Novel refractive system offers many benefits

April 6, 2009

San Francisco-A new system combining a modified Shack Hartmann wavefront sensor with a new streamlined phoropter makes measurement of refractive error simpler, more efficient, and more accurate, said Gholam A. Peyman, MD.

San Francisco-A new system combining a modified Shack Hartmann wavefront sensor with a new streamlined phoropter makes measurement of refractive error simpler, more efficient, and more accurate, said Gholam A. Peyman, MD.

Dr. Peyman, clinical professor of ophthalmology, University of Arizona College of Medicine, Tucson, characterized the phoropter as “the heart of the system.” It replaces the lenses of a conventional phoropter with three fluidic (deformable) lenses-two cylindrical lenses and one spherical lens. The lenses allow for refinement of spherocylindrical error in steps of 0.1 D via remote control by a computer or the patient. The spherical lens power can be adjusted over the range of ± 20 D and the cylindrical power can vary from 0 to ± 8 D.

The lenses feature a deformable silicone membrane and a fluid chamber. Volumetric changes in the fluid chamber can be precisely controlled and result in a change in the silicone membrane curvature in either a concave or convex direction. Optical power of the lens is calculated based on the surface curvature and the indices of refraction of the silicone membrane and deionized water in the chamber. Variation of the optical wavefront also is achieved by computer-controlled injection or removal of fluid.

The integrated system automatically sets the starting point of the subjective refraction.Laboratory evaluation was performed in a model eye in which the fluidic lens system was able to correct refractive errors introduced in the model.

“Current phoropter systems have several limitations,” Dr. Peyman said. “Lenses are adjusted in steps of 0.25 D for both sphere and cylinder power, higher-order aberrations are not assessed or corrected, and the flipping of lenses is time-consuming.

“This new system reduces the need for skilled personnel and reduces chair time to increase office efficiency,” he concluded. “It is very patient friendly, and we believe it can provide more precise measurement than current refractive systems.”