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Salihah Qaysi, Brian Vohnsen; Exploring directional retinal light scattering using a digital micromirror device. Invest. Ophthalmol. Vis. Sci. 2018;59(9):662.
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© ARVO (1962-2015); The Authors (2016-present)
The purpose of this study is to examine the capabilities of a digital micromirror (DMD) device as an amplitude reconfigurable pupil for the analysis of directional scattering. We provide proof-of-principle of its operation and discuss possible diagnostic applications.
We previously reported on the use of an adaptive optics (AO) fundus camera using a four-faceted glass pyramid for differential detection of cone photoreceptor pointing (Qaysi et al., ARVO Imaging in the Eye, 2017). Here, the refractive pyramid is replaced by a DMD (Vialux V-7001) which allows for rapid reconfigurations of the effective pupil for amplitude apodization and differential imaging. The AO system uses a deformable mirror (Mirao-52e) and a near-IR laser (850 nm) as guide star. Time-sequential high-resolution fundus images of healthy subjects’ eye have been captured as short video sequences (33 fps) with an sCMOS camera using a fibre-coupled LED (660 ± 12.5nm). Different pupil configurations are explored including quadrant, half circle, and annular apertures. Brightness differences of cones, blood vessel walls, and the optic nerve are used to quantify the relative angular tilts representative of oblique light scattering.
Results of captured images are shown and analysed for the peripheral retina with examples of the cone photoreceptor mosaic, blood vessel walls and the optic nerve. The structured pupil obtained with the DMD is used to calculate differential images that highlight directional scattering. The results obtained resemble phase contrast images and enhance the visibility of irregular structures. In terms of the cones, differences are small, but for blood vessel walls and the optic nerve head differences are more significant and can improve contrast by more than 50%.
The DMD is an attractive alternative for structured pupils in retinal fundus imaging as they allow for rapid reconfigurations that alter the imaging conditions. This may have diagnostic potential for imaging of retinal diseases that perturb the healthy structure of the retina including the detection of small drusen in AMD and structural changes to the optic nerve caused by glaucoma.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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