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E. Acosta, S. Chamadoira, R. Blendowske; Interferometric Lens Meter for the Testing of Local Second and Higher Order Aberrations of Progressive Addition Lenses. Invest. Ophthalmol. Vis. Sci. 2010;51(13):3945.
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To develop a simple experimental set-up to determine the local aberrations of progressive addition lenses. Aberration variation resulting from increased patch size around the measurement is also included. In the case of small patches, where higher order aberrations are negligible, the set-up provides the local dioptric power matrix (sphere and astigmatism) of the lens.
The experimental set-up is basically a point diffraction interferometer which has been modified in order to provide fringe patterns within small areas of the lens (patch diameters ranging from 1 to 5 mm). The lens remains in a fixed position and only one part of the set-up needs to be translated along one axis (approximately 20 mm), acting like a Badal system to compensate for defocus, and on the perpendicular plane (approximately 3 mm) to compensate for prismatic effects. Additionally, the region under test is selected in accordance with this movement.
The calibration of the most simple version of the set-up shows that local sphere and astigmatism are determined with less than 0.1 D accuracy. Higher order aberrations are determined with an accuracy of about one tenth of a wavelength. In this first version, the inspection area is within a circle measuring approximately 25 mm in diameter. No compensating optics are used to correct the sphere and no rotatable elements or compensating prisms are used to choose the region of interest or to scan the lens. Range of measurement is -10 D to 10 D for additions up to 2.5 D. And lastly, it is worth pointing out that the number of measurement zones can be selected based on user criteria (from a single zone up to a complete scan in increments of 1 mm in both directions). In any case, the diameter of the region of interest around the point can also be chosen.
We have developed a compact and robust interferometric lens meter capable of providing both the map of local sphere and astigmatism as well as aberrations for different pupil sizes. This will help to predict quality of vision through the different zones of progressive addition lenses.
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