Wavefront-sensorless AO system dynamically images the human retina
The use of adaptive optics (AO) for imaging the retina of living human eyes has flourished.
The use of adaptive optics (AO) for imaging the retina of living human eyes has flourished. But the conventional AO setup, which uses a dynamic wavefront sensor in a closed feedback loop with a deformable mirror, has disadvantages for retinal imaging: The wavefront-sensor beacon is sometimes bright enough to interfere with examinations; the resolution limit of the wavefront sensor itself can limit system resolution; and an undilated pupil (for example, 3 mm in diameter) can even prevent the use of a wavefront sensor. To avoid these problems, a group at the University of Houston (Houston, TX) has created a wavefront-sensorless AO system that uses a stochastic parallel-gradient-descent algorithm to image a retina in real time (25 Hz).
In the dual-deformable-mirror scanning imaging system, a “woofer” and “tweeter” corrected low- and high-order aberrations, respectively. The parameter to be optimized was the reflected light from the retina that passed through a confocal pinhole averaged over the 1.5º field of view during the 35 ms frame-exposure time. Prior to gathering image data, a Shack-Hartmann wavefront sensor was used to check and correct for lower-order aberrations (mostly defocus) and was held static during the “sensorless” dynamic operation. Because the technique automatically focused on the most reflective retinal layer, a rapid alternating defocus may be needed to image other layers. Contact Heidi Hofer at email@example.com.