Handheld polarizing filter augments corneal imaging with simple approach
Use of a handheld circular polarizing filter to intercept afferent and efferent light from a slit lamp or operating microscope highlights corneal structures that are otherwise invisible or barely seen.
Circular polarization is a simple and effective technique for corneal imaging that provides valuable clinical information and new insights, according to Julian D. Stevens, MD.
“Ophthalmologists are all familiar with the benefits of cross polarization for improving imaging at the slit lamp, but conventionally, that would require an instrument with a built-in linear polarizer and use of another handheld polarizer,” said Dr. Stevens, consultant ophthalmic surgeon, Moorfields Eye Hospital, London.
“Use of a handheld circular polarizing filter gives the desired effect in a much simpler approach which can be used in by any practitioner, and I highly recommend it to corneal and refractive surgeons,” Dr. Stevens said.
Features within the cornea that are otherwise hidden are rendered visible, and the imaging technique highlights stress and biomechanical effects within the cornea, he noted.
“Through the ability to see these changes, we are better able to measure and understand them,” he said.
Fundamental principle
The photoelastic effect or stress birefringence was first described in 1816 by Scottish physicist, Sir David Brewster, according to Dr. Stevens.
“Brewster noted that optically isotropic or anisotropic transparent substances become birefringent when subjected to mechanical stress,” he said. “Cross polarization takes advantage of the strong polarizing effect of the cornea that arises from the arrangement of the collagen fibrils throughout its different layers.”
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