Interferometric Eye Length Measurement via Fast Displacement
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Solution Overview
Problem
Current low-coherence interferometry methods for measuring the axial length of the human eye face challenges in achieving high speed and precision due to limited sensitivity and measurement range, particularly in non-invasive applications where subjects cannot hold still for extended periods, and increasing light source power is limited by safety regulations.
Innovation Solution
An interferometric apparatus utilizing a low coherence light source, a fast displacement module to rapidly vary the path length within the reference arm, and polarizing beam splitters to minimize scanning range and preserve sensitivity, enabling high-speed and precise measurements by co-propagating a laser for sub-micrometer precision and using rotation-based displacement modules for faster scanning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If Time Domain Interferometry (TDI) is used to achieve large measurement range for non-invasive eye measurements, then measurement range is sufficient, but measurement speed becomes too slow (cannot achieve >10 Hz required for eye measurements)
Solution Approach 1:
The patent implements dynamic scanning by rapidly moving the reference mirror through a galvanometer or voice coil actuator, transforming the static TDI approach into a dynamic system that achieves both large measurement range and high speed. The mirror scans through a range of positions to cover the entire eye length while maintaining measurement speeds greater than 10 Hz.
Solution Approach 2:
The patent changes the scanning speed parameter and light source coherence length to optimize both measurement range and speed. By selecting specific coherence lengths and scanning velocities, the system achieves adequate sensitivity for eye measurements while maintaining the required measurement speed greater than 10 Hz.
2Speed
If Spectral Domain Interferometry (SDI) is used to achieve high speed and sensitivity measurements, then measurement speed and sensitivity are improved, but measurement range becomes too small for non-invasive eye measurements
Solution Approach 1:
The patent segments the measurement process into multiple sequential scans across different reference mirror positions. Each scan covers a portion of the eye length, and by combining data from multiple scans, the system achieves both the high speed/sensitivity of SDI and the large measurement range required for eye measurements.
Solution Approach 2:
The system uses dynamic reference mirror scanning to extend the measurement range beyond what a single SDI measurement can provide. The mirror moves through multiple positions, allowing the system to cover the entire eye length while maintaining the high speed and sensitivity characteristics of SDI.
3Measurement precision
If light source power is increased to improve measurement sensitivity and speed, then sensitivity and speed are improved, but eye safety regulations are violated
Solution Approach 1:
The patent optimizes the light source coherence length and spectral bandwidth parameters to achieve adequate sensitivity without increasing power. By selecting appropriate coherence lengths that match the eye's optical path differences, the system achieves sufficient signal strength while maintaining safe illumination levels.
Solution Approach 2:
The patent replaces power-based sensitivity enhancement with interferometric signal processing techniques. Through coherent detection and signal averaging, the system achieves high sensitivity using low-power light sources that comply with eye safety regulations.
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
The apparatus achieves high-speed axial eye length measurements at 15 Hz with sufficient sensitivity and precision, maintaining safety standards by optimizing light usage and reducing unnecessary scanning, allowing for accurate measurement of the entire eye length with minimal light loss.
Implementation Method 1
Low-coherence interferometry (LCI) is a powerful non-contact measurement technique. It is used to interferometrically measure and characterize weak scattering signals using low-coherence light.
Implementation Method 2
a fast displacement module for rapidly varying the path length within a reference arm of an interferometer
Implementation Method 3
An optical probe comprised of a first polarizing beam splitter and a second polarizing beam splitter positioned to provide two polarized beams having differing path lengths
Implementation Method 4
a laser directing a laser beam that is co-propagating with light from the low coherence light source into the displacement module
Data Source
AI summary
An apparatus for measuring the axial length of a human eye, the apparatus comprising a low coherence light source; a beam splitter; a fast displacement module for rapidly varying the path length within a reference arm of an interferometer; a laser directing a laser beam that is co-propagating with light from the low coherence light source into the displacement module.