Corneal Resistance Factor Calculation for IOP-Independent Biomechanical Assessment
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Solution Overview
Problem
Current non-contact tonometers provide incomplete characterization of corneal biomechanical state, as corneal hysteresis is not independent of intraocular pressure and shows poor correlation with central corneal thickness, limiting their ability to assess corneal properties accurately.
Innovation Solution
A method and apparatus to measure corneal resistance to deformation by calculating a corneal resistance factor (CRF) using empirically derived functions from pressure values obtained during non-contact tonometry, minimizing dependence on intraocular pressure and maximizing correlation with central corneal thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If corneal hysteresis is used to characterize corneal biomechanical state, then measurement can be obtained from non-contact tonometry, but the measurement is not independent of intraocular pressure and shows poor correlation with central corneal thickness
Solution Approach 1:
The patent transforms the single parameter (corneal hysteresis) into multiple parameters (P1, P2, and their ratio P1/P2) to comprehensively characterize corneal biomechanical properties. By using the ratio P1/P2 instead of the difference P1-P2, the measurement becomes independent of intraocular pressure while maintaining correlation with central corneal thickness, thus resolving the contradiction between measurement precision and reliability
Solution Approach 2:
The patent creates a composite measurement approach by combining multiple pressure parameters (P1 and P2) into a unified corneal resistance factor (CRF) calculation. This composite parameter integrates both applanation pressures to provide a more complete characterization of corneal properties that is independent of IOP and correlates better with central corneal thickness
2Productivity
If conventional non-contact tonometry is used to measure intraocular pressure, then IOP values can be obtained, but corneal effects significantly impact the readings reducing measurement reliability
Solution Approach 1:
The patent extracts the corneal resistance factor (CRF) as a separate measurement from the conventional IOP measurement process. By calculating CRF = P1/P2 independently from the standard IOP calculation, the system separates corneal property assessment from IOP measurement, allowing each to be optimized independently and improving overall measurement precision without sacrificing productivity
3Device complexity
If a single applanation pressure is used to calculate IOP, then the measurement process is simple, but incomplete corneal biomechanical information is obtained
Solution Approach 1:
The patent segments the corneal deformation process into two distinct phases: inward applanation (P1) and outward applanation (P2). By analyzing both phases separately and calculating their ratio, the system obtains complete corneal biomechanical information while maintaining relatively simple calculation procedures, thus resolving the contradiction between simplicity and information completeness
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
The corneal resistance factor effectively indicates corneal resistance, providing a more complete characterization of corneal properties, improving accuracy in assessing keratoconus and changes post-surgical alterations, and demonstrating significant correlation with central corneal thickness.
Implementation Method 1
directing a fluid pulse at a cornea to cause reversible deformation of the cornea from an original state of convexity through a first state of applanation to a state of concavity
Implementation Method 2
an optoelectronic system monitors the cornea by detecting corneally reflected light from a beam obliquely incident upon the cornea
Implementation Method 3
a pressure transducer measures the pump plenum pressure as the pulse is generated to provide a plenum pressure signal
Data Source
AI summary
A method and apparatus for measuring corneal resistance to deformation use an empirically derived function wherein an inward applanation pressure P1 and an outward applanation pressure P2 obtained during a corneal deformation cycle caused by a fluid pulse are separately weighted so as to minimize dependence of the calculated corneal resistance factor (CRF) on intraocular pressure. In one embodiment, the function is optimized, at least in part, to maximize statistical correlation between the calculated corneal resistance factor (CRF) and central corneal thickness.