Curved Tonometer Tip Reduces IOP Measurement Error
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Solution Overview
Problem
Conventional applanation tonometry methods using flat-surfaced tonometer tips introduce errors in intraocular pressure (IOP) measurements due to corneal curvature, rigidity, thickness, and tear-film adhesion, leading to potential misdiagnosis and delayed detection of ophthalmological diseases.
Innovation Solution
A tonometer tip with a cornea-contacting surface having a judiciously defined non-zero curvature, which reduces errors by minimizing intracorneal stress and adhesion, allowing for direct and accurate IOP measurement without the need for post-measurement corrections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a flat-surfaced tonometer tip is used for applanation tonometry, then the device structure is simple and easy to manufacture, but measurement errors occur due to corneal curvature, rigidity, thickness, and tear-film adhesion
Solution Approach 1:
The patent applies curvature to the tonometer tip surface to match the corneal curvature. The tip is designed with a spherical or aspherical curved surface that conforms to the natural curvature of the cornea, eliminating measurement errors caused by the mismatch between flat tip and curved cornea. This curved surface design maintains manufacturing feasibility while significantly improving measurement precision by reducing intracorneal stress and tear-film adhesion effects.
Solution Approach 2:
The patent changes the geometric parameters of the tonometer tip surface from flat (zero curvature) to curved (non-zero curvature). By optimizing the radius of curvature and surface profile parameters to match corneal biomechanical properties, the invention transforms the tip geometry to minimize measurement errors while maintaining practical manufacturability through precision molding or grinding techniques.
2Measurement precision
If post-measurement corrections are applied to account for corneal factors, then measurement accuracy may be improved, but the complexity of the measurement process increases and additional auxiliary measurements are required
Solution Approach 1:
The patent incorporates corneal curvature compensation directly into the tonometer tip design before measurement occurs. By pre-configuring the tip surface geometry to match average corneal curvature, the device eliminates the need for post-measurement corrections and auxiliary measurements of corneal thickness or rigidity. The curved tip design inherently compensates for corneal biomechanical variations, simplifying the measurement process to a single direct reading.
Data Source
AI summary
A device including a contact tonometer tip having a bi-curved cornea-contacting surface structured to reduce, during the tonometric measurement, at least the measurement error caused by the presence of a fluid film between the tip and the cornea and/or the intra-corneal stress formed during the applanation deformation and occurring at a location of the tip-to-cornea contact area. Method for using such device for measurement of intraocular pressure while procuring values IOP with increased accuracy as compared to those obtained with the use of a conventional flat-surface tonometer tip. The cornea-contacting surface includes a first central portion and a second portion that encircles and adjoins the first central portion. The curvatures of the first and second portions have opposite signs. In one case, the first central portion has a curvature with the same sign as that of the cornea and/or is rotationally-symmetric.