Custom Chromatic Adjustment for Eye Refraction Measurement
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Solution Overview
Problem
Current optical measurement instruments, such as aberrometers, use a standard Chromatic Adjustment Factor (CAF) of 0.7 to convert infrared refraction measurements to visible refraction, but this results in errors for about 20% of subjects, as the correct CAF varies with individual eye parameters like corneal and lens refractive index changes between wavelengths.
Innovation Solution
A method and system that use Purkinje images at different wavelengths to determine customized chromatic adjustment factors for each eye by measuring parameters like corneal curvature and lens thickness, allowing for precise correction of infrared refraction measurements to visible spectrum refraction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a standard Chromatic Adjustment Factor (CAF) of 0.7 is used to convert infrared refraction to visible refraction, then the average calculated visible refraction agrees with average manifest refraction, but about 20% of subjects have errors greater than 0.5 diopters
Solution Approach 1:
The patent applies local quality by transitioning from a uniform chromatic adjustment factor applied to all subjects to individualized chromatic adjustment factors tailored to each subject's specific ocular parameters. The system measures subject-specific parameters (axial length, corneal curvature, lens properties) and calculates customized CAF values, ensuring that each subject receives the precise adjustment needed for their unique eye characteristics, thereby eliminating the 0.5+ diopter errors experienced by 20% of subjects with standard CAF
Solution Approach 2:
The patent implements parameter changes by using measured ocular parameters (axial length, corneal curvature radius, lens thickness, refractive indices at different wavelengths) to dynamically calculate and adjust the chromatic adjustment factor. Instead of using a fixed CAF of 0.7, the system varies the CAF based on changes in these physical parameters across different subjects, allowing the refraction conversion to adapt to individual anatomical and optical variations
2Measurement precision
If individual chromatic adjustment factors are calculated based on subject-specific parameters, then refraction accuracy improves, but measurement complexity and processing requirements increase
Solution Approach 1:
The patent applies segmentation by dividing the chromatic adjustment process into distinct measurement and calculation components. The system separately measures axial length, corneal curvature, and lens parameters using dedicated optical subsystems, then processes these measurements through a structured algorithm that calculates the customized CAF and applies it to convert infrared refraction to visible refraction. This segmented approach manages complexity by organizing the measurement and calculation tasks into modular, manageable steps
Solution Approach 2:
The system implements self-service by automatically measuring all necessary ocular parameters and calculating the customized chromatic adjustment factor without requiring manual intervention. The optical measurement instrument performs complete data collection, processes the measurements through embedded algorithms, and generates the corrected visible refraction value autonomously, reducing the need for external calibration or manual adjustment while maintaining high precision
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 significantly reduces errors in refraction calculations, providing more accurate visible refraction measurements that align with manifest refractions determined by optometrists, improving the accuracy of eyeglass prescriptions.
Implementation Method 1
An aberrometer may include a Shack-Hartmann wavefront sensor, which may measure the values for one or more refraction orders of a subject's eye from a light wavefront which is returned from the eye.
Implementation Method 2
capturing at least two different Purkinje images at two different corresponding wavelengths from at least one surface of the lens of the subject's eye
Data Source
AI summary
An optical measurement system method for measuring a characteristic of a subject's eye use a probe beam having an infrared wavelength in the infrared spectrum to measure a refraction of the subject's eye at the infrared wavelength; capture at least two different Purkinje images at two different corresponding wavelengths from at least one surface of the lens of the subject's eye; determine from the at least two different Purkinje images a value for at least one parameter of the subject's eye; use the value of the at least one parameter to determine a customized chromatic adjustment factor for the subject's eye; and correct the measured refraction of the subject's eye at the infrared wavelength with the customized chromatic adjustment factor to determine a refraction of the subject's eye at a visible wavelength in the visible spectrum.