A novel liquid lens optical component capable of focus and astigmatism correction: application to an innovative phoropter

Abstract

Purpose: Today the most reliable measurements for eyeglasses prescription rely on the use of a phoropter with an iterative positioning of a set of spherical and cylindrical lenses in front of the eyes. We present the design and the experimental evaluation of a novel compact, portable and low cost system for visual acuity measurement based on a single adaptive-optics component with continuously variable optical power, cylinder power and cylinder axis.

Methods: The adaptive-optics component, an 8mm optical aperture diameter liquid lens based on electrowetting, was designed using two encapsulated liquids with different refractive indexes, the interface of which is centered within a conical part. The shape of the liquid interface can be continuously controlled by bias voltages thanks to a multi-electrode design on the conical part, leading to a variable spherical and cylindrical diopter. The novel system for visual acuity measurement consists of two liquid lenses installed on a trial frame, with a driving electronics and a user command interface. The key performances of the system for visual acuity measurement were analyzed using a Shack-Hartmann optical wave-front analyzer. The system was also tested on a few patients to check its operational convenience.

Results: The lens with its driver provides a pure spherical power correction from -13D (Diopter) to +15D and a cylinder correction up to -6D with a spherical power included between -6D and +15D. Over this range, an optical power accuracy lower than 0.25D has been demonstrated. The cylinder axis can be controlled with an accuracy better than 3°. The maximal optical wave-front error is below 120nm-rms over a 4mm diameter pupil. And the focus control response time is lower than 300ms.

Conclusions: The optical performances evaluation has demonstrated the relevance of our system for visual acuity tests. The range of correction should be large enough to examine ametropia on 98% of the worldwide population and an additional fixed lens could be used to measure extreme optical corrections. Moreover the first tests on patients highlight the convenience of the system due to the absence of disruption in the test chart visualization when the optical settings are changed and to the possibility for the patient to tune the settings by himself.