Inspection of ophthalmic lenses using absorption

Abstract

A method and system for inspecting ophthalmic lenses using absorption where an ophthalmic lens is illuminated with light comprising wavelengths that are substantially absorptive to said lens, the image subsequently detected being created using only light at said absorptive wavelengths. Variations in transmitted light intensity translate into thickness changes in the lens caused by cosmetic flaws. The invention is also directed to imaging lens assemblies employing highly positive-powered field flattening lens elements to image a curved object, such as an ophthalmic lens, onto a flat image plane.

Description

[0001] 1. Field of the Invention[0002] The invention pertains to the inspection of optical media, such as ophthalmic lenses. More particularly, it relates to a method and system for inspecting ophthalmic lenses using light at wavelengths that are substantially absorptive to the ophthalmic lens, e.g. light at select ultraviolet (UV) or infrared (IR) wavelengths when the lens is a soft contact lenses. In an image of the lens generated therefrom, thickness changes caused by cosmetic flaws or thickness changes that are deliberately designed into the ophthalmic lens, manifest as measurable changes in transmitted light intensity. In practice, the invention reduces the number of false rejections by enabling a significant increase in the level of discrimination between cosmetic flaws critical to lens quality and extraneous artifacts which are not; and permits verification that intentional changes in lens thickness meet specification. The invention is especially adaptable to high speed, auto...

AI Technical Summary

Benefits of technology

This approach enhances the discrimination between critical cosmetic flaws and non-critical artifacts, reducing false rejections and enabling precise verification of intentional lens design features, while allowing for high-speed, automated inspection without removing lenses from molds.

Problems solved by technology

The labor intensive and subjective nature of human operator inspections impelled interest in automating aspects of the process.

Because white light is employed in these prior techniques, irrelevant lens detail is often imaged while important detail is lost.

This can result in too many false rejections of lenses.

Such a method is limited, however, by the types of materials that can be analyzed by fluorescence.

Furthermore, these earlier techniques are inadequate to measure deliberate changes in lens thickness, such as occurs with toric thin zones in certain types of contact lenses, to verify that they meet specification.

The difficulty with such configurations, however, is that the ophthalmic lens being imaged is oftentimes curved (e.g. to fit the eyeball in the case of a contact lens), not flat.

The result is a compromise in focus, to the diminishment of the inspection process.

These can be caused by cosmetic flaws, irregularities or can be due to the design of a particular ophthalmic lens.

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