OCT Pachymetry Map Alignment Using Corneal Vertex Tracking
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Solution Overview
Problem
Current Optical Coherence Tomography (OCT) systems face challenges in accurately aligning scan lines with the eye's position due to decentration and eye movement, leading to errors in corneal thickness measurements and image artifacts, especially during prolonged scan durations.
Innovation Solution
The method involves using pairs of crossed B-scans to detect and correct misalignment by identifying the corneal vertex, adjusting scan lines to register the Pachymetry map accurately, and employing a specific scan pattern to minimize motion artifacts, while also detecting and correcting eye motion through measurement data analysis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional alignment methods are used to position the eye, then initial alignment can be achieved, but alignment accuracy deteriorates during prolonged scan durations due to eye movement and decentration
Solution Approach 1:
The system performs preliminary identification of the corneal vertex and establishes a reference position before the main scanning process. This preliminary action creates a baseline alignment that compensates for subsequent eye movements during prolonged scans, maintaining measurement precision throughout the scan duration.
Solution Approach 2:
The system continuously monitors eye position by tracking the corneal vertex across multiple B-scans and provides feedback to adjust the scan line alignment. This real-time feedback mechanism corrects for eye movements and decentration that occur during prolonged scanning, preventing alignment accuracy deterioration.
2Productivity
If scan lines are not properly aligned with the eye's position, then scanning can proceed without interruption, but measurement errors increase in corneal thickness
Solution Approach 1:
The system performs preliminary identification of the corneal vertex position and calculates the optimal scan line configuration before acquiring measurement data. This preliminary alignment ensures that scan lines are properly positioned relative to the corneal apex, preventing measurement errors while maintaining scanning efficiency throughout the procedure.
Solution Approach 2:
The system dynamically adjusts scan line alignment based on the identified corneal vertex position and detected eye movements. Rather than using fixed alignment, the scan parameters are continuously adapted to match the actual eye position, maintaining measurement precision without interrupting the scanning process.
3Device complexity
If decentration is not corrected, then the imaging process remains simple, but errors in Pachymetry map increase significantly
Solution Approach 1:
The system performs preliminary detection and correction of decentration by identifying the corneal vertex position and adjusting the scan pattern accordingly. This preliminary correction prevents the accumulation of errors in the Pachymetry map while adding minimal complexity to the imaging process through automated vertex detection algorithms.
Solution Approach 2:
The system replaces manual mechanical alignment adjustments with automated optical detection and computational correction of decentration. By using image processing algorithms to detect the corneal vertex and calculate correction parameters, the system achieves accurate Pachymetry mapping without complex mechanical alignment mechanisms.
4Device complexity
If eye motion is not tracked and corrected, then the system operates without additional tracking components, but image artifacts increase
Solution Approach 1:
The OCT imaging system performs multiple functions using the same measurement data: it both acquires corneal thickness information and tracks eye motion by analyzing the position of the corneal vertex across sequential B-scans. This multi-functionality enables eye motion tracking without adding separate tracking components, reducing system complexity while minimizing image artifacts.
Solution Approach 2:
The system uses feedback from the OCT measurement data itself to detect eye motion by monitoring changes in corneal vertex position between scans. This feedback mechanism enables real-time detection and correction of eye-induced artifacts without requiring additional sensors or tracking systems, maintaining simple system architecture.
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 significantly reduces measurement errors, achieving repeatability of ≤5 μm in central zones and ≤10 μm in radial zones for Pachymetry map measurements, and minimizes image artifacts by accurately aligning scan lines with the eye's position.
Implementation Method 1
The OCT device uses a light source to illuminate a sample and an interferometer and detector to measure the path length to a reflector in the sample by interference between the light reflected from the sample and a reference light beam
Data Source
AI summary
A method and apparatus for imaging within the eye is provided whereby a component of eye position is detected using optical imaging data. Tracking eye position over time and correctly registering imaging data for scan locations or using eye position to detect decentration achieves improved imaging. In one embodiment, essentially perpendicular B-scans are imaged sequentially and the corneal arc within each B-scan is analyzed to determine the vertex of the eye. The eye vertex is tracked over pairs of perpendicular B-scans to determine eye motion. In another embodiment, the decentration in the Pachymetry map is removed by correcting for the misalignment of the center of the Pachymetry map and the actual location of the corneal vertex.