The adaptive optics scanning laser ophthalmoscope may be used in multi-wavelength mode to allow simultaneous
imaging and retinal stimulation and so probe retinal function. The wavelengths available are 532 nm, 658 nm and 840
nm. Typically the imaging is performed at 840 nm and precisely coincident retinal stimulation occurs in one of the
visible wavelengths. Simultaneous multi-wavelength imaging in the living human retina is demonstrated, and
experiments to test retinal function that may be carried out using this instrument are presented.
We present a clinically deployable adaptive optics scanning laser ophthalmoscope (AOSLO) that features
micro-electro-mechanical (MEMS) deformable mirror (DM) based adaptive optics (AO) and low coherent light sources.
With the miniaturized optical aperture of a μDMS-Multi<sup>TM</sup> MEMS DM (Boston Micromachines Corporation,
Watertown, MA), we were able to develop a compact and robust AOSLO optical system that occupies a 50 cm X 50 cm
area on a mobile optical table. We introduced low coherent light sources, which are superluminescent laser diodes
(SLD) at 680 nm with 9 nm bandwidth and 840 nm with 50 nm bandwidth, in confocal scanning ophthalmoscopy to
eliminate interference artifacts in the images. We selected a photo multiplier tube (PMT) for photon signal detection and
designed low noise video signal conditioning circuits. We employed an acoustic-optical (AOM) spatial light modulator
to modulate the light beam so that we could avoid unnecessary exposure to the retina or project a specific stimulus
pattern onto the retina. The MEMS DM based AO system demonstrated robust performance. The use of low coherent
light sources effectively mitigated the interference artifacts in the images and yielded high-fidelity retinal images of
contiguous cone mosaic. We imaged patients with inherited retinal degenerations including cone-rod dystrophy (CRD)
and retinitis pigmentosa (RP). We have produced high-fidelity, real-time, microscopic views of the living human retina
for healthy and diseased eyes.
A MEMS deformable mirror (DM)-based new generation adaptive optics scanning laser ophthalmoscope (AOSLO) has been developed for in-vivo microscopic imaging of the living human retina. With the miniaturized optical aperture of a μDMS-Multi<sup>TM</sup> MEMS DM made by Boston Micromachines Corporation (Watertown, MA), we were able to confine a compact and robust optical system to a mobile 30"×30" breadboard while keeping the system aberrations diffraction-limited over an imaging field of view up to 3×3 degrees. A customized Shack-Hartmann wavefront sensor was devised to facilitate the MEMS DM based adaptive optics (AO) system. The ocular aberration is compensated over a 6mm pupil based upon a modal wavefront correction strategy. The AO correction is done for both ingoing and outgoing paths of the scanning laser ophthalmoscope. After AO correction, the root mean square wave aberration is reduced to less than 0.1μm for most eyes. The lateral resolution is effectively enhanced and the images reveal clear cone mosaic near the foveal center. The significant increase of the throughput at the confocal pinhole allows for a confocal pinhole whose diameter is less than the Airy disc of the collection lens, thereby fully exploiting the axial resolution capabilities of the system. The MEMS DM as well as its successful application represents the most significant technological breakthrough of this new generation AOSLO.
A MEMS deformable mirror has recently been employed in the AO system of an adaptive optics scanning laser ophthalmoscope (AOSLO). MEMS allows for a more compact, efficient and effective system. The AO system in the AOSLO operates with a modal closed loop. Aberrations after AO reduce the wave aberration to less than 0.1 microns RMS in most eyes. Results show improved resolution, brightness and contrast. Images of patches of retina show a well resolved cone photoreceptor mosaic as they change in size with eccentricities ranging from 0.6 degrees to 4.23 degrees from the fovea.
We present a statistical assessment of the lateral resolution of the adaptive optics scanning laser ophthalmoscope (AOSLO). We adopt a 2-D Gaussian function to approximate the AOSLO point spread function (PSF), which is dominated by the residual wavefront aberration and characterized by the Strehl ratio. Thus, we derive the lateral resolution in the presence of residual wave aberrations, which is inversely proportional to square root of the Strehl ratio. The modeling, while not sufficient in describing the fine structure of the real PSF, demonstrates good conformance to the lateral cross section of the real PSF. With this model, the lateral resolution of our current AOSLO was computed to be 1.65 to 2.33 µm, which agreed well with the actual result. We also reveal the relationships among the lateral resolution and other three measures of the AOSLO imaging property including the Strehl ratio, the PSF, and the root mean square (rms) of wavefront aberration.