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N Doble, G-Y Yoon, L Chen, B Singer, P Bierden, S Olivier, D Williams; Low Cost, Compact Wavefront Correctors for Ophthalmic Instrumentation Equipped with Adaptive Optics . Invest. Ophthalmol. Vis. Sci. 2002;43(13):955.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Current adaptive optics (AO) systems for the eye provide high spatial and temporal correction of ocular aberrations. However, such systems are large and expensive, primarily due to the deformable mirror (DM) (97 channels, 80mm diameter, ≷$100K ) used. Widespread use of AO in the eye for clinical and research applications requires the development of small, low cost wavefront correctors. We describe here the testing of two alternative DMs that satisfy these two requirements. Methods: We have modified the current Rochester AO system to test both a Boston Micromachines microelectromechanical (MEMS) mirror and a Hamamatsu liquid crystal spatial light modulator (LC-SLM). Both devices were characterized interferometrically and then incorporated into the AO system. They were controlled using a Hartmann-Shack wavefront sensor with a direct slope control algorithm. This method provides the best control both spatially and temporally. Results: Interferometric testing of the LC-SLM shows that its stroke is 0.8 microns. This is enough for wavefront correction of the eye provided phase wrapping is implemented and monochromatic, but not broadband light is used. The LC-SLM has better spatial resolution than any other wavefront corrector (480x480 pixels, 20x20mm). We have demonstrated the first closed loop AO system using the low cost, compact (3.3x3.3mm) MEMS mirror. Good correction of the eye's aberration was achieved for a 4.6mm pupil with compensation in 200msec. One subject had an initial rms wavefront aberration of 0.41±0.03mm giving a Strehl ratio of 6%. Upon AO correction the rms had dropped to 0.10±0.02mm with the Strehl increasing to 53±10%. Similar corrections were obtained for other subjects. This is in good agreement with the conventional 97 channel DM. Conclusion: For vision science, an ideal mirror should have a large stroke (≷10microns), good spatial resolution, and wavelength independence. Current MEMS devices have insufficient stroke for highly aberrated eyes but good resolution. LC-SLMs have excellent resolution but their use is confined to monochromatic light, which may be a good choice in a scanning laser ophthalmoscope. Both these devices offer better properties than micromachined membrane DMs that have lower spatial resolution and stroke.
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