Smartphone-Based Inverse Shack-Hartmann Refractive Error Measurement
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Solution Overview
Problem
Existing handheld consumer devices for self-refraction are not as accurate, easy to use, or economical as they need to be for measuring refractive properties of optical systems, particularly the human eye, due to limitations in current technologies like the method described in US 2013/0027668 A1.
Innovation Solution
The use of the inverse Shack-Hartmann technique, combined with a smartphone as a light source, to simulate an optometrist's cross-cylinder examination by displaying two parallel lines that the user adjusts until they are aligned, allowing for high-resolution measurements of refractive errors using the device's screen and lenslets, which can include micro-lens arrays or pinhole arrays.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single multi-lens array or pinhole array is used for refractive measurement, then the device structure is simplified, but measurement precision deteriorates
Solution Approach 1:
The patent divides the optical system into multiple lenslets arranged in a grid pattern, where each lenslet independently focuses light from different portions of the display. This segmentation allows simultaneous measurement of multiple meridians and improves measurement precision while maintaining a relatively simple overall device structure.
Solution Approach 2:
The patent transitions from one-dimensional line measurements to two-dimensional area measurements by using a multi-lens array that captures light from multiple directions simultaneously. This dimensional expansion enables comprehensive refractive error assessment including astigmatism measurements from multiple meridians.
2Measurement precision
If high-resolution measurement is achieved using smartphone displays, then measurement precision improves, but device complexity increases
Solution Approach 1:
The patent makes the smartphone display serve multiple functions: it acts as both the light source and the measurement target. The display shows parallel lines that are simultaneously used for alignment reference and for generating the measurement pattern, eliminating the need for separate light sources and target objects.
Solution Approach 2:
The optical system is designed to use the smartphone's own display components for measurement, making the device self-sufficient. The display generates the measurement pattern and provides the reference lines, so the system measures itself without requiring external calibration tools or additional components.
3Measurement precision
If the cross-cylinder procedure is simulated for accurate refraction measurement, then measurement precision improves, but ease of operation deteriorates
Solution Approach 1:
The patent implements real-time visual feedback by displaying the separation distance between parallel lines on the smartphone screen. As the user adjusts the device or their focus, the system continuously updates the display to show whether the lines are aligned or separated, guiding the user toward the correct measurement position without requiring complex manual adjustments.
Solution Approach 2:
The patent introduces a software intermediary that processes the optical measurements and translates them into user-friendly visual indicators. The application on the smartphone acts as a mediator between the complex optical system and the user, converting raw measurement data into intuitive visual feedback about line alignment and separation.
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 method provides a more accurate and user-friendly way to assess refractive errors by leveraging high-resolution smartphone displays and optical systems, enabling precise detection of refractive errors and allowing for simultaneous measurement of multiple meridians, thereby improving visual acuity and reducing noise in astigmatism measurements.
Implementation Method 1
The optical input of a disclosed device can originate from a smart phone, personal electronic device or other optical system... After the light passes through the optical system, at the imaging plane two lines are formed
Implementation Method 2
The coma, or comatic aberration, in an optical system referring to an aberration inherent to certain optical designs or due to imperfection in the lens or other components that results in off-axis point sources such as pixels forming a line are appearing distorted, appearing to have a tail (coma) like a comet
Implementation Method 3
In refractive or diffractive optical systems, especially those imaging a wide spectral range, coma can be a function of wavelength, in which case it is a form of chromatic aberration
Data Source
AI summary
Disclosed embodiments may include a device, system and method for providing a low cost device that can measure refractive errors very accurately via attachment to a smart phone. A disclosed device may use ambient light or a light source in simulating the cross cylinder procedure that optometrists use by utilizing the inverse Shack-Hartman technique. The optical device may include an array of lenslets and pinholes that will force the user to effectively focus at different depths. Using an optical device, in conjunction with a smart phone, the user first changes the angle of the axis until he/she sees a cross pattern (the vertical and horizontal lines are equally spaced). The user adjusts the display, typically using the controls on the smartphone, to make the lines come together and overlap, which corresponds to bringing the view into sharp focus, thus determining the appropriate optical prescription for the user.