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J. F. Bille, M. Agopov, R. Dong, N. Korablinova, O. La Schiazza, S. Sindbert, H. Zhang, F. Mueller; Hybrid Adaptive-Optical System for Aberration-Compensated Multiphoton Imaging of the Retina of the Human Eye. Invest. Ophthalmol. Vis. Sci. 2007;48(13):4266.
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Aberration-free retinal imaging can be achieved by compensation of the optical aberrations of the eye through adaptive optics. A combination of adaptive optics techniques with multiphoton retinal imaging using femtosecond laser excitation and a hybrid adaptive optical system comprising of a coherent gated wavefront sensor (CGWS), a phase-plate-based precompensator and a MEMS-mirror is experimentally verified.
The adaptive optical multiphoton ophthalmoscope consists of a precompensator, comprising of rotating pairs of phase-plates (defocus, astigmatisms, coma, trefoil), an active micro-electro-mechanical (MEMS)-mirror and a coherent gated wavefront sensor, comprising of an OCT-sensor, a phase-shifting interferometer (PSI) and a virtual Shack-Hartmann-Sensor (vSHS). The wavefront of the Ti:Sapphire femtosecond laser (=750-925nm, τ=120fs, Power up to 80mW, repetition rate 76MHz) is pre-modulated to compensate for the aberrations of the eye.
The resolution of the multiphoton ophthalmoscope can be substantially improved by using adaptive optics, i.e wavefront correction based on coherent gated wavefront sensing (CGWS). The advantage of using CGWS relies on the fact that the wavefront distortions are sensed by back-scattered light of the femtosecond laser source instead of fluorescent light. Thus, neither photodamage nor photoblaching occurs and wavefront distortions can be measured up to several scattering lengths deep within the retina. The experimental system allows for greatly improved contrast of two-photon excited fluorescence (TPEF)-imaging of the retinal pigment epithelial (RPE)-cell layer.
A combination of adaptive optics techniques with multiphoton retinal imaging using femtosecond laser excitation is experimentally verified to improve the contrast of TPEF-imaging of the RPE-cell layer. For the first time, a new wavefront sensing method: "coherent gated wavefront sensing (CGWS)" was applied for retinal imaging, allowing for adaptive-optical improvement of deep-laying retinal structures.
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