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N. Savidis, R. Marks, N. Peyghambarian, D. Mathine, G. Peyman, J. Schwiegerling; Developing an Adaptive Phoropter Through the Application of a Fluidic Lens and Shack Hartmann Sensor. Invest. Ophthalmol. Vis. Sci. 2010;51(13):3946.
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Develop an adaptive phoropter that automatically measures spherical and cylindrical error and nulls this error with a sphero-cylindrical fluidic lens.
An automated phoropter has been designed and fabricated. The system is comprised of three modules: a fluidic lens, a relay telescope and a Shack-Hartmann sensor. The fluidic lens is a stack of three adjustable lenses composed of a spherical lens and two astigmatic lenses oriented 45 degrees to one another. Any sphere, cylinder and axis combination can be achieved by adjusting the fluid volume within the fluidic lenses. Following the fluidic lens, are a relay telescope and a beamsplitter. The beamsplitter directs infrared light towards the final module: a Shack-Hartmann wavefront sensor. The beamsplitter also passes visible light, allowing for the subject to view external targets such as an eye chart. The system works as follows. (1) Infrared light is shone into the eye and scatters from the retina. (2) The scattered light exits the eye as an emerging wavefront that is relayed through the fluidic lens to the Shack-Hartmann sensor. The sensor reconstructs the wavefront and extracts the sphero-cylindrical refractive error. This prescription is then applied to adjust the volume of the fluidic lenses in an attempt to null out the refractive error. Feedback of the wavefront from the eye/fluidic lens combination is then used to monitor the fluid volume and keep the net refractive error at a minimum. A raytracing model has been developed to determine the properties and ranges of the automated phoropter.
The raytracing model shows that the Shack Hartmann sensor is capable of measuring a spherical refractive error from -25 to 40 D. Even in cases of extreme myopia or hyperopia, a limited number of spots are needed to drive the fluidic lens power in an appropriate direction, forcing the Shack-Hartmann pattern into a more useable range.
Fluidic lenses coupled with a Shack-Hartmann sensor applied in an eye examination have the potential of creating an automated means of measuring and nulling a subject’s prescription. The goal is to produce a reliable device that allows for quick and inexpensive objective measurement of a subject’s prescription.
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