Corneal Topography Measurement Using Confocal Interferometry
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Solution Overview
Problem
Current corneal topography methods face challenges in accuracy and reproducibility, particularly with long scanning times and eye movement issues, and existing OCT systems struggle to provide reliable topography data with high resolution and precision.
Innovation Solution
A confocal, interferometric measurement arrangement using a frequency domain OCT method focuses illumination radiation on the cornea's center of curvature, employing a beam splitter and reference light source with a delay line to enhance spatial resolution and accuracy, allowing for simultaneous recording of interference patterns and distance measurements to determine topography.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If OCT procedures use long scanning times to achieve high-resolution topography data, then measurement precision is improved, but eye movement artifacts increase and reproducibility deteriorates
Solution Approach 1:
The patent employs periodic action by using a high-speed tunable laser source that rapidly sweeps through wavelengths in a periodic manner, enabling the acquisition of multiple A-scans and B-scans in quick succession. This periodic wavelength sweeping allows the system to capture topography data before eye movements significantly alter the corneal position, thereby maintaining both high precision and reproducibility
Solution Approach 2:
The system performs preliminary action by acquiring multiple B-scans rapidly in sequence before eye movements can significantly affect the measurement. By collecting multiple data sets in advance and processing them together, the system can determine topography parameters with high precision while compensating for minor eye movements that occur during the scanning period
2Device complexity
If traditional topography methods use placidoring projection or keratometers, then device complexity is reduced, but measurement precision and accuracy of corneal topography deteriorates
Solution Approach 1:
The patent applies universality by designing an OCT system that can perform multiple functions: it measures both the topography of the cornea and the axial length of the eye using the same interferometric setup. The same tunable laser source, beam splitter, and detector array used for topography can also acquire biometric data, reducing the need for separate specialized devices while maintaining high precision
Solution Approach 2:
The system replaces mechanical contact-based methods (keratometers requiring contact with the cornea) with a non-contact optical interferometric system. The OCT uses light interference patterns to measure corneal surface geometry without touching the eye, eliminating mechanical complexity while achieving superior measurement precision through optical phase detection
3Device complexity
If OCT systems use time domain procedures to measure corneal topography, then device complexity is reduced, but measurement precision and scanning speed deteriorates
Solution Approach 1:
The patent implements periodic action through a rapidly tunable laser source that sweeps through wavelengths in a periodic fashion, enabling the system to acquire multiple lines of data per second. This high-speed periodic wavelength modulation allows the Fourier domain OCT to process information much faster than time domain methods, achieving scanning speeds suitable for clinical topography applications
Solution Approach 2:
The system applies dynamics by using a tunable laser source with rapidly changing wavelength rather than a fixed wavelength source. The dynamic adjustment of the laser wavelength during the measurement process enables the Fourier domain processing to extract topography information from interference patterns, significantly increasing scanning speed compared to static time domain approaches
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 achieves high-resolution, accurate topography with improved reproducibility, enabling precise determination of corneal curvature and wavefront deviations, even in aspherical corneas, with accuracy of ±5μm and reduced scanning time.
Implementation Method 1
the illumination radiation is focused on the center of curvature of the cornea
Implementation Method 2
the light signals reflected by the cornea are detected both by the confocal, interferometric measurement arrangement
Implementation Method 3
the part of the light signal reflected by the cornea decoupled by a beam splitter and imaged to the spatial resolution detector is superimposed with a reference signal generated by a reference light source with a delay line
Data Source
Figure 1
AI summary
The arrangement consists of a confocal, interferometric measurement arrangement, a spatially resolving detector, apparatuses for positioning and an evaluation unit. A beam splitter that is present serves to output couple and image part of the light signal reflected by the cornea onto the spatially resolving detector, in front of which a reference light source with a delay line and a beam splitter are arranged in order to realize a superimposition of a reference signal on the part of the light signal reflected by the cornea that is to be imaged on the spatially resolving detector. The evaluation unit is embodied to determine the topography of the cornea from the signals of the interferometric measuring arrangement and of the spatially resolving detector, which are recorded at the same time. The proposed solution combines a confocal FD-OCT method with elements of imaging holoscopy and, as a result thereof, can measure the topography of the cornea by interferometry with the necessary accuracy, in particular in already established systems, such as the IOLMaster® 700 by Zeiss.