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Shape change, not just motion, explains accommodative mechanism of crystalens
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CHICAGO — A previously undescribed “accommodative arching” theory helps to explain the accommodative mechanism of action of both the natural crystalline lens and the crystalens, one researcher said.
Kevin Waltz, OD, MD, described accommodative arching as a nonsymmetrical response when the eye accommodates, “resulting in a characteristic wavefront pattern and increase in higher-order aberrations.”
Dr. Waltz discussed this theory at a press breakfast hosted here by eyeonics.
“Accommodative arching is a phenomenon that we have observed in crystalens originally. We then looked back at natural human crystalline lenses to see if the same thing occurred in the normal state, and it does,” he said.
“This was to the best of my knowledge an unintended, incredibly beneficial observation with the design of the crystalens,” he said. “We think some of the unique structures of the crystalens contribute to this observed benefit.”
To validate the theory, Dr. Waltz used the iTrace by Tracey Technologies to measure phakic and aphakic patients focusing on targets at near and distance. Image data from the iTrace showed that the refraction and accommodation from near to distance is asymmetrical.
“After doing thousands of these tests, I have never once seen a symmetrical response,” he said.
One criticism of the crystalens, according to Dr. Waltz, has been that there is no way to show mathematically how it achieves 3 D to 5 D of accommodation, “yet we achieve this,” he said.
Dr. Waltz illustrated the accommodative arching phenomenon by describing a sphere, which has a set surface area. If one area of the sphere is flattened, a compensatory part of the sphere must also change, he said.
“It takes about 0.3 mm of forward motion to account for 10 D [of accommodation], but if you actually change the curvature, then you just need fractions of a millimeter of forward motion to account for diopters of accommodation,” he said. “We know now this can occur sometimes with the crystalens.”