Corneal Topography Measurement Using Segmented Light Sources
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Solution Overview
Problem
Conventional Placido disk type corneal topographers face challenges in detecting the central region of the cornea, suffer from alignment errors, and fail to adequately measure skew rays, which limits their ability to accurately characterize ocular aberrations and corneal topography.
Innovation Solution
A system using a combination of first and second light sources, where second light sources are located at optical infinity and the detector array is at a telecentric position, allowing for accurate measurement of the central region and providing a uniform grid of spots on the detector array, while also determining vertex alignment errors to correct for misalignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an aperture is provided in the Placido disk to pass light from the cornea to the detector array, then light transmission is enabled, but the central region of the cornea cannot be detected
Solution Approach 1:
The system divides the light source into two separate groups: first light sources arranged around a central axis at a radial distance defining an aperture, and second light sources positioned to illuminate the central corneal region. This segmentation allows each light source group to serve a specific measurement function without interfering with the other, enabling both peripheral and central corneal topography to be measured simultaneously through the same aperture.
2Use of energy by moving object
If the aperture size is increased to improve light transmission, then more light reaches the detector, but the problem of central region detection is exacerbated
Solution Approach 1:
The system applies different measurement approaches to different regions of the cornea. First light sources are positioned to measure peripheral corneal regions by reflecting off the corneal surface, while second light sources are positioned to measure the central corneal region. Each light source group is optimized for its specific region, allowing the aperture to be sized for adequate light transmission without compromising central region measurement capability.
3Measurement precision
If vertex error is not corrected, then alignment errors occur between the corneal surface vertex and the design corneal vertex plane, but correcting for vertex error adds computational complexity
Solution Approach 1:
The system performs preliminary measurement of the actual corneal vertex position using the first light sources before conducting the main topography measurement. By determining the vertex position in advance, the system can pre-calculate the vertex error and apply the appropriate correction factor to subsequent measurements, simplifying the overall computational process while maintaining high measurement accuracy.
4Measurement precision
If Placido rings are used to measure corneal topography, then radial deviations can be detected, but skew rays in the azimuthal direction cannot be adequately measured
Solution Approach 1:
The system combines two measurement approaches: Placido ring reflection from first light sources for measuring radial deviations, and direct imaging of second light sources for capturing skew ray information. By merging these two methods into a single integrated system, both radial and azimuthal corneal abnormalities can be detected, providing comprehensive corneal topography measurement capability.
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
Enables comprehensive characterization of the entire corneal topography, including the central region, and improves the accuracy of ocular aberration measurements by addressing alignment issues and measuring skew rays, thereby enhancing the precision of corneal topography and aberration analysis.
Implementation Method 1
A Placido disk system consists of a series of concentric illuminated rings that are reflected off the cornea and viewed with a detector array
Implementation Method 2
an optical system adapted to provide light from the second light sources through the aperture to a cornea of an eye, and to provide images of the first light sources and images of the second light sources from the cornea
Implementation Method 3
the second light sources are disposed to be in an optical path approximately one focal length, f, away from the optical element
Data Source
Figure 1A
Figure 1B~1C
Figure 1D
AI summary
A system measures a corneal topography of an eye. The system includes a group of first light sources arranged around a central axis, the group being separated from the axis by a radial distance defining an aperture in the group; a plurality of second light sources; a detector array; and an optical system adapted to provide light from the second light sources through the aperture to a cornea of an eye, and to provide images of the first light sources and images of the second light sources from the cornea, through the aperture, to the detector array. The optical system includes an optical element having a focal length, f. The second light sources are disposed to be in an optical path approximately one focal length,/, away from the optical element.