Abstract
Purpose: :
Confocal Scanning Laser Ophthalmoscopy with Adaptive Optics and an Out-of-Plane design (OP-AO-CSLO) has been found suitable to image cones and rods of the in-vivo human retina. Point-spread function engineering as, for example, when changing the beam profile at the entrance pupil can increase resolution and contrast by improving the match between the probing light beam and the individual photoreceptors of a given diameter. Here, our aim is to study how the specific illumination and the selected confocal detection scheme can be used to analyze directionality and light-capture efficiency of the individual photoreceptors.
Methods: :
Rapid motorized scanning of the entrance pupil and the confocal pinhole allows analysis of photoreceptor directionality during in-vivo imaging. We have modified our in-house build OP-AO-CSLO to feature a superluminescent diode as source and explore photoreceptor directionality and confocality using motorized Z-scanning of the detection pinhole. The subject's eye pupil is dilated and accomodation is paralyzed to enhance the stability during image acquisition at 47 fps.
Results: :
The results confirm the directionality of individual cones from which a directionality parameter may be extracted and that their visibility (and reflectivity) may originate at different retinal depths. This can play a role for the temporal variations of reflectivity reported with Optical Coherence Tomography and gives added insight into the coupling mechanisms between the probing light beam and the individual photoreceptors.
Conclusions: :
The results confirm that photoreceptor light waveguiding is crucial for optimized retinal imaging aimed at resolving the individual cones and rods in vivo. Scanning the entrance pupil and pinhole during the acquisition may have clinical relevance to detect photoreceptor obliquities and possible complications in relation to the presence of drusen and macular degeneration.
Keywords: receptors • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound)