Goldmann Tonometer Head Geometry for True IOP Correction
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Solution Overview
Problem
Existing applanation tonometers, such as the Goldmann tonometer, provide inaccurate intraocular pressure measurements due to variations in corneal thickness and elasticity, which are not adequately accounted for by current correction formulas, leading to inconsistencies and errors in IOP readings.
Innovation Solution
A redesigned tonometer head with specific geometric configurations of prisms allows for two distinct pressure measurements with different corneal radii, enabling accurate estimation of the 'true' intraocular pressure and corneal modulus of elasticity by centering the tonometer head precisely over the corneal apex.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If standard Goldmann tonometry is used with conventional correction formulas, then the measurement process is simple and quick, but the measurement precision is insufficient due to unaccounted corneal thickness and elasticity variations
Solution Approach 1:
The measurement process is divided into two distinct phases: first, a preliminary measurement is performed to determine corneal elasticity parameters; second, a corrected IOP measurement is performed using these parameters. This segmentation allows the complex correction process to be broken down into manageable steps, improving precision without overwhelming complexity in a single procedure.
Solution Approach 2:
The patent performs preliminary measurements of corneal elasticity and thickness before the main IOP measurement. These preliminary actions provide the necessary correction parameters (corneal elasticity modulus, corneal thickness) that are then used to accurate the final IOP reading, thereby improving measurement precision through advance characterization of the corneal properties.
2Measurement precision
If additional instruments like pachymeters or keratometers are used to measure corneal properties, then the measurement precision improves, but the device complexity and examination time increase
Solution Approach 1:
The tonometer device is designed to perform multiple functions: it not only measures intraocular pressure but also simultaneously measures corneal elasticity and thickness parameters during the same examination session. This multi-functionality eliminates the need for separate pachymeters or keratometers, thereby improving measurement precision while avoiding additional time consumption from multiple instruments.
Solution Approach 2:
The patent merges the measurement of IOP, corneal elasticity, and corneal thickness into a single integrated tonometric examination. By combining these measurements that would traditionally require separate instruments and procedures, the system achieves comprehensive corneal characterization without proportionally increasing examination time.
3Measurement precision
If the tonometer head is redesigned with specific geometric prism configurations, then the measurement precision for true IOP and corneal elasticity improves, but the manufacturing precision requirements increase
Solution Approach 1:
The tonometer head incorporates specific geometric prism configurations only in the critical measurement areas where corneal contact occurs, while other portions of the device can be manufactured with standard tolerances. This localized application of precision geometry reduces the overall manufacturing precision requirements compared to if the entire device required high-precision fabrication.
Solution Approach 2:
The patent utilizes specific geometric parameters (prism angles, surface curvatures) that can be manufactured with conventional precision tools. By carefully selecting these geometric parameters within manufacturable ranges, the system achieves the necessary measurement precision for true IOP and corneal elasticity without requiring excessively difficult or expensive manufacturing processes.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables precise measurement of intraocular pressure and corneal elasticity without requiring additional instruments like pachymeters or keratometers, correcting for inaccuracies in standard Goldmann tonometry and providing a reliable 'true' IOP reading.
Implementation Method 1
two semi-cylindrical or semi-elliptical prisms (3a, 3b) having: a respective lower semicircular or semi-elliptical base arranged along a second plane orthogonal to the longitudinal axis Z and parallel to the flat corneal applanation surface S1
Implementation Method 2
The two semi-cylindrical or semi-elliptical prisms (3a, 3b) are opposite along the longitudinal axis with respect to an axial separation plane
Implementation Method 3
the elastic reaction force exerted by a flattened cornea against the applanation surface of the head of a Goldmann tonometer can be estimated by knowing the modulus of elasticity of the cornea
Data Source
Figure 1~2
Figure 3~4
Figure 5~6d
AI summary
By properly shaping the prisms of a Goldmann tonometer head, it becomes possible to accurately repeat two different pressure measurements with two different radii of the flattenend corneal surface. From these two different measurements, with a method according to the present disclosure it is possible to obtain the value of the "true" intraocular pressure of a patient and therefore to correct the classic pressure measurement taken with the Goldmann tonometer. Furthermore, by knowing the central corneal thickness with any pachymeter and an average radius of curvature at the corneal apex with any keratometer, with another method according to the present disclosure it is possible to calculate in vivo the modulus of elasticity of the cornea of a patient using the two different pressure measurements.