Adaptive optics
AO Group
Jörgen Thaung, jorgen.thaung@oft.gu.seZoran Popovic, zoran@oft.gu.se
Per Knutsson, per.knutsson@oft.gu.se
The AO Group performs research in the field of Multi-Conjugate Adaptive Optics (MCAO) applications for retinal imaging.
This project is supported by the Marcus and Amalia Wallenberg Foundation and De Blindas Vänner i Göteborg.
Wide-field adaptive optics instrument
Clinical retinal imaging is limited by the wavefront aberrations of the human eye. The introduction of adaptive optics (AO) in retinal imaging has been successful in correcting for most aberrations and enabling diffraction limited imaging, although this can only be accomplished over small fields of view (FOV). This is due to the fundamental limitation of conventional single-conjugate AO (SCAO) with only one retinal guide star (GS) and one deformable mirror (DM), enabling good correction close to the GS. Full correction is not achieved as one moves away from the retinal position of the GS, thereby decreasing image quality. The well corrected FOV is called the 'isoplanatic patch'.
Dicke (Astrophys J. 198, 605-615, 1975) proposed and Beckers (ESO Conference and Workshop on Very Large Telescopes and their Instrumentation. Garching, Germany, 1988)
later developed the concept of multi-conjugate adaptive optics (MCAO)
as a means of increasing the size of the isoplanatic patch for
astronomical imaging. The principle of MCAO is to accomplish this by
optically conjugating several DMs to different altitudes in the
atmosphere. In ophthalmology this is equivalent to conjugating the DMs
to different planes in the eye.
The technique of MCAO is just emerging. The first physical implementation in a large-scale astronomical
observatory was achieved in March 2007 when the Multi-Conjugate
Adaptive Optics Demonstrator (MAD) achieved 'First Light' at the ESO
Very Large Telescope (VLT). MAD allowed the scientists to obtain
corrected images over the full 2x2 arcminute FOV, substantially larger
than the 15x15 arcsecond FOV of conventional AO systems - a corrected
FOV increase by a factor of 8.
There are only a few published papers on MCAO for the eye (see e.g. Bedggood et al., Opt. Express. 14, 8019-8030, 2006; Bedggood et al., J. Biomed. Opt. 13, 024008, 2008).We have developed a closed-loop MCAO
demonstrator with two DMs, i.e. a dual-conjugate adaptive optics (DCAO)
system, for wide-field high-resolution retinal imaging on a cellular
level. The system resolution limit is ~2 microns over a retinal
field of 7x7 deg. (click here to download a PDF version of our paper from Optics Express).
Below are sample images, obtained with our instrument, from normal subjects that show; the foveal cone photoreceptor mosaic (Image 1), parafoveal capillaries (Image 2, IOVS paper), the blind spot rim capillaries (Image 3), and major bloodvessels and superficial capillaries of the retinal nerve fiber layer (Image 4). Move your mouse pointer over the images to obtain a close-up. The zoom function is realized with
Magic Zoom™ from Magic Toolbox.
Foveal cone mosaic structure (registered sum of two images) covering 5.5 x 5.5 deg.
7 x 7 deg image parafoveal capillaries, depicting the foveal avascular zone
7 x 7 deg image of blind spot rim capillaries
14 x 12 deg photomontage of four images showing major blood vessels and superficial capillaries of the retinal nerve fiber layer (blind spot situated just above to the left of this image)
Publications:
Thaung J, Knutsson P, Popovic Z, Owner-Petersen M. Dual-conjugate adaptive optics for wide-field high-resolution retinal imaging. Opt Express. 2009 Mar 16;17(6):4454-67.Popovic Z, Knutsson P, Thaung J, Owner-Petersen M, Sjöstrand J. Noninvasive imaging of human foveal capillary network using dual-conjugate adaptive optics. Invest. Ophthalmol. Vis. Sci. 2011 April 22; 52(5):2649-55.