Dual Wavelength Confocal Adaptive Optics Scanning Laser Ophthalmoscope (AOSLO)

Abstract

Purpose: : To facilitate in-vivo study of retinal function at cellular level and improve retinal imaging fidelity.

Methods: : We designed an AOSLO with two low coherence light sources of wavelengths 680 nm and 840 nm. The two beams share the same scanning optics and adaptive optics (AO), but are independently controlled by acousto-optical modulators (AOM). Two photo-detectors were optimized for photon detection in two scanning channels. The 840 nm source produced real-time retinal images with enhanced brightness, contrast and spatial resolution; while the 680 nm source presented AO corrected light stimuli on the retina. The positions of the source, the retinal plane and the photo-detector were aligned to be conjugate with each other in both channels. The eye’s longitudinal and transverse chromatic aberrations between 680 nm and 840 nm were minimized by adjusting the 680 nm source and its detector, ensuring that both beams focus transversely and longitudinally on the same point of interest in the retina.In high resolution functional imaging, where precise placement of visible light stimuli on the retina is required, the position of interest can be defined in real-time using images taken with the 840 nm source.To achieve compound wavelength imaging, the beams from the two light sources were modulated so that they alternately presented on the forward and return path of each scanning cycle thereby scanning the same retinal area quasi-simultaneously at 30 frames/second. The images formed by the two beams were separately recorded, registered and added.

Results: : The dual confocal AOSLO can deliver and maintain a stimulus on a single cone in real time by precisely tracking the eye movements. With an imaging field of view of 1.2⁰, the 3-D positioning precision of the light stimulus in the retina of a macaque eye is 0.21 X 0.21 X 27 micron³; while in the human eye, the accuracy is 1.3 X 1.3 X 60 micron³. Wavelength compounding with two low coherence light sources was readily realized.

Conclusions: : The dual source - retina - detector confocal scheme is a key for presenting a precise light stimulus in 3-D retinal space and achieving compound wavelength retinal imaging which can further reduce the interference artifacts in retinal images.

Keywords: imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • retina • image processing