Purpose:
Develop an advanced holographic binocular adaptive see-through phoropter that automatically measures spherical and cylindrical error and nulls this error with a compound sphero-cylindrical fluidic lens. The system is a compact wide field viewing design that automatically corrects for astigmatism and spherical refractive error.
Methods:
The compact system is comprised of three modules: a fluidic lens with any sphere, cylinder, and axis combination, a holographic relay telescope and a Shack-Hartmann sensor. This binocular system concurrently measures refractive error by: (1) Shining Infrared light that scatters off the retina. (2) The scattered light exits the eyes as an emerging wavefront that is relayed to the Shack-Hartmann sensor. (3) The sensor reconstructs the wavefront and extracts the sphero-cylindrical refractive error. (4) This prescription is applied to adjust the fluid volume, nulling out each eye's refractive error while the user views an eye chart. The users’ field of view is drastically enhanced with only the stack of fluidic lenses and beamsplitter on axis in the user’s line of sight. The beamsplitter also passes visible light, allowing for the subject to view external targets such as an eye chart. The beamsplitters additional modality is to direct infrared light toward the eye and reflect light back through the off-axis holographic telescopic system to the final module: a Shack-Hartmann wavefront sensor. The holographic telescope applies volume holograms operating at Bragg's Regime to drastically reduce the system size. Our holographic optical elements operate in the infrared and produce direct geometry optical lens replication. The adaptive phoropter prototype fits in a 60 mm long by 240 mm wide area.
Results:
Our prototype is capable of correcting a spherical refractive error from -10 to 10 D and astigmatic refractive error from -5 to 5 D. The Shack Hartmann sensor is capable of measuring spherical refractive error from -25 D 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. The range of the prototype may be increased to beyond the limits of the Shack-Hartmann sensor through further experimentation with system controls.
Conclusions:
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 refractive error. The goal is to produce a reliable binocular device that allows for quick and inexpensive objective measurements of a subject’s refractive error. Our advanced protytpe achieves this in a compact design while concurrently allowing a user a wide field of view.
Keywords: refractive error development • imaging/image analysis: non-clinical • optical properties