Light path-length distributions within the retina

Abstract

Abstract. A Monte Carlo simulation of light propagation through the retina has been developed to understand the path-length distributions within the retinal vessel. For full-field illumination, the path-length distribution within the vessel comprises directly backscattered light and light that has passed once or twice through the vessel. The origins of these light path-length distributions can be better understood by investigating different combinations of single-point illumination and detection positions. Perhaps the most significant observation is that illumination at the edges of the vessel, rather than over the whole field of view, and detection directly above the vessel capture only the light that has taken a single pass through the vessel. This path-length distribution is tightly constrained around the diameter of the vessel and can potentially provide enhancements for oxygen saturation imaging. The method could be practically implemented using an offset-pinhole confocal imaging system or structured light illumination.

Holistic Monte-Carlo optical modelling of biological imaging

“…The uncertainty in oximetry due to noise-induced uncertainty in measured vascular contrast is lowest when the vascular contrast is close to 46% (corresponding to an optical density of log 10 (1/ e )) and improves with increasing signal-to-noise ratio. Inference of oxygen saturation requires however knowledge of optical path lengths through the blood, an understanding of the effects of scatter and how they interact with the imaging system 38,39 . Typically a simplified model is employed: light detected using confocal imaging is considered to have been transmitted twice through a blood vessel (the dominant reflection is normally considered to be scattering by the choroid or the sclera), whereas for imaging using a large-area detector, light is considered to be transmitted only once through a vessel.…”

Optimal wavelengths for subdiffuse scanning laser oximetry of the human retina

“…In such geometries, the blood vessel occupies majority of the probed volume. Monte Carlo simulations 39,40 have suggested that in this type of geometry with a quasiconfocal aperture, the photons reaching the detector have predominantly been backscattered from within the blood vessel. In this case, hL eff ðλÞi in Eq.…”

Multispectral oximetry of murine tendon microvasculature with inflammation

“…Annular illumination simplifies and improves the accuracy of the oximetry algorithm; with annular illumination, back-scattered light is eliminated and detected light arises only from single-pass absorption through a blood vessel. This concept has been validated for retinal vessels by Rodmell et al [16]. Simplification and improvement in the accuracy of the oximetry algorithm is hence achieved as described in section 2.2.…”