Abstract
Using a phoropter to measure the refractive error is one of the most commonly used methods by ophthalmologists and optometrists. Here, we demonstrate design and fabrication of a portable automatic phoropter with no need for patient’s feedback. The system is based on three tunable-focus fluidic lenses and thin-film holographic optical elements to perform automatic refractive error measurement and provide a diagnostic prescription without supervision. Three separate lenses are deployed to correct the defocus and astigmatism. The refractive error is measured using a Shack-Hartmann wavefront sensor that calculates the Zernike values of an infrared wavefront emerging from the eye. Holographic optical elements steer the emerging wavefront into the wavefront sensor, while simultaneously providing an unobstructed view for the subject. The power of each lens is controlled by pumping a liquid in and out of the lens chamber using servo motor actuated diaphragm pumps. Spherical and cylindrical correction range of −10 to +10 diopters with 0.1 diopter increments is achieved in less than 15 seconds using wavefront sensor feedback to the pumps. This system can be used in rapid screening of large patient populations especially in the developing countries that lack sufficient facilities and specialist doctors.
Highlights
Refractive Error (RE) is among the main concerns of public health, with uncorrected RE being the leading cause[1] of visual impairment
The power reaching the eye from the laser is ~0.6 mW/cm[2], which is less than Maximum Permissible Exposure (MPE) at the cornea[37] (1 mW/cm2)
After reflecting back from the retina and going through the tunable lenses, the IR light is redirected by two holographic optical elements (HOEs) into the Shack-Hartmann wavefront sensors
Summary
Refractive Error (RE) is among the main concerns of public health, with uncorrected RE being the leading cause[1] of visual impairment. Various methods have been investigated to fabricate and control liquid lenses[19,20,21,22,23,24,25] of which externally actuated hydraulic pumps have shown good control and large variations in focal lengths[26,27] Most of these methods are limited to spherical powers, recent studies have shown tunable astigmatism in liquid lenses[28,29] as well. One main advantage of HOEs is their ability to work in specific wavelength while being transparent to other wavelengths, which enables them to project the pupil onto the wavefront detector without blocking the patient’s view This would enable subjective verification of the prescribed data using fluidic lenses. We present the design of HOEs so that they redirect the infrared (IR) light while being transparent in visible wavelength in order to keep an unobstructed view for the patient
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