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P.A. Meyer; An Adjustable Focus Air Lens to Treat Presbyopia . Invest. Ophthalmol. Vis. Sci. 2005;46(13):698.
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Purpose: Spectacles currently used to treat presbyopia can offer a wide field of view only if they have a single focal plane. Those with multiple focal lengths have either discrete facets for infinity and the near point or distant and near corrections that are joined by a narrow corridor of increasing positive power. Optics that provide a wide field for any selected focal plane have been attempted by varying sphericity or refractive index, however such approaches suffer from mechanical or material complexity. Therefore, a lens has been developed that is composed of solid optical elements, has a wide field and adjustable focal length and is thin and light enough to be worn as spectacles. Methods: The hitherto undescribed optical system employs refraction at either side of an air cleft between the nesting parallel spherical surfaces of two optical elements. As they are separated, the resulting variable thickness air lens develops positive power which increases in proportion to the depth of the cleft. A light–weight mechanism that separates two lens pairs by identical distances, simultaneously, rapidly and accurately has also been developed and constructed. Results: The adjustable focus air lens proves to be particularly suitable for use in spectacles. A presbyopic subject can select at will any focal plane from infinity to the near point. Regardless of the chosen focal length, the optical properties are excellent, with minimal spherical aberration and high resolution over a very wide field. Projection of the principal plane close to the anterior segment of the eye maximises the available aperture and the orientation of the spherical surfaces ensures that there is very little astigmatism, regardless of angle of gaze. Conclusions: Using a novel optical system and actuating mechanism, it has become possible to treat presbyopia with glass or plastic spectacles that have adjustable focal length and high resolution at any chosen focal plane. The adjustable focus air lens is also likely to have wide applications outside ophthalmology.
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