Abstract
Purpose: :
Presbyopia is an age-related loss of accommodation of the human eye that manifests itself as inability to shift focus from distant to near objects. More than 90% of the people over 50 need correction of presbyopia. The conventional corrective lenses (bifocal, trifocal) have been around for more than 200 years and have some drawbacks. They have a limited field of view for each vision task, requiring user to gaze down to accomplish near vision and in some cases causing dizziness and discomfort. Some users need three different eyeglasses for reading, computer, and driving. Progressive lenses cause some distortion. An electro-optic lens allows voltage controlled change of the focusing power across the entire aperture and may provide a new approach to correction of presbyopia by eliminating the above limitations.Such a lens must have high light efficiency, relatively large aperture, fast switching time, low driving voltage, and power-failure-safe configuration. These requirements have not been met simultaneously in the past.
Methods: :
We demonstrate new switchable, flat, thin liquid crystal lenses that satisfy the above requirements. Various characterizations of the lens is performed, including diffraction efficiency as a function of the lens diameter and lens location, response time, wavefront, higher-order aberration, modulation transfer function, off-axis imaging property, and chromatic aberration.A polarizing microscope is used to check the response of liquid crystal to the electrical field in a local area, and a computer interfaced, phase-shifting Mach-Zehnder interferometer is used to measure the wavefront. A setup with a multi-wavelength laser has been build to characterize the transverse chromatic aberration.
Results: :
Lenses with switchable powers between plano, 1(2)-diopter, and 2(4)-diopter have been fabricated. The lenses show high optical performance, including high diffraction efficiency (>91%), fast response time (<130ms), good spherical wavefront, small higher-order aberration, good modulation transfer function. The peak-to-valley range of the higher-order aberration is 0.241 and the RMS value is 0.039, which is comparable to a high quality reading glass., The effects of the gaps between the ring electrodes and the fringing field on the lens performance have been analyzed. The lens provides focusing powers and high optical performance for near-, intermediate-, and distance vision. Lenses with tunable power are being investigated.
Conclusions: :
This kind of lens is promising to become an alternative of conventional area division multi-focal spectacle lenses used by presbyopes. The new eyeglass will significantly improve the quality of life for a large population.
Keywords: presbyopia • spectacle lens • accomodation