Iris Registration for Astigmatism Correction in Cataract Surgery
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Solution Overview
Problem
Existing methods for treating astigmatism during cataract surgery face challenges due to cyclotorsion of the eyes when transitioning from an upright to a supine position, leading to inaccuracies in aligning corneal curvature corrections or toric intraocular lens orientations.
Innovation Solution
An iris registration method that minimizes the Hamming distance in sequences of relatively shifted rubber sheet representations of iris images taken in both upright and supine positions, allowing for accurate computation of cyclotorsion rotation angles and alignment of astigmatism corrections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional iris registration algorithms are used to compute cyclotorsion rotation angle, then measurement precision is improved, but device complexity and computational cost increase
Solution Approach 1:
The iris image is segmented into multiple horizontal lines, and each line is independently processed through band-pass filtering and binarization. This segmentation allows the complex image registration problem to be broken down into simpler one-dimensional line comparisons, reducing overall computational complexity while maintaining precision.
Solution Approach 2:
The patent replaces complex conventional iris registration algorithms with a simplified computational approach based on Hamming distance calculation between binary representations of horizontal lines. This substitution uses basic digital signal processing operations instead of complex pattern recognition algorithms, significantly reducing computational burden.
2Manufacturing precision
If iris registration is performed to account for cyclotorsion, then manufacturing precision of astigmatism correction is improved, but loss of time increases
Solution Approach 1:
Instead of performing complete two-dimensional image registration, the patent applies partial action by only processing horizontal lines through band-pass filtering and binarization. This partial processing approach is sufficient to capture the essential cyclotorsion information while dramatically reducing processing time compared to full image registration.
Solution Approach 2:
The patent skips intermediate complex processing steps by directly computing the Hamming distance between binary horizontal lines to determine rotation angle. This rushing through of the registration process using simplified metrics achieves the necessary precision for astigmatism correction without the time cost of conventional algorithms.
Data Source
AI summary
A method implemented in an ophthalmic laser system to perform iris registration based on two iris images taken with the patient at upright and supine positions, respectively. For each iris image, the iris region is transformed into a rectangular rubbersheet, with the radial and angular coordinates of the iris image respectively mapped to vertical and horizontal coordinates of the rubbersheet. A horizontal one-dimensional log-Gabor transform is applied to the rubbersheet line-by-line. The transformed rubbersheet is binarized line-by-line. The two binary rubbersheets are compared at a series of relative horizontal shifts to determine the horizontal shift value that produces the lowest Hamming distance between the two binary rubbersheets, and the cyclotorsion rotation of the eye between the upright and supine positions is calculated accordingly. Then, while the patient is in the supine position, the laser system treats the eye based on measured astigmatism axis orientation and the calculated cyclotorsion rotation.