Iris Registration for Astigmatism Axis Alignment in Laser Cataract Surgery
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Solution Overview
Problem
Existing ophthalmic laser systems face challenges in accurately determining the orientation of astigmatism in a patient's eye due to cyclorotation and docking-induced rotation, leading to inaccurate alignment during cataract procedures.
Innovation Solution
A laser ophthalmic system that uses a camera to capture undocked and docked iris images, applies a parameterized transformation to correct for rotation, dilation, and translation, and optimizes these parameters using a gradient Newton-Raphson method to accurately align the astigmatism axis for precise laser delivery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the eye is mechanically coupled to the patient interface device for cataract procedure, then the laser procedure can be performed, but the orientation of corneal astigmatism changes due to cyclorotation and docking-induced rotation
Solution Approach 1:
The system captures an undocked iris image before the eye is mechanically coupled to the patient interface device. This preliminary image serves as a reference to later calculate the rotation angle after docking, allowing the system to pre-establish the relationship between the undocked and docked coordinate frames before the astigmatism measurement becomes invalid
Solution Approach 2:
The system creates a digital copy of the iris pattern from the undocked image and transforms it using the calculated rotation angle to generate a virtual docked iris image. This copied and transformed iris pattern is then used to register the astigmatism axis orientation without requiring physical contact with the cornea, thus preserving measurement accuracy while enabling procedure performance
2Measurement precision
If astigmatism is measured when the eye is free of mechanical contact, then accurate astigmatism measurement is achieved, but the orientation may differ from the docked eye orientation
Solution Approach 1:
The system uses feedback from the undocked iris image to calculate the rotation angle that occurs during docking. This feedback mechanism allows the system to automatically adjust for orientation changes by transforming the astigmatism axis based on the measured rotation, eliminating the need for manual realignment and ensuring the corrected orientation matches the docked eye position
Solution Approach 2:
The system changes the parameter of interest from the raw astigmatism axis orientation to the rotated astigmatism axis orientation by applying a rotation transformation. This parameter transformation converts the measurement taken in the undocked state into the corresponding orientation in the docked state, resolving the information mismatch without requiring re-measurement
3Ease of operation
If conventional visual evaluation and manual ink marks are used to register astigmatism axis, then the process is simple, but the alignment accuracy is insufficient due to eye rotation
Solution Approach 1:
The system replaces the manual mechanical process of visual evaluation and ink marking with an automated image processing system. The computer captures iris images, calculates rotation angles through coordinate transformation, and automatically determines the corrected astigmatism axis orientation, eliminating human error and providing superior alignment accuracy while maintaining ease of operation through automation
Solution Approach 2:
The system transitions from two-dimensional manual marking on the eye surface to three-dimensional coordinate space transformation by capturing iris images in the optical path and applying mathematical rotation transformations. This dimensional approach allows precise calculation of the rotation angle and accurate registration of the astigmatism axis without the limitations of manual surface marking
Data Source
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AI summary
In a laser cataract procedure that also corrects for astigmatism, an iris registration method compares an iris image of a patient's eye taken when the eye is not docked to a patient interface device with an iris image of the same eye that is docked to the patient interface, to calculate a rotation angle between the two images. The astigmatism axis of the eye is measured when the eye is not docked, and the measured axis is rotated by the calculated rotation angle to obtain a rotated astigmatism axis relative to the iris image of the docked eye. The laser cataract procedure is performed based on the rotated astigmatism axis. The rotation angle is calculated by optimizing a transformation that transforms the undocked iris image to match the docked iris image, where the transformation includes a dilation factor that accounts for different pupil dilation of the two iris images.