Micro-CT Scanning for Contact Lens Geometry Measurement
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Solution Overview
Problem
Current methods for measuring the geometry of ophthalmic lenses and molds are non-contact and non-destructive, but they are often inaccurate, slow, and cannot capture the entire geometry of complex surfaces like the base curve of contact lenses, due to limitations in scanner technologies and the need for direct line of sight, which also fails to account for volumetric shrinkage and hydration effects.
Innovation Solution
The use of micro computed tomography (microCT) to scan ophthalmic samples, including contact lenses, molds, and optical tools, with a rotatable platform to capture 3D geometry from multiple orientations, applying sub-pixel edge detection algorithms and archiving the data for iterative mold and process modifications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If current scanner technologies (vision, laser, interferometer, touch probe) are used to measure lens geometry, then measurement can be performed, but the measurement is inaccurate and cannot capture entire complex surfaces like base curve due to direct line of sight requirements
Solution Approach 1:
The patent transitions from 2D surface scanning (requiring direct line of sight) to 3D volumetric imaging using micro-CT. By acquiring X-ray projections from multiple angles and reconstructing the internal 3D geometry, the system can measure obscured surfaces like the base curve without direct optical access, as the X-rays penetrate through the lens material from all directions during rotation.
Solution Approach 2:
The patent replaces mechanical contact probing (touch probe) and optical line-of-sight scanning with non-contact X-ray tomography. The X-ray based micro-CT system eliminates the need for physical contact that deforms the lens and removes the geometric constraints of optical line-of-sight requirements, enabling measurement of previously inaccessible surfaces.
2Measurement precision
If the lens is supported by an optical tool for measurement, then the lens can be held stable, but the optical tool distorts the lens and results in inaccurate measurement of true lens geometry
Solution Approach 1:
The patent replaces mechanical/optical support systems with X-ray based volumetric imaging. Since micro-CT uses penetrating X-rays rather than physical contact or optical lines of sight, no external support structure is needed during measurement. The lens can be suspended or held in a minimal fixture, eliminating distortion from support tools while maintaining measurement stability through multi-angle projection acquisition.
3Measurement precision
If conventional scanning techniques are used, then measurement can be performed, but the lens must be precisely positioned within the scanner or accuracy is adversely affected
Solution Approach 1:
The patent acquires data in 3D space through rotation rather than requiring precise 2D positioning. By rotating the lens and acquiring X-ray projections from multiple angles, the system inherently captures the complete 3D geometry regardless of the lens's initial position on the rotation axis. The reconstruction algorithm automatically accounts for the rotational trajectory, eliminating the need for meticulous positioning that conventional scanners require.
Solution Approach 2:
The patent transforms a static positioning problem into a dynamic measurement process. Instead of requiring the lens to be perfectly positioned and held stationary, the system rotates the lens through a known angular trajectory while acquiring projections. This dynamic approach with controlled rotation makes the measurement robust to initial positioning variations, as the complete rotational path provides redundant information for accurate 3D reconstruction.
4Measurement precision
If micro computed tomography is used to scan ophthalmic samples, then high-resolution accurate measurements of complex 3D geometries including obscured surfaces can be obtained, but the device complexity increases
Solution Approach 1:
The patent employs a micro-CT system that serves multiple functions: it measures the lens geometry, characterizes the mold cavity geometry, detects internal defects, and provides 3D volumetric data for both the lens and mold. This multi-functional capability justifies the device complexity, as a single micro-CT system replaces what would otherwise require multiple specialized measurement instruments for different aspects of lens and mold characterization.
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
This approach provides high-resolution, accurate measurements of complex 3D geometries, including obscured surfaces, allowing for precise characterization of lens and mold geometries, and enabling feedback for improved manufacturing processes and quality control.
Implementation Method 1
providing a source of electromagnetic radiation at an intensity, providing a detector to detect the electromagnetic radiation intensity, positioning the sample such that the electromagnetic radiation generated by the source passes through the sample and to the detector, detecting the electromagnetic radiation intensity after passing through the sample
Implementation Method 2
The present system uses micro computed tomography to measure the geometries... providing a source of electromagnetic radiation... positioning the sample... detecting the electromagnetic radiation intensity... processing the electromagnetic radiation intensity detected to obtain a 2-dimensional image of the sample
Data Source
AI summary
The invention relates to an apparatus and method for non-contact/non-destructive measurement of the geometry of molded ophthalmic lenses and the precision molds and tooling used in the manufacture of the ophthalmic lenses. In particular the present system uses micro computed tomography to measure the geometries.