ADAPTIVE OPTICS

An advanced “see-through†automated adaptive optics phoropter could greatly simplify patient refraction, reducing the need for highly trained personnel and increasing office efficiency, Gholam A Peyman MD told the Innovators Session of the ASCRS annual symposium. The new phoropter eliminates the need to flip lenses, making it possible to operate the unit automatically or for the patient to manually adjust it. Not only is it objective, easier and quicker to use, it also refracts to within 0.1 D compared with . D steps in manual phoropters, Dr Peyman said. “Our objective was to develop an automated see-through adaptive optics phoropter for correction of refractive errors while the patient is looking at far or near.â€

Three lenses, no moving parts

The binocular system developed at the University of Arizona, Tucson, US, in collaboration with Drs Savidis, Schweugerling and Peyghambarian, uses computer-controlled adaptive fluidic lenses coupled with a refractive or holographic relay telescope and a see-through Shack- Hartmann sensor, allowing refraction of both eyes simultaneously, Dr Peyman said. It replaces the multiple glass lenses of traditional phoropters with three fluidic lenses; one spherical and two cylindrical. The lenses are composed of a deformable silicone membrane and a lens fluid chamber. Increasing or decreasing the fluid in the spherical changes power from -20.0 to +20.00 D in 0.1 D steps. Cylinder lenses power ranges from 0.0 to 8.0 in 0.1 D steps. Combining the two lenses at a 45-degree orientation creates a universal astigmatic lens capable of creating a universal cylinder at any axis. This eliminates the need to move any lens in the system. Instead, the lens power is controlled by a computer, which determines how much fluid is pumped into each of the three lenses in a closed loop interaction. Incoming light is reflected into the eye and then back into the telescopic or holographic refractive system, which adjusts for sphere and astigmatism using the Shack-Hartmann sensor.

Thinner

To make the system thinner and lighter, Dr Peyman and associates incorporated an array of diffractive liquid crystal lenses and a holographic optical element to replace the standard telescope, and a diffractive-refractive achromatic lens to replace the spherical lens. The diffractive optic breaks up incoming light into numerous waves and then recombines them into new waves. Electrical charges on liquid crystal differentially arrange the crystals to produce a new spherical wave. To control for chromatic aberration, they combined a refractive fluidic lens with a diffractive liquid crystal lens to cancel each other’s chromatic aberrations. The holographic optical element creates a 3-D virtual image, which enables the system to simulate depth. It is monochromatic, which is a disadvantage, but it also has several advantages, Dr Peyman noted. A single holographic element can create a wavefront of any shape, and it is virtually distortion-free, focusing to the diffraction limit with submicron accuracy. It also allows close to 100 per cent diffraction efficiency with minimal light absorption. It has large apertures, allowing wide field of view. It is lightweight, easily replicated and inexpensive. The third-generation binocular system allows practical, rapid vision tests in both eyes simultaneously, Dr Peyman said. Dr Peyman owns a patent and shares two pending applications with his colleagues from the university of Arizona.