OCT Eye Tomogram Registration With Extended Depth of Field
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Solution Overview
Problem
Existing optical coherence tomography (OCT) techniques struggle to accurately measure total eye shape due to limitations in depth of field, eye movement, and registration issues, particularly in measuring eye length and registering lateral and axial positions, leading to incomplete or inaccurate optical property calculations for intra-ocular lens surgery planning.
Innovation Solution
The method involves acquiring and processing multiple optical coherence tomograms within a single frame using a two-dimensional sensor array, with overlapping regions on the anterior surface of the eye, and employing a compound reflector to impose a predetermined optical path length difference, allowing for rapid registration and compensation for axial separation, thereby enhancing the depth of field and registration accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a broad source bandwidth is used to provide short coherence length for depth resolution, then depth resolution is improved, but the depth range over which the sample beam can interfere with the reference beam is limited
Solution Approach 1:
The patent divides the reference beam into multiple portions with different optical path lengths by introducing a first reference path and a second reference path with different lengths. This segmentation allows each path to interfere with specific depth ranges of the sample beam, enabling extended depth range measurement while maintaining depth resolution through the broadband source.
2Length of stationary object
If multiple reference paths are provided to extend axial depth, then depth range is improved, but the system complexity increases
Solution Approach 1:
The patent combines multiple reference paths (first reference path and second reference path with different lengths) into a single interferometric system that processes both paths simultaneously. The sample beam interferes with both reference paths, and the resulting signals are processed to extract information from different depth ranges, achieving extended axial depth without proportionally increasing system complexity.
3Loss of information
If measurements are taken over extended periods to capture eye movement, then completeness of data is improved, but measurement accuracy deteriorates due to eye movement
Solution Approach 1:
The patent performs rapid sequential measurements of the eye at multiple positions within a single exposure period. By capturing data from different eye positions quickly and then registering these positions to a common reference frame, the system maintains measurement accuracy while achieving data completeness across extended areas, preventing eye movement artifacts.
4Measurement precision
If lateral and axial positions are registered accurately, then measurement precision is improved, but the difficulty of computing optical properties increases
Solution Approach 1:
The patent uses the registered lateral and axial positions as feedback information to compute optical properties of the eye. The registration data from multiple eye positions is fed into computational models that calculate optical properties such as refractive index and curvature, enabling accurate determination of these properties while managing computational complexity through efficient algorithms.
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 enables precise measurement of total eye shape with improved registration, providing accurate optical properties for surgical planning, such as optical power and astigmatism, by overcoming crosstalk and eye movement challenges.
Implementation Method 1
optical coherence tomography (OCT) is a widely used interferometric technique for studying biological samples including in vivo tissue such as the human eye
Data Source
AI summary
Methods and apparatus are provided for optical coherence metrology or tomography across an extended area of an eye with improved registration. At least two optical coherence tomograms are acquired, with each tomogram containing data from regions of an anterior surface of the eye that are at least partially overlapping, and data from one or more deeper structures such as the retina or the anterior or posterior lens surfaces. The tomograms are then processed to register the data from the overlapping portions of the anterior surface regions, thereby registering the data from the deeper structures. In certain embodiments the reference arm of the apparatus comprises a compound reflector having at least two axially separated reflective surfaces for applying differential delays to different portions of the reference beam. The depth of field of the apparatus is thereby extended to enable measurement of eye length. In certain embodiments eye length measurements at a number of angles of incidence provide information on total eye shape.