Isao Minegishi

Axial eye-length measurement by wavelength-shift interferometry

A simplified noncontact measuring technique for axial eye length was developed. According to this method, the wavelength shift of a single-mode laser-diode beam that is irradiated onto the eyeball causes a phase shift in the interference fringes of reflections from the retina and the cornea. Then the optical distance between the cornea and the retina is obtained from the phase-shift measurement. High-speed axial eye-length measurements can be performed by using a laser diode on a pulse-modulation drive and signals from the reference light path as an analog-to-digital-conversion trigger. Compared with the technique that uses partially coherent light, this technique is inferior in terms of measurement accuracy but superior in its wide, measurable range of 16-32 mm. The results of measurements of 21 adults showed that 2 standard deviations of measurement was 2 sigma = +/- 0.11 mm.

Compensation of model eye's aberration by using deformable mirror

This paper reports on compensation for human eye aberration using a membrane deformable mirror(DM) which is fabricated by the MEMS process. The DM consists of a silicon(Si) membrane formed by processing of an SOI wafer and 85 electrodes. The diameter of Si membrane is 12mm and the maximum displacement is 16μm at a driving voltage of 180V. We have successfully demonstrated compensation for a model eyes aberration by using the DM. The model eyes aberration measured by the Shack-Hartmann wavefront sensor was expanded into Zernike polynomials and the driving voltages for the DM were decided so that the membrane shape would cancel out the eyes aberration by using appropriate voltage arrangements for each of the Zernike polynomials, these arrangements being predetermined experimentally. We have corrected the aberration of the model eye to less than 0.1μm-RMS. In this experiment, the effective diameter of the DM was 7.5mm, and the pupil of the model eye was 8.5mm.