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Sabah Chetty, Steve Gruppetta; Three-dimensional True Color In-vivo Retinal Imaging Using Novel Application Of Structured Illumination. Invest. Ophthalmol. Vis. Sci. 2011;52(14):1758.
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The human retina is difficult to image in high resolution- it is a 3D non-homogeneous, non-stationary target. Existing techniques such the SLO and OCT require moving parts, lasers and complicated post-processing. This work investigates a novel use of structured illumination in a non-scanning imaging system to visualize the retina in 3D and in true color.
Structured illumination uses a high frequency fringe pattern as illumination for the retina to resolve fine details. It requires three incoherent phase-shifted sub-images which can be combined to yield good lateral and axial resolution. The design presented ensures that the frequency of the illumination pattern is not limited by the optics of the eye because the fringe pattern is projected using a modified Michelson interferometer - in comparison to existing techniques employing grid projection or coherent fringe projection. The design employs incoherent light sources at different wavelengths, each of which create their own set of Fizeau interference fringes. Three images can be taken simultaneously by separating the different wavelengths of light. Simultaneous acquisition also ensures the sub-images used to generate the high resolution image are subject to the same aberrations for the non-stationary imaging object.
A novel design for a retinal imaging device based on structured illumination is presented in detail- the Structured Illumination Opthalmoscope (SIO). Theoretical assessments show the axial sectioning capabilities of the device and results from simulations are presented to quantify the relationship between various system parameters on the axial and lateral resolution of the device. These include the frequency of the sinusoidal illumination, effect of differing reflectivity of light when collecting the sub-images at three wavelengths and the change of modulation of the fringes with defocus as a function of the geometry of the illuminating optics.
A novel retinal imaging technique, the SIO, has been presented and it has been shown theoretically to possess the same optical sectioning properties as the SLO but can potentially offer an inexpensive, optically simple alternative with fewer artifacts.
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