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Demonstrates how gradient in sagittal power creates unwanted astigmatism in lenses, suggesting a need for design improvements.
A concentric variation in sagittal power, F s , with zonal radius, y, has been used in some designs of varifocal and aphakic spectacle lenses. It is shown theoretically, using a paraxial approximation, that a gradient dF s /dy in sagittal power leads to the introduction of an amount ydF s /dy of unwanted astigmatism. The validity of this result is illustrated experimentally.
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W. N. Charman (1982) studied this question.
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