Fluidic lenses have been developed for ophthalmic applications. The lenses use a pressure differential to deform a membrane, which separates two fluids with different indexes of refraction. The change in membrane shape creates changes in the optical wavefront. By utilizing different boundary conditions on the membrane, the progression of the membrane shape can be controlled. Specifically, a circular restraint is used to produce optical power, whereas a rectangular restraint is used to produce a combination of power and astigmatism. These lenses are analyzed for dominant properties and wavefront quality. By combining 2 rectangular restraint lenses at 45° and a circular restraint lens, both orthogonal second order Zernike astigmatisms as well as second order power can be independently controlled. This combination can also be described as independent control of ophthalmic cylinder, cylinder axis, and power, which is required to create a basic phoropter. A fluidic phoropter is demonstrated and analyzed in this manuscript.

Phoropters are the most common instrument used to detect refractive errors. During a refractive exam, lenses are flipped in front of the patient who looks at the eye chart and tries to read the symbols. The procedure is fully dependent on the cooperation of the patient to read the eye chart, provides only a subjective measurement of visual acuity, and can at best provide a rough estimate of the patient's vision. Phoropters are difficult to use for mass screenings requiring a skilled examiner, and it is hard to screen young children and the elderly etc. We have developed a simplified, lightweight automatic phoropter that can measure the optical error of the eye objectively without requiring the patient's input. The automatic holographic adaptive phoropter is based on a Shack-Hartmann wave front sensor and three computer-controlled fluidic lenses. The fluidic lens system is designed to be able to provide power and astigmatic corrections over a large range of corrections without the need for verbal feedback from the patient in less than 20 seconds.

A device for performing an objective eye exam has been developed to automatically determine ophthalmic prescriptions. The closed loop fluidic auto-phoropter has been designed, modeled, fabricated and tested for the automatic measurement and correction of a patient's prescriptions. The adaptive phoropter is designed through the combination of a spherical-powered fluidic lens and two cylindrical fluidic lenses that are orientated 45° relative to each other. In addition, the system incorporates Shack-Hartmann wavefront sensing technology to identify the eye's wavefront error and corresponding prescription. Using the wavefront error information, the fluidic auto-phoropter nulls the eye's lower order wavefront error by applying the appropriate volumes to the fluidic lenses. The combination of the Shack-Hartmann wavefront sensor the fluidic auto-phoropter allows for the identification and control of spherical refractive error, as well as cylinder error and axis; thus, creating a truly automated refractometer and corrective system. The fluidic auto-phoropter is capable of correcting defocus error ranging from −20D to 20D and astigmatism from −10D to 10D. The transmissive see-through design allows for the observation of natural scenes through the system at varying object planes with no additional imaging optics in the patient's line of sight. In this research, two generations of the fluidic auto-phoropter are designed and tested; the first generation uses traditional glass optics for the measurement channel. The second generation of the fluidic auto-phoropter takes advantage of the progress in the development of holographic optical elements (HOEs) to replace all the traditional glass optics. The addition of the HOEs has enabled the development of a more compact, inexpensive and easily reproducible system without compromising its performance. Additionally, the fluidic lenses were tested during a National Aeronautics Space Administration (NASA) parabolic flight campaign, to determine the effect of varying gravitational acceleration on the performance and image quality of the fluidic lenses. Wavefront analysis has indicated that flight turbulence and the varying levels of gravitational acceleration ranging from zero-G (microgravity) to 2G (hypergravity) had minimal effect on the performance of the fluidic lenses, except for small changes in defocus; making them suitable for potential use in a portable space-based fluidic auto-phoropter.

Thesis (M. A. (Optom.)) -- University of Limpopo, 2021 / Background: There are several clinical techniques for the subjective measurement of heterophoria. In South Africa, von Graefe is one of the most commonly used techniques to quantify heterophoria using the phoropter. However, most rural community clinics have trial frames rather than phoropters to perform heterophoria measurements and other clinical tests. Heterophoria or phoria is the misalignment of an eye that occurs when binocular sensory fusion is blocked. The distance heterophoria is determined by the tonic vergence resting state and negative accommodative vergence. In distance vision, normal heterophoria is zero. The tonic vergence resting state is the vergence angle dictated by tonic vergence innervation alone. However, during a near heterophoria test, the vergence angle observed involves multiple innervational factors. Blocking binocular fusion eliminates disparity vergence innervation. Because of the dual interaction, the loss of disparity vergence innervation initiates simultaneous changes of accommodation innervation. Purpose: The purpose of the study was to investigate the agreement of von Graefe heterophoria measurement using the phoropter and a trial frame. Setting: The study was conducted at an Optometry Clinic, University of Limpopo, South Africa. Methods: Distance and near horizontal and vertical heterophoria measurements were performed on 88 visually-normal university students using the phoropter and a trial frame. The 95% limits of agreement were compared using the exact Bland-Altman statistical test. To measure the horizontal heterophoria, 12 prism base-in was placed before the right eye and 6 prism base-up before the left eye. The prism in front of the right eye was reduced until the participant reported that the two images were vertically aligned. The vertical heterophoria was measured by reducing the prism in front of the left eye until the participant reported that the two images were horizontally aligned. Zero deviation was recorded as ortho or orthophoria. Results: For distance horizontal heterophoria, the Von Graefe values were 0.39±2.0 and 0.38±1.8Δ with the phoropter and trial frame, respectively. The mean near v horizontal heterophoria were 3.69±3.3 and 4.13±3.27Δ with the phoropter and trial frame. There were no significant differences between the mean heterophorias measured using the phoropter and the trial frame, p ˃ 0.05. For the vertical heterophorias at distance and near vision, the means were close to orthophoria. The mean differences and limits of agreement showed good agreement of Von Graefe test using the phoropter and trial frame. Conclusion: Measurement of Von Graefe testing with the phoropter and trial frame showed a high level of agreement for both distance and near vision performed through the phoropter and a trial frame. For clinical and research purposes, the phoropter and trial frame can be used interchangeably for measuring heterophoria. Keywords: heterophoria, phoropter, trial frame, von Graefe, prism

Adaptive optic technology has revolutionized real time correction of wavefront aberrations. Optofluidic based applied optic devices have offered an opportunity to produce flexible refractive lenses in the correction of wavefronts. Fluidic lenses have superiority relative to their solid lens counterparts in their capabilities of producing tunable optical systems, that when synchronized, can produce real time variable systems with no moving parts. We have developed optofluidic fluidic lenses for applications of applied optical devices, as well as ophthalmic optic devices. The first half of this dissertation discusses the production of fluidic lenses as optical devices. In addition, the design and testing of various fluidic systems made with these components are evaluated. We begin with the creation of spherical or defocus singlet fluidic lenses. We then produced zoom optical systems with no moving parts by synchronizing combinations of these fluidic spherical lenses. The variable power zoom system incorporates two singlet fluidic lenses that are synchronized. The coupled device has no moving parts and has produced a magnification range of 0.1 x to 10 x or a 20 x magnification range. The chapter after fluidic zoom technology focuses on producing achromatic lens designs. We offer an analysis of a hybrid diffractive and refractive achromat that offers discrete achromatized variable focal lengths. In addition, we offer a design of a fully optofluidic based achromatic lens. By synchronizing the two membrane surfaces of the fluidic achromat we develop a design for a fluidic achromatic lens.The second half of this dissertation discusses the production of optofluidic technology in ophthalmic applications. We begin with an introduction to an optofluidic phoropter system. A fluidic phoropter is designed through the combination of a defocus lens with two cylindrical fluidic lenses that are orientated 45° relative to each other. Here we discuss the designs of the fluidic cylindrical lens coupled with a previously discussed defocus singlet lens. We then couple this optofluidic phoropter with relay optics and Shack-Hartmann wavefront sensing technology to produce an auto-phoropter device. The auto-phoropter system combines a refractometer designed Shack-Hartmann wavefront sensor with the compact refractive fluidic lens phoropter. This combination allows for the identification and control of ophthalmic cylinder, cylinder axis, as well as refractive error. The closed loop system of the fluidic phoropter with refractometer enables for the creation of our see-through auto-phoropter system. The design and testing of several generations of transmissive see-through auto-phoropter devices are presented in this section.