Dual wavelength Scanning Light Ophthalmoscope with concentric circle scanning

Abstract

Abstract Purpose :Multispectral imaging helps in gathering important physiological parameters about the retina. We present a novel and compact scanning light ophthalmoscope (SLO) using a digital micromirror device (DMD) capable of imaging the retina at 7 Hz at two different wavelengths with a maximum 20° × 20° field of view (FOV). Methods :The dual-wavelength SLO (Fig.1) used DMD to create concentric circle scanning on the retina. The concentric circles were centred around the fovea and provided fixation. By shifting the centre of the circles to different locations on the DMD, we imaged different regions of the retina. An annulus was placed in conjugate to the pupil plane in the illumination arm to create an annular illumination on the cornea. In the detection arm, a circular aperture was used to block corneal reflections and pass only the signal reflected from the retina onto the camera. Blocking the corneal reflections reduced the background and increased the signal to noise ratio. Polarisation optics were used to discard the stray reflections within the system. Virtual pinholes were implemented in the digital to create confocal images (Heintzmann et al, 2006). To demonstrate the capabilities of our system, we imaged the right eye of a healthy volunteer with a DMD pattern projection speed of 140 Hz and a fill-factor of 1/20. We used 660 nm and 810 nm illuminations to record confocal images. Results :Fig. 2A shows the fundus photograph of the subject. Fig. 2B & 2C shows the images of the macular region with the fovea in the centre imaged using 810 nm and 660 nm. Since we used polarisation optics, the macular bowtie structure is visible in Figs. 2B & 2C. The optic nerve head region is shown in Figs. 2D & 2E for both wavelengths. Blood vessels in the perifoveal inferior region were also imaged (Fig.2F & 2G). These images show high contrast details of the retina with big and small blood vessels at two different wavelengths. Conclusions :We have demonstrated multispectral retinal imaging using a DMD to create high contrast retinal images. The DMD enables fixating the eye to different locations allowing us to image different parts of peri- and parafoveal regions. This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017. Figure1: Optical layout of the system Figure 2: Imaging in the right eye of a healthy volunteer (A) : Fundus photo. (B-G) : Confocal images of different peri- and para-foveal regions imaged by 810 nm and 660 nm denoted by coloured dotted circles. Scale bar is 5 degrees