Biomedical subjects

P R van den Biesen

Publications and source records attributed to P R van den Biesen.

6 recordsLinked to original sources

PubMed2000

Hold up of dye in the arm during fluorescein angiography: a quantitative demonstration.

PURPOSE: To demonstrate a hold-up of part of the fluorescein bolus in the arm as a result of arm position. METHOD: Case report. We obtained a fluorescein angiogram with a calibrated confocal scanning laser ophthalmoscope in a 20-year-old healthy subject. During and after injection, the upper arm was held in approximately 60 degrees abduction, 65 degrees exorotation, and slight anteflexion. In the late venous phase, the subject moved the upper arm on the injected side to a more neutral, downward position. RESULTS: We measured a distinct rise in fluorescence level about 10 seconds after movement of the arm. The most likely explanation is relief of a partial obstruction of the venous drainage, which had been caused by the position of the upper arm described above. CONCLUSION: Impaired venous drainage of the injected arm caused by exorotation and abduction of the upper arm is a potentially common cause of delayed dye arrival or unexpectedly reduced contrast level during fluorescein angiography. Therefore, arm position needs attention in fluorescein angiography.

Adult↗

PubMed2000

Endoillumination during vitrectomy and phototoxicity thresholds.

AIM: To assess the retinal phototoxicity hazards of and to provide safety margins for endoillumination during vitrectomy. METHODS: The absolute power and spectral distribution from various light sources and filter combinations that are commercially available for vitreous surgery were measured. The maximal exposure times based on the ICNIRP safety guidelines for photochemical and thermal injury of the aphakic eye were calculated. Additionally, the effect of various measures that reduce the risk of phototoxicity was evaluated. RESULTS: Measurements of the spectrum and energy indicated that the ICNIRP safety guidelines for photochemical retinal damage are exceeded within 1 minute for nine out of 10 combinations tested. With an additional 475 nm long pass filter, light levels below 10 mW, and a distance from light probe to retina of at least 10 mm, the allowable exposure time can be increased up to 13 minutes. Thermal damage can be anticipated when the light probe touches the retina. CONCLUSION: Commercially available light sources for endoillumination during vitrectomy are not safe with respect to photochemical retinal damage. Even with maximal precautions macular phototoxic damage remains a factual danger during vitrectomy.

Hot Temperature↗

PubMed1997

Dye extravasation and the nature of background fluorescence in sodium fluorescein angiography.

PURPOSE: To obtain better insight into the process of dye extravasation in the human choroid during sodium fluorescein angiography of the ocular fundus. METHODS: Sodium fluorescein angiography using a scanning laser ophthalmoscope was performed on the right eye of five healthy volunteers. The dose of sodium fluorescein was chosen to avoid quenching in the ocular vessels. The time-intensity curve of background fluorescence was measured and its shape compared with that of the time-intensity curve of a retinal artery, representing an intravascular compartment. Significant dye extravasation is expected to cause a marked change in shape of the time-intensity curve of background fluorescence as compared with the intravascular time-intensity curve due to long washout of dye from the interstitial space of the choroid. RESULTS: In all five subjects, the time-intensity curve of background fluorescence and the retinal artery proved to be quite similar in shape until several seconds after peak intensity of the first bolus passage. CONCLUSION: Background fluorescence originates mainly from intravascular compartments during the early phase of the sodium fluorescein angiogram.

Adult↗

PubMed1985

Evolution of benign concentric annular macular dystrophy.

In 1974, Deutman described a family with an autosomal dominantly inherited macular dystrophy that he termed "benign concentric annular macular (bull's-eye) dystrophy." Ten years later, we performed a follow-up examination. Some patients complained of deterioration of visual acuity, night vision, and color vision. The macular dystrophy had progressed. The fundus periphery was more involved and in two patients there were bone corpuscle-like pigmentations. Electrophysiologic examination showed increased photoreceptor dysfunction with equal involvement of the rod and cone system. The patients had an acquired type III blue-yellow color vision defect with pseudoprotanomaly.

Adult↗

PubMedDate not supplied

Shear rate and hematocrit dependence of fluorescence from retinal vessels in fluorescein angiography.

The purpose of this work was to obtain more quantitative knowledge about the yield of fluorescence from retinal vessels during fluorescein angiography. The influence of shear rate, concentration of sodium fluorescein, hematocrit, and layer thickness on the yield of fluorescence from blood were investigated. Measurements were performed in vitro on samples of human blood in a cone-plate shear chamber using frontal illumination. Application of physiologically relevant levels of shear (> 88/sec) decreased the yield of fluorescence from the blood sample considerably as compared with stasis. The yield of fluorescence was proportionally related to the logarithm of the sodium fluorescein concentration in blood up to a sodium fluorescein concentration of 1.2 mg/ml. Above that concentration quenching occurred. An increase in layer thickness at a hematocrit of 45% resulted only in an increase of the yield of fluorescence up to a layer thickness of 25 microns. In conclusion, the sodium fluorescein concentration in blood is the only important factor that determines the yield of fluorescence from the larger retinal vessels in the successive phases of the fluorescein angiogram in a subject with a given hematocrit and hemoglobin concentration. The yield of fluorescence from retinal vessels (> 25 microns) is proportionally related to the logarithm of the sodium fluorescein concentration over a broad range of concentrations.

Biophysical Phenomena↗

PubMedDate not supplied

Yield of fluorescence from indocyanine green in plasma and flowing blood.

The purpose of this work was to obtain more quantitative knowledge about the yield of fluorescence from retinal vessels during indocyanine green angiography (ICG). The yield of fluorescence from blood was investigated for various shear rates, concentrations of ICG, and layer thicknesses. Measurements were performed in vitro on samples of human blood in a cone-plate shear chamber using frontal illumination as in scanning laser angiography. In blood and in plasma, the yield of fluorescence of ICG increased with concentration up to 0.05 and 0.1 mg/ml, respectively. At higher concentrations, the yield decreased for all layer thicknesses. For increasing layer thicknesses, both in plasma and in blood, the yield of ICG fluorescence increased nonlinearly for concentrations higher than 0.012 mg/ml. Saturation occurred for layers thicker than 200 microns in combination with ICG concentrations of 0.4 mg/ml and higher. Application of shear rates within the physiological range of the microcirculation (88/sec and 528/sec) increased the yield of fluorescence from the blood sample compared with stasis. The high transparency of blood for the excitation and emission light of ICG that was demonstrated will lead to superposition of fluorescence from superficial and deeper layers. This superposition precludes quantitative indocyanine angiography of ocular vessels.

Biomechanical Phenomena↗