Biomedical subjects

Dietrich Schweitzer

Publications and source records attributed to Dietrich Schweitzer.

5 recordsLinked to original sources

PubMed2006

Retinal pigment epithelium cell damage by A2-E and its photo-derivatives.

PURPOSE: A2-E, a major component of the retinal pigment epithelium (RPE) lipofuscin, is a compound that can neither be degraded by nor eliminated from cells and is toxic as well as phototoxic to the cells. Illumination of A2-E with short wavelength light results in isomerization, photooxidation, as well as photolysis. Cytotoxic intermediates (free oxygen radicals) and reaction products (peroxides) are involved in this process. METHODS: A2-E solution (1.28 mM in ethanol or 10 microM phosphate-buffered saline) was kept in dark, exposed to blue light (450-490 nm, 0.2 mW/mm2) for 15 min, or to white light (8.9 mW/mm2) for 60 min, respectively and supplemented to the culture medium of primary porcine RPE cells for 24 h. Damaged cells were determined by staining with propidium iodide in 24 experiments. The photooxidation products of A2-E were analyzed by ultraviolet-visible spectroscopy and MALDI-TOF mass spectrometry. RESULTS: Supplementation of A2-E for 24 h resulted in a rate of damaged cells of 28%. Blue light exposure of A2-E before supplementation increased the rate to 91% whereas the exposure to high dosage white light reduced it to 14%. Irradiation of A2-E resulted in a dosage-dependent addition of one through four oxygen atoms. CONCLUSIONS: The increase of the cell damage rate by A2-E irradiated with low dosage light supports the hypothesis of direct DNA damage by oxidized A2-E. Furthermore, we found a reduced cell damage rate from intensively irradiated A2-E resulting in a tetraoxidized molecule which was rather stable and thus less toxic.

Animals↗

PubMed2005

Sodium fluorescein as a retinal pH indicator?

Retinal neovascularization is a symptom associated with various diseases revealing ocular fundus manifestation. Often, these neovascularizations originate from retinal hypoxia. A concomitant phenomenon of hypoxia is acidosis. To recognise this would permit the identification and treatment of hypoxic fundus areas long before first vascular modifications are seen. Thus, the goal of this investigation was to elucidate whether sodium fluorescein could be used as a retinal pH indicator. Sodium fluorescein solution was diluted in PBS (ratio: 1:150,000). The pH was varied from 6.5 to 8.6 by supplementation of HCl or NaOH, respectively. The fluorescence was excited by a pulsed diode laser (wavelength: 446 nm, pulse width: 100 ps) and detected by time-correlated single photon counting (TCSPC) technique. A least-squares fit of the measured fluorescence decay versus time by an exponential function results in the fluorescence lifetime. Ten measurements were taken at each pH for statistical analysis. The dependence of the fluorescence lifetime on the temperature and the concentration of sodium fluorescein was investigated in the same way. The fluorescence lifetime was found to rise from 3.775 ns to 4.11 ns with increasing pH (6.5 to 8.6). However, the gradient decreases with increasing pH. We found highly significant differences (Student's t-test, P<0.0005) of the fluorescence lifetimes for pH values with a mean difference of 0.125 at pH<7.65 whereas the differences were still significant (P 7.65 and mean pH differences of 0.2. The fluorescence lifetime was independent of the temperature (22 degrees C to 37 degrees C) and the concentration of sodium fluorescein (dilution 1:150,000 to 1:2000). The fluorescence lifetime of sodium fluorescein depends on the pH but not on temperature and concentration. Thus, the discrimination of areas with retinal acidosis should be possible by combination of the TCSPC technique with scanning laser ophthalmoscopy. Further investigations have to clarify whether the accuracy of the measurement at the fundus in vivo is sufficient.

Acidosis↗

PubMed2002

A simple algorithm for in vivo ocular fundus oximetry compensating for non-haemoglobin absorption and scattering.

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%.

Algorithms↗

PubMed2002

Quantitative reflection spectroscopy at the human ocular fundus.

A new model of the reflection of the human ocular fundus on the basis of the adding-doubling method, an approximate solution of the radiative transport equation, is described. This model enables the calculation of the concentrations of xanthophyll in the retina, of melanin in the retinal pigment epithelium and the choroid, and of haemoglobin in the choroid from fundus reflection spectra. The concentration values found in 12 healthy subjects are in excellent agreement with published data. In individual cases of pathologic fundus alterations, possible benefits to the ophthalmologic diagnostics are demonstrated.

Algorithms↗

PubMedDate not supplied

In vivo measurement of time-resolved autofluorescence at the human fundus.

An experimental setup for measurement of time-resolved autofluorescence of the human eye fundus is demonstrated. The method combines laser scanning technique and time-correlated single photon counting. The light source is a laser diode, delivering pulses of about 100 ps duration at a repetition rate of 40 MHz. The excitation wavelength is 446 nm and the cutoff wavelength of fluorescence detection is at 475 nm. The autofluorescence can be determined with a spatial resolution of 80 x 80 microm2 and 25 ps time resolution. The fluorescence decay is optimally approximated by a biexponential model. The dominating lifetime tau1 is shortest in the macula (320 to 380 ps) and reaches 1500 ps in the optic disk. The lifetime tau2 varies between 2 ns and 5 ns, but the spatial distribution is more homogeneous. Respiration of 100% oxygen for 6 min leads to changes in the fluorescence lifetime pointing to detection of coenzymes. Diagrams of lifetime tau2 versus tau1 are well suited for comparison of substances. Such lifetime clusters of a 20 deg macular field of a young healthy subject and of a patient suffering from dry age-related macular degeneration overlap only partially with tau2-tau1 clusters of lipofuscin.

Algorithms↗