AOSLO represents one of the most advanced retinal imaging instruments developed to date. Here the aberrations of the human eye are corrected by an adaptive optics system allowing diffraction limited imaging of the retina in healthy and diseased subjects resulting in precise mapping of cone and rod photoreceptor mosaics in vivo. The most commonly used AOSLO systems implement confocal illumination and detection. This allows the efficient capture of the photons back-scattered from the focal plane as well as rejection of out of focus photons. The main limitations of this “standard” detection scheme include successful imaging of mostly highly scattering / reflecting structures (photoreceptors, nerve fibers, and vasculature). In reality, however, most of the retinal neural tissue is highly transparent, making it hard to image with AOSLO. Additionally, use of any extrinsic contrast agents is usually very restricted due to potential toxicity of the dyes and patient discomfort limiting its application. Recently, impressive progress has been made in the visualization of vascular perfusion with AOSLO by calculation of standard deviation maps of image sequences. Despite this success, more progress is needed and any research that explores ways to further increase contrast in AOSLO retinal imaging is of great importance to the field. The work presented here by Sulai et al. focuses just on this topic.
The basic idea for the contrast enhancement methods presented here comes from a detection method proposed recently by Chui from Stephen A. Burns Lab in Indiana University. Specifically, Sulai et al. compared changes in contrast of retinal micro vasculature imaged by an AOSLO system with confocal illumination and non-confocal detection including five different detection schemes: circular mask, annular mask, circular mask with filament, knife-edge and split-detector. Additionally, the authors provided a simple interpretation of the distribution of light on the retina’s conjugate plane allowing explanation of some of the findings across the different detection schemes.
In summary, the authors conclude that the visualization of capillary flow and structure provided by AOSLO split-detection shows great promise for studying ocular micro-vasculature. They also state that image plane non-confocal split-detector method demonstrated here is just one of many contrast enhancement methods used in microscopy and they hope for future translation of other microscopy techniques into ophthalmoscopy.
Thalangunam Krishnaswamy S.
07/09/2014 12:55 AM
It made a good reading from microscopy to ophthalmoscopy.
03/30/2014 9:50 PM
Active or adoptive optics;incoherent digital holography
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