Corneal Astigmatism Fitting via Toric Aspheric Model
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Solution Overview
Problem
Current methods for determining astigmatism parameters from corneal height data suffer from poor repeatability, which can lead to inaccurate results, especially in the measurement of the astigmatism angle, where small errors can render astigmatic corrections useless.
Innovation Solution
A method involving the use of a stimulator source with multiple point light sources to create a height map of the cornea, followed by surface fitting using global functions like Zernike polynomials, and subsequent fitting to a toric aspheric model for accurate and repeatable determination of astigmatism parameters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If 1-dimensional fits are made along various meridians to determine astigmatism parameters, then the measurement process is simple, but the repeatability is poor
Solution Approach 1:
The patent transitions from 1-dimensional meridian fitting to 2-dimensional surface fitting using a toric aspheric model. This dimensional upgrade allows the method to analyze the entire corneal surface simultaneously, improving repeatability by reducing the impact of localized measurement errors while maintaining operational feasibility through automated computational processing.
2Device complexity
If 1-dimensional fits are used to determine astigmatism parameters, then the calculation is computationally simple, but the accuracy is insufficient
Solution Approach 1:
The patent employs a 2-dimensional toric aspheric model that fits the entire corneal surface rather than individual meridians. This approach increases computational complexity but significantly improves accuracy by utilizing all available height data points simultaneously and reducing the influence of measurement errors through global optimization.
Solution Approach 2:
The patent combines multiple measurement data points from the entire corneal surface into a unified 2-dimensional fitting process. By merging all height data into a single comprehensive model, the method achieves higher accuracy while the automated computational approach manages the increased complexity efficiently.
3Stability of the object's composition
If global functions are used for surface fitting, then the overall surface representation is improved, but local variations may be smoothed out
Solution Approach 1:
The patent applies local quality by using a toric aspheric model that can represent different curvatures in different regions of the cornea. The model incorporates local astigmatism characteristics through its mathematical formulation, allowing accurate representation of both global surface shape and local variations in corneal curvature.
Solution Approach 2:
The patent employs a toric aspheric model that captures the curved, non-spherical nature of the corneal surface. This model uses curvature parameters to represent both the overall spherical shape and local aspheric variations, maintaining stability in global representation while preserving local detail through its mathematical structure.
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
This approach improves the repeatability and accuracy of astigmatism parameter determination without compromising precision, using point-to-point information and 2-dimensional fitting to the toric aspheric model, reducing the impact of measurement errors.
Implementation Method 1
capturing a reflected image of the plurality of point sources and determining a position of reflections of the respective plurality of point sources from the captured reflected image
Data Source
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Figure 4(a)~4(b)
AI summary
A method of determining global shape parameters of a cornea is disclosed, the method comprising: -determining a height map of a cornea by: i. Illuminating a cornea of an eye using a stimulator source comprising a plurality of point sources; ii. capturing a reflected image of the plurality of point sources and determining a position of reflections of the respective plurality of point sources and iii. deriving the height map of the cornea based on a position of the plurality of point sources and the position of the reflections of the respective plurality of point sources; - fitting the height map as derived to a toric aspheric model to obtain a global fitting of the corneal surface to the toric aspheric model and; - using the global fitting to determine one or more parameters related to an astigmatism of the cornea.