Swept Source Optical Coherence Reflectometry for Intraocular Distance
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Solution Overview
Problem
Current methods for measuring intraocular distances in the eye, such as Swept Source Optical Coherence Domain Reflectometry (SS OCDR), face challenges in achieving high accuracy and speed due to eye movements, leading to signal distortion and measurement errors, especially when active tracking methods result in latency issues.
Innovation Solution
A device utilizing a tunable laser source with a spectral line width of less than 168 m^-1 and a tuning time adapted to minimize sample displacements during measurement, allowing for accurate distance measurement across the entire eye length without active tracking, using a device with a measuring beam diameter of less than 3 mm and a wavelength between 600 and 1150 nm, and incorporating a reference interferometer for calibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If a Michelson interferometer with mechanical reference mirror adjustment is used, then the measuring range can cover more than 43 mm, but the measurement time increases to several seconds making the patient unable to blink
Solution Approach 1:
The patent replaces the mechanical reference mirror adjustment system with a swept source optical system. Instead of mechanically moving the reference mirror to scan through different path lengths, the invention uses a tunable laser source that sweeps through a range of wavelengths, with the optical path length information encoded in the spectral domain. This substitution of mechanical movement with optical frequency modulation dramatically reduces measurement time while maintaining the full measuring range capability.
Solution Approach 2:
The invention changes the fundamental measurement parameter from mechanical position (reference mirror displacement) to optical wavelength (laser tuning frequency). By sweeping the laser wavelength across a defined range and detecting the interference pattern in the spectral domain, the system achieves the same path length measurement capability without mechanical movement, thereby eliminating the time constraint that prevented patients from blinking during measurement.
2Measurement precision
If active tracking methods are used to compensate for eye movements, then measurement accuracy can be maintained, but latency errors occur due to finite tracking system response time
Solution Approach 1:
The patent employs the eye's own optical structures (cornea, lens, retina) as built-in reference markers for movement compensation. By detecting the positions of these anatomical landmarks in the spectral interferogram, the system automatically references all measurements to the actual eye position, eliminating the need for external tracking systems. The eye essentially serves its own reference function, providing real-time movement compensation without any latency.
Solution Approach 2:
The invention converts the previously harmful effect of eye movements (which caused measurement errors) into a useful reference signal. By using the eye's anatomical structures as internal references within the spectral domain, the system transforms movement-induced signal variations into valuable positional information that automatically compensates for eye motion, turning a source of error into a correction mechanism.
3Measurement precision
If a broader spectral tuning range is used, then measurement accuracy improves, but the line width must be reduced which increases the tuning time
Solution Approach 1:
The patent applies partial action by selecting an optimized spectral tuning range that provides sufficient measurement accuracy without requiring the maximum possible bandwidth. By choosing a tuning range that is adequate rather than excessive, and combining it with a correspondingly optimized line width, the system achieves the necessary precision while maintaining practical tuning speeds suitable for clinical measurement requirements.
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 accurate intraocular distance measurements with an accuracy better than 100 μm, robust against typical eye movements, and capable of simultaneous distance measurements between the cornea, lens, and retina, reducing signal losses and errors.
Implementation Method 1
a laser light source, the tuning of the light source being changed around a centroid wave number k0
Implementation Method 2
The functional principle is based on what is known as time domain optical coherence domain reflectometry, a short-coherence interferometry method... The main component is a Michelson interferometer, which enables the detection of interference from the light scattered back from the cornea, lens and retina
Implementation Method 3
at least one receiver for the light scattered back from the sample, with the sample being illuminated via a coupling device with a measuring beam of diameter D on the sample surface
Data Source
Figure 1a~1c
Figure 2a~2d
Figure 3a~3e
AI summary
The invention relates to a device for Swept Source Optical Coherence Domain Reflectometry (SS OCDR) on moving samples, in particular human eyes, for obtaining A-scans with a measuring range corresponding to the sample length, with a laser light source tunable by a center-of-mass wavenumber ko and at least one receiver for the light backscattered from the sample, wherein the sample is illuminated on the sample surface via a coupling device with a measuring beam of diameter D, the light source has a spectral linewidth δk<168m-1 and the tuning of the light source takes place in τ < 44s / (D*k0).