Light paths in retinal vessel oximetry

Abstract

The oxygen utilization and, therefore, the metabolic state, of a distinctive area of the retina may be calculated from the diameter of the supplying artery and vein, the haemoglobin oxygenation, and the velocity of the blood. The first two parameters can be determined by imaging spectrometry at the patients ocular fundus. However, the reflected light emerging from a vessel followed different pathways through the ocular fundus layers and the vessel embedded in the retina. The contribution of the single pathways to the vessel reflection profile is investigated by a Monte Carlo simulation. Considering retinal vessels with diameters of 25-200 microm we found the reflection from a thin vessel to be determined by the single and double transmission of light at 560 nm. The backscattering from the blood column determines the reflectance in the case of a thick vessel. However, both components are in the same order of magnitude. This has to be considered in the calculation of the oxygen saturation of blood in retinal vessels from their reflection spectra.

Retinal oximeter for the blue-green oximetry technique

“…When a small spot of laser light is directed onto a blood vessel in the eye, there are many possible paths it can traverse. [26][27][28][29][30] Two paths of particular interest for this discussion are: (i) light specularly reflected from the blood vessel (also known as a glint) and (ii) laterally scattered light that has interacted with the red blood cell-packaged hemoglobin in the vessel and scattered back out of the eye. Figure 1(a) shows an example of the specular vessel glint path and Fig.…”

Imaging polarimetry and retinal blood vessel quantification at the epiretinal membrane

“…5 Optimal imaging and analysis techniques are required to obtain the clear images of the retinal blood vessels in the abnormal retina, since the complex light-tissue interactions are inherent in retinal vascular images. 6 The wavelength of illuminating light in retinal images has been emphasized as a factor influencing the contrast of retinal vessels. 7,8 In a study using a monochromatic fundus camera, the small retinal blood vessels had good contrast at wavelengths between 510 and 570 nm.…”

Monte Carlo model for studying the effects of melanin concentrations on retina light absorption

“…The basic Monte Carlo simulation process has been reported in detail elsewhere [13,14]. The photons were scattered and absorbed while propagating inside the tissue.…”