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J.F. Bille, M. Agopov, C. Alvarez, N. Korablinova, O. La Schiazza, F. Mueller, H. Zhang; Compact Adaptive Optics System for Multiphoton Fundus Imaging . Invest. Ophthalmol. Vis. Sci. 2006;47(13):4068.
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© ARVO (1962-2015); The Authors (2016-present)
A combination of adaptive optics techniques with multiphoton retinal imaging using femtosecond laser excitation is experimentally verified to improve the quality of retinal imaging.
The adaptive optics system was integrated into the system for multiphoton laser scanning ophthalmoscopy. Defocus, astigmatism, trefoil, and coma are compensated via a combination of telescope and rotating pairs of phase plates. The spherical aberration as well as all dynamic aberrations are corrected by an active micro–electro–mechanical (MEMS)–mirror. Confocal imaging and wavefront measurement are conducted with a red laser diode (lambda=675nm). The wavefront of the Ti:Sapphire femtosecond laser (lambda=750–925nm, tau=120fs, P up to 80mW, repetition rate 160MHz) is pre–modulated to compensate for the aberrations of the eye.
The adaptive optics systems was validated in a study on 60 eyes of 30 subjects. For description of optical quality, Strehl ratio was calculated from wavefront data. In all eyes, Strehl ratio for 5.5mm dark adapted pupils was below 0.05 without adaptive optics compensation. With static compensation, Strehl ratios of better than 0.40 were measured. In all eyes, diffraction limited performance (Strehl ratio better 0.80) could be achieved with full dynamic compensation in closed loop operation. The mean data with regard to root mean square wavefront error (RMS) improvements were as follows: RMS(total): 0.3µm to 0.14µm, RMS(2nd order): 0.2µm to 0.08µm, RMS(3rd order): 0.15µm to 0.065µm, RMS(4th order): 0.12µm to 0.05µm, RMS(5th order): 0.04µm to 0.04µm, RMS(6th order): 0.04µm to 0.04µm. The contributions of 5th and 6th order RMS errors were below the diffraction limit (lambda/14) as well as the resolution limit of the wavefront measurement technique. Experiments with a model–eye simulating the study–parameters on two–photon–excitation fluorescence (TPEF) on rat–eyes have shown that the compensation of the optical aberrations leads to micrometer resolution. The macular region could be visualized with greatly enhanced resolution and contrast with regard to TPEF–imaging in comparison to images without the use of adaptive optics.
The compact adaptive optics system can greatly improve the resolution and contrast of (TPEF)–fundus images. In this way, the study of physiological and biological processes of the retina can benefit from aberration free retinal imaging.
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