[Substance analytic studies of the effectiveness of laser coagulation in diabetic retinopathy]

An order to optimize photocoagulation in diabetic retinopathy, it is necessary to have objective criteria concerning substance-specific fundus changes like blood, melanin, xanthophyl, cytochrome aa3, and light scattering. By means of fundus reflectometry macular reflectance spectra can be measured and are different in normals and in diabetics before or after treatment. If logarithmic difference spectra are used only pathological alterations or changes caused by the coagulation are demonstrable. These difference spectra can be approximated by a linear model function containing the extinction spectra of the substances mentioned above and a term for light scattering. Spectra deconvolution delivers coefficients, describing differences in the substance concentrations between diabetics before and after treatment and age-matched normals. When we examined these coefficients, we found that neither their behavior in diabetic retinopathy nor their reaction to photocoagulation is unique. Thus, it might be possible to obtain references to patient-specific adapted coagulation by deconvolution of the macular reflectance spectra measured before treatment. Classification of the patients in specific types of reaction, according to the shape of the logarithmic difference spectra or the results of the spectra deconvolution, could be a step in deciding on the success of the therapy on a case-to-case basis.