Ophthalmic Ranging with Specular-Highlight Spatial Mapping
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Solution Overview
Problem
Conventional ophthalmic ranging instruments struggle with accurate distance measurement when images become de-focused, as specular highlights obscure pupil centers, reducing reliability and requiring narrow depth-of-field alignment, especially with CMOS sensors and fixed focal length lenses.
Innovation Solution
An ophthalmic apparatus using an illumination device to create a specular highlight with varying spatial distribution in the image, processed by a processor to determine distance, and a movement mechanism to adjust position for predefined ranges, complemented by stereoscopic ranging techniques for fine alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If conventional stereo range-finding devices use IR light sources to illuminate the eye, then the eye can be illuminated for imaging, but specular highlights are produced that obscure the pupil edge and make distance measurement unreliable
Solution Approach 1:
The patent converts the harmful specular highlights into useful distance measurement information. Instead of treating the highlights as obstacles that obscure pupil centers, the system uses the spatial distribution characteristics of these highlights (such as their separation distance or size) as the primary basis for determining distance to the eye, thereby transforming a measurement obstacle into a measurement resource.
2Device complexity
If fast lenses of fixed focal length are used with CMOS sensors, then the device complexity is reduced, but the depth-of-field becomes narrow requiring precise alignment
Solution Approach 1:
The patent replaces the mechanical alignment system (which would require precise physical positioning and focusing mechanisms) with an optical-processing solution. By using the spatial distribution of specular highlights as the measurement basis and processing images computationally, the system achieves reliable distance measurement without requiring narrow depth-of-field or complex mechanical alignment mechanisms.
3Adaptability or versatility
If stereo images become de-focused, then the device can operate over a wider distance range, but the accuracy of distance measurement decreases
Solution Approach 1:
The patent changes the measurement parameter from pupil center location (which requires focused images) to specular highlight spatial distribution characteristics (such as highlight separation or size). This parameter change allows distance measurement to be performed reliably on defocused images, thereby expanding the operational distance range while maintaining measurement accuracy.
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
Enhances distance measurement reliability by leveraging specular highlights, reducing hardware complexity and improving image quality through resilient distance estimation and precise alignment, even in defocused conditions.
Implementation Method 1
the image of the eye comprises a specular highlight from the illumination device
Data Source
AI summary
An ophthalmic apparatus arranged to determine a distance between the ophthalmic apparatus and an eye, the ophthalmic apparatus comprising: an illumination device which illuminates the eye; an imaging device which acquires an image of the eye, wherein the illumination device and the imaging device are arranged such that the image of the eye comprises a specular highlight from the illumination device having a spatial distribution in the image which varies with the distance between the ophthalmic apparatus and the eye; and a processor arranged to: process the image to determine a value of an indicator which is indicative of a property of the spatial distribution; and use the determined value of the indicator and a mapping which maps values of the indicator to corresponding values of the distance between the ophthalmic apparatus and the eye to determine the distance between the ophthalmic apparatus and the eye.