Computerized Moiré analysis of progressive addition lenses

Area of Science:

• Optics
• Image Analysis
• Ophthalmic Lens Metrology

Background:

• Accurate characterization of ophthalmic lenses is crucial for visual performance.
• Existing methods for analyzing lens power, especially progressive-addition lenses (PALs), can be complex or time-consuming.
• Digital image processing offers potential for novel metrology techniques.

Purpose of the Study:

• To develop and evaluate a novel, rapid, and repeatable method for analyzing ophthalmic lens power distribution.
• To investigate the utility of subtractive Moiré analysis for comparing magnification effects induced by lenses.
• To assess the variability between different brands of progressive-addition lenses (PALs).

Main Methods:

• A computerized image capture system with 256-level intensity resolution was employed.
• Digital images of a standard square-wave grating were acquired with and without an ophthalmic lens.
• Subtractive Moiré analysis was performed by digitally subtracting the pixel intensity distributions of the two images.

Main Results:

• The subtractive Moiré patterns graphically represented the power distribution of the tested ophthalmic lenses.
• Significant variations in Moiré patterns were observed between different brands of progressive-addition lenses (PALs) with the same nominal power.
• The method proved to be fast and repeatable using commercially available components.

Conclusions:

• Digital subtractive Moiré analysis provides a fast, repeatable, and graphical method for assessing ophthalmic lens power.
• The technique effectively highlights variations in magnification and power across different progressive-addition lens brands.
• This approach offers value to ophthalmic lens manufacturers and finishers for quality control and product development.