Harmonic Laser Depth Measurement for Corneal Tissue
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Solution Overview
Problem
Conventional corneal shape corrective surgeries face challenges in accurately measuring corneal depths, particularly in incising below Bowman's layer, leading to potential deep incisions into the stroma and interference with vision correction due to irregular corneal thickness profiles.
Innovation Solution
A laser-based system that focuses a pulsed laser beam with energy below the photodisruption threshold to generate harmonics, allowing for precise detection of tissue layer transitions within the cornea, enabling accurate depth measurements and incision calibration to maximize stromal preservation during vision correction procedures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a predetermined constant depth incision is made based on population average corneal thickness, then the incision procedure is simplified and can be performed efficiently, but the measurement precision and manufacturing precision deteriorate due to irregular corneal thickness profiles, resulting in potentially deep incisions into the stroma
Solution Approach 1:
The system changes the parameter of laser beam energy from below photodisruption threshold (for measurement) to above threshold (for incision). The measurement mode uses low energy to generate harmonics for detecting tissue layer transitions, while the incision mode uses high energy to cut tissue. This allows the same laser system to perform both precise measurement and effective incision without mechanical changes.
Solution Approach 2:
The system uses feedback from harmonic signal detection to determine tissue layer transitions and adjust the incision depth. The measured corneal thickness and layer transition positions feed back to the control system, which then calculates the precise incision depth needed to create a flap of optimal thickness, replacing the predetermined constant depth approach.
2Strength
If the laser beam energy is increased to ensure effective tissue incision, then the incision effectiveness is improved, but the measurement precision deteriorates due to photodisruption of the corneal tissue
Solution Approach 1:
The system uses periodic pulsed laser action with different energy levels. Measurement pulses are delivered at low energy (below photodisruption threshold) to detect harmonic signals from tissue layers. After measurement is complete, the system switches to high energy pulses for incision. The periodic pulsing allows thermal management and prevents unintended photodisruption during measurement while ensuring effective cutting during incision.
Solution Approach 2:
The laser system dynamically changes the energy parameter based on the operational phase. During the measurement phase, energy is kept below the photodisruption threshold to allow harmonic generation without tissue damage. During the incision phase, energy is increased above the threshold to achieve effective tissue cutting. This parameter change resolves the contradiction between measurement precision and incision effectiveness.
3Reliability
If a buffer depth is added to the predetermined incision depth to account for corneal thickness variation, then the reliability of stromal preservation is improved, but the manufacturing precision deteriorates by incising more stromal tissue than needed
Solution Approach 1:
The system performs preliminary measurement of the actual corneal thickness and layer structure using harmonic detection before performing the incision. This preliminary action provides accurate information about the specific patient's corneal anatomy, allowing the incision depth to be precisely calculated to achieve the desired flap thickness without needing to add a conservative buffer that would remove excess stroma.
Solution Approach 2:
The incision depth parameter is dynamically adjusted based on the measured corneal thickness and layer transition positions. Instead of using a fixed predetermined depth with buffer, the system calculates the optimal incision depth as: measured epithelium thickness + measured Bowman's layer thickness + desired flap thickness. This parameter adjustment based on real measurement data achieves both reliability of stromal preservation and manufacturing precision of flap thickness.
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 precise depth measurements and incisions, maximizing the preservation of stromal tissue for effective vision correction by accurately locating tissue layers and calibrating the laser system, thereby improving the accuracy of corneal flap formation.
Implementation Method 1
A. Brocas et al., 'Corneal Imaging by second and third harmonic generation microscopy'
Implementation Method 2
A. Brocas et al., 'Corneal Imaging by second and third harmonic generation microscopy'
Implementation Method 3
A laser beam is focused to a laser spot having an energy below a photodisruption threshold of the cornea
Data Source
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AI summary
Systems, apparatus, and methods are disclosed for locating tissue layer transitions within a cornea, including focusing a laser to a laser spot with an energy below a photodisruption threshold of the cornea, varying a position of the focal spot of the laser between an anterior surface of the cornea and a posterior surface of the cornea, and determining one or more transitions of the tissue layers based on a change in harmonic light generated by the laser spot.