Active image stabilization for an adaptive optics scanning laser ophthalmoscope (AOSLO) was developed and tested in
human subjects. The tracking device, a high speed, closed-loop optical servo which uses retinal features as tracking target, is separate from AOSLO optical path. The tracking system and AOSLO beams are combined via a dichroic beam
splitter in front of the eye. The primary tracking system galvanometer mirrors follow the motion of the eye. The AOSLO raster is stabilized by a secondary set of galvanometer mirrors in the AOSLO optical train which are "slaved"
to the primary mirrors with fixed scaling factors to match the angular gains of the optical systems. The AO system (at
830 nm) uses a MEMS-based deformable mirror (Boston Micromachines Inc.) for wave-front correction. The third
generation retinal tracking system achieves a bandwidth of greater than 1 kHz allowing acquisition of stabilized AO
images with an accuracy of <10 μm. However, such high tracking bandwidth, required for tracking saccades, results in
finite tracking position noise which is evident in AOSLO images. By means of filtering algorithms, the AOSLO raster is
made to follow the eye accurately with reduced tracking noise artifacts. The system design includes simultaneous presentation of non-AO, wide-field (~40 deg) live reference image captured with a line scanning laser ophthalmoscope
(LSLO) typically operating from 900 to 940nm. High-magnification (1-2 deg) AOSLO retinal scans easily positioned
on the retina in a drag-and-drop manner. Normal adult human volunteers were tested to optimize the tracking
instrumentation and to characterize AOSLO imaging performance. Automatic blink detection and tracking re-lock,
enabling reacquisition without operator intervention, were also tested. The tracking-enhanced AOSLO may become a
useful tool for eye research and for early detection and treatment of retinal diseases.