A new method for the spatially resolved measurement of the oxygen saturation of retinal vessels is described. Imaging spectrometry was used for both measurements of transmission and reflectance spectra of whole blood in cuvettes as well as for fundus reflectance spectra. A model was developed for the calculation of the oxygen saturation, valid in the wavelength range between 510 nm and 586 nm, in that the internal reflectance is constant and only the transmitted light depends on layer thickness and hematocrit. Altogether 265 measurements were performed in different number at 30 eyes. In each measurement, the oxygen saturation was simultaneously determined for 193 locations along a line of 1.5 mm at the fundus. The mean oxygen saturation in retinal arteries was (92.2 +/- 4.1)% and (57.9 +/- 9.9)% in retinal veins. The mean retinal arterio-venous difference of the oxygen saturation was (35.1 +/- 9.5)%. The venous oxygen saturation depended on distance from the optic disc. The measured mean of the arterio-venous difference of the oxygen saturation corresponded well to the value of the brain (34%). The utilization of oxygen in the temporal quadrants (inferior: 39.4 +/- 10.4%) is significantly (p = 0.05) higher than in the nasal quadrants (inferior: 31.3 +/- 6.7%).

A highly diluted suspension of red blood cells (hematocrit 0.01) was illuminated with an Ar or a dye laser in the wavelength range of 458-660 nm. The extinction and the angle-resolved intensity of scattered light were measured and compared with the predictions of Mie theory, the Rayleigh-Gans approximation, and the anomalous diffraction approximation. Furthermore, empirical phase functions were fitted to the measurements. The measurements were in satisfactory agreement with the predictions of Mie theory. However, better agreement was found with the anomalous diffraction model. In the Rayleigh-Gans approximation, only small-angle scattering is described appropriately. The scattering phase function of erythrocytes may be represented by the Gegenbauer kernel phase function.

An algorithm is introduced for the compensation of the influence of non-haemoglobin absorption as well as tissue scattering on blood spectra used in optical oximetry at the ocular fundus. The in vivo measured spectra were corrected by a linear transformation in order to match the reference spectra of fully oxygenated and reduced blood, respectively, at three isosbestic points (522 nm, 569 nm and 586 nm). The oxygen saturation can then be determined at a wavelength showing a high contrast between oxygenated and reduced haemoglobin (e.g., 560 nm). Reflection measurements at blood flowing through cuvettes were used to validate the algorithm. The oxygen saturation values were compared to measurements of the same samples at a laboratory haemoximeter. The mean deviation was found to be 2.65%.

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The facet heating of a single-quantum well InGaAs/AlGaAs broad-area high-power laser-diodes emitting at 940 nm was reduced by the introduction of a 30 µm long current blocking region located at the front facet of the laser, also increasing the level of catastrophical optical mirror damage. The blocking of the pump current close to the facet reduces the carrier density and then the surface recombination current. The temperature rise of 2 mm long and 200 µm wide lasers is reduced by a factor of 3-4