SFB Tomography across the scales: Adaptive optics in ophthalmic imaging

by Günter Auzinger, JKU Linz

Ophthalmoscopes are medical devices for non-invasive diagnostic investigation of the human eye. Especially the retina including cone and rod photoreceptor cells as well as blood vessels and nerve fibers, is of interest for early diagnosis of various diseases.

The retina is scanned by a weak laser through the eye’s pupil. In the considered imaging modality, nterferometric measurements of the back-scattered light allow for resolving in-depth structures along the laser beam. By changing the angle of the beam a three-dimensional analysis of the tissue is possible. During passage through the eye’s structures anterior to the retina (mainly the cornea, the lens and the vitreous body), the propagation of the laser light is perturbed due to irregularities of the refractive index, causing a loss of information by blurring in the scientific imaging process. For the correction of these perturbations, an adaptive optics (AO) system is installed. It consists of wave-front sensors that measure the phase delays of the distorted light, deformable mirrors for compensation of these delays and a unit for data processing and control of the mirrors.

Sketch of the AO supported ophtalmoscope. The main goal is to increase the quality of the resulting 3D-scans with respect to e.g. spatial resolution, avoidance of artefacts and acceleration of the whole examination process. Image Courtesy: Elisabeth Brunner, MUW

In collaboration with the Center for Medical Physics and Biomedical Engineering at the Medical University in Vienna, we try to exploit in this SFB synergies between ophthalmoscopy and astronomical imaging with extremely large telescopes (ELTs). Since adaptive optics is also utilized in these telescopes, our team has expertise in this field from cooperation with ESO and other institutions contributing to the ELT. Our first goal is to modify one of our control algorithms established in telescopic AO control and test it in the AO supported ophtalmic devices of the Vienna group. This algorithm (CuReD) has the advantage to run very fast and stable. Another area of research is the question, if it could pay off to replace the established sensor type (Shack Hartmann) by the newer pyramid sensor: This might have advantages due to the higher sensitivity of the pyramid sensor, since the laser for scanning the retina has to be of very low power to avoid damages to the eye.

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