humor outflow and visco-elastic properties.

Main Results:

• Observed force data hysteresis attributed to stress relaxation in the corneo-scleral shell.
• Identified optimal indentation rates below 0.5 mm/s for accurate IOP measurement (10-35 mmHg).
• Established a calibration curve: 10 mN force variation correlates to 1 mmHg IOP change.

Conclusions:

• The novel trans-scleral tonometer demonstrates feasibility for IOP measurement.
• Accurate IOP readings require controlled indentation rates and appropriate pressurization methods (anterior chamber preferred).
• The device shows promise for clinical application, potentially with a contoured facial mask implementation.