Customized IOL Power Calculation Using Ray Tracing and MTF
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Solution Overview
Problem
Current regression-based methods for calculating intraocular lens (IOL) power, such as the SRK, SRK II, and SRK/T formulas, fail to provide accurate predictions for eyes that have undergone ablative forms of keratorefractive surgery, like LASIK, due to their reliance on historical clinical data and neglect of optical aberrations, leading to suboptimal IOL power selection for patients with non-normal eye dimensions or aberrations.
Innovation Solution
A system and method that measures anterior and posterior corneal topography, axial length, and anterior chamber depth, and uses monochromatic or polychromatic ray tracing to simulate the eye with different IOLs, calculating modulation transfer function (MTF) values to select the IOL with the highest MTF for optimal implantation, thereby accounting for individual eye characteristics and aberrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If regression-based formulas (SRK, SRK II, SRK/T) are used for IOL power calculation, then the calculation process is simple and quick, but the accuracy deteriorates for eyes with non-normal dimensions or post-refractive surgery
Solution Approach 1:
The patent replaces the empirical regression-based calculation system with a physics-based optical modeling system using ray tracing. Instead of relying on statistical formulas derived from historical data, the system uses monochromatic or polychromatic ray tracing to simulate light propagation through the eye's optical components, providing accurate predictions for both normal and abnormal eye geometries including post-refractive surgery cases
Solution Approach 2:
The patent changes the fundamental parameters used in IOL power calculation from simple biometric measurements (axial length, corneal curvature) used in regression formulas to comprehensive optical parameters including wavefront aberrations, higher-order Zernike coefficients, and detailed corneal topography. This parameter transformation enables accurate modeling of eyes with non-normal dimensions and aberrations
2Ease of operation
If regression formulas derived from historical clinical data are used, then the method is easy to implement, but it fails to account for individual optical aberrations and non-normal eye characteristics
Solution Approach 1:
The patent segments the corneal power into multiple components: anterior corneal surface power, posterior corneal surface power, and their combined effect. This segmentation allows independent measurement and modeling of each surface, enabling accurate calculation for eyes where the corneal geometry has been altered by refractive surgery. The system separately evaluates higher-order aberrations and lower-order aberrations, treating them as distinct optical components
Solution Approach 2:
The patent introduces wavefront aberration measurements and optical modeling as an intermediary between biometric measurements and IOL power calculation. This intermediary layer captures the unique optical characteristics of each patient's eye, including higher-order aberrations and corneal irregularities, providing a bridge that adapts the calculation to individual eye properties rather than applying a one-size-fits-all formula
3Device complexity
If standard regression methods are applied to eyes with significant aberrations, then the calculation remains straightforward, but the emmetropia prediction becomes inaccurate
Solution Approach 1:
The patent replaces the empirical regression calculation system with a physics-based optical modeling system using ray tracing. Instead of relying on statistical formulas derived from historical data, the system uses monochromatic or polychromatic ray tracing to simulate light propagation through the eye's optical components, providing accurate predictions for both normal and abnormal eye geometries including post-refractive surgery cases
Solution Approach 2:
The patent incorporates iterative optimization where the ray tracing model predicts the post-operative refraction, compares it to the desired emmetropic outcome, and adjusts the IOL power selection accordingly. The system uses measured wavefront aberrations and higher-order Zernike coefficients as feedback to refine the optical model and improve prediction accuracy for eyes with significant aberrations
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 provides improved accuracy in predicting optimal IOL power for both normal and non-normal eyes, including those with significant aberrations, by simulating the optical quality and selecting the IOL that maximizes MTF values, leading to better emmetropic vision outcomes.
Implementation Method 1
for each of a plurality of intraocular lenses (IOLs), simulating the subject eye with the intraocular lens (IOL) implanted in accordance with the measuring, performing either monochromatic or polychromatic ray tracing through the surfaces defining the built eye model
Implementation Method 2
Once that position is determined, the preferred power for an IOL to be implanted is calculated by simple paraxial optics, taking into account that the eye can be modeled under this approximation as a two lens system (cornea+IOL) focusing an image on the retina
Data Source
AI summary
Selecting an optimal intraocular lens (IOL) from a plurality of IOLs for implanting in a subject eye, including measuring anterior corneal topography (ACT), axial length (AXL), and anterior chamber depth (ACD) of a subject eye; selecting a default equivalent refractive index depending on preoperative patient's stage or calculating a personalized value or introducing a complete topographic representation if posterior corneal data are available; creating a customized model of the subject eye with each of a plurality of identified intraocular lenses (IOL) implanted, performing a ray tracing through that model eye; calculating from the ray tracing a RpMTF or RMTF value; and selecting the IOL corresponding to the highest RpMTF or RMTF value for implanting in the subject eye.