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"1. Introduction

Degradation of vision is common in all human beings. The biological lens in our eyes starts to degrade creating refractive errors of vision by the age of 45. The four most common refractive errors of vision are myopia (nearsightedness); hyperopia (farsightedness), where far and nearby objects are seen out of focus, respectively; astigmatism, where vision is distorted by an irregularly curved cornea; and presbyopia which leads to loss of focal accommodation and difficulty in reading at arm's length [1–3]. Presbyopia is mostly an age related condition as the average accommodation range drops from 11 diopters on 20 year olds to 2 diopters by the age of 50 [4]. Worldwide in 2005, over one billion people were estimated to suffer from presbyopia alone [5].

Refractive errors cannot be prevented, but they are treated with corrective devices such as glasses, contact lenses, and refractive surgery. Eyeglasses correct refractive errors by shifting the focal plane by a fixed diopter amount, but often these tools do not provide satisfactory solutions. For example, many myopia and hyperopia sufferers often suffer from presbyopia as well; thus they may require several sets of eyeglasses with different mono-focal, bifocal, trifocal, and progressive lenses [6–9]. Eyeglasses cannot restore the accommodation range of a normal eye; hence these solutions partition the visible field onto smaller focal zones suitable to observe objects at different distances. Lens zoning greatly reduce the effective field of view; thus resulting in significant visual impairment.

The full field of view can be restored if the eyeglass lenses have a variable power that adaptively accommodates to the object distance. In order to address the need of most eyeglass corrected problems, the lens should have an accommodation range from −4 to + 4 diopters. Furthermore, the lenses should be light and thin with the aperture of 30-45 mm in diameter. The lens power should be adjusted at a minimum electrical power expense to ensure long battery operation. In this paper we present the implementation of an electrically actuated variable power lens with aperture and power range suitable for adaptive eyeglass applications."

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