Biomedical subjects

J van Best

Publications and source records attributed to J van Best.

6 recordsLinked to original sources

PubMed1996

Diffusion coefficient through the blood-aqueous barrier using a standard protocol.

AIMS/BACKGROUND: Comparison of the diffusion coefficient through the blood-aqueous barrier of healthy volunteers measured in different cities with identical fluorophotometers using a standardised protocol. METHODS: Healthy volunteers aged between 20 and 70 years were studied in seven European cities. The fluorescein concentration in the anterior segment of each eye was measured with a commercial scanning fluorophotometer 30 and 40 minutes after intravenous fluorescein. The decay of non-protein bound fluorescein concentration in blood plasma was determined with the use of three blood samples taken at 7, 15, and 55 minutes after injection. The diffusion coefficient through the blood-aqueous barrier was calculated from the ratio between the fluorescein concentration in the anterior chamber and the time integral of non-protein bound fluorescein concentration in plasma using specially developed software. RESULTS: The mean values of the diffusion coefficient (SD) (X10(-4) min-1) were 4.76 (1.51) (n = 20, Brussels), 5.48 (2.33) (n = 17, Coimbra), 3.47 (2.09) (n = 12, Cologne), 6.09 (2.77) (n = 21, Frankfurt), 3.85 (1.59) (n = 11, Ghent), 4.99 (1.69) (n = 23, Leiden), and 4.87 (1.05) (n = 20, Madrid). The values between centres were similar (Kruskal-Wallis test p > 0.05) except for Cologne and Frankfurt (p = 0.013). No differences were found when repeating measurements (four centres, interval time 1-8 months, Wilcoxon paired test p > 0.39). CONCLUSION: The diffusion coefficients had similar values and standard deviations. The concerted action demonstrated the usefulness of a standardised protocol.

Adult↗

PubMed1994

Topical timolol, corneal epithelial permeability and autofluorescence in glaucoma by fluorophotometry.

UNLABELLED: Corneal epithelial permeability and autofluorescence were measured by fluorophotometry in patients with open-angle glaucoma or ocular hypertension to quantify the epithelial function of the cornea and to evaluate its metabolic activity in 24 patients using daily timolol and 11 not using timolol. The findings were compared with those in age-matched healthy controls. Permeability values in patients using timolol were 1.9 times higher than in patients not using timolol and 2.5 times higher than in healthy controls (Mann-Whitney test P < 0.001). Values for patients not using timolol did not differ from those for healthy controls (P = 0.15). Corneal autofluorescence values in each patient group were higher than in healthy controls (P = 0.002). CONCLUSIONS: (1) open-angle glaucoma or ocular hypertension alone does not affect corneal epithelial permeability; (2) daily instillation of timolol causes impairment of the corneal epithelial barrier; (3) open-angle glaucoma or ocular hypertension are likely to induce an increase of corneal autofluorescence.

Administration, Topical↗

PubMed1994

Topical timolol with and without benzalkonium chloride: epithelial permeability and autofluorescence of the cornea in glaucoma.

Epithelial permeability and autofluorescence of the cornea were determined by fluorophotometry in 21 patients with open-angle glaucoma or ocular hypertension using timolol medication with the preservative benzalkonium chloride (BAC) and 2 weeks after changing to timolol medication without BAC. The investigation was performed to determine whether removal of BAC would reduce toxic effects on the cornea and complaints of sensations of burning or dry eye. Corneal epithelial permeability decreased significantly after changing medication (mean decrease per patient 27%, P = 0.025). Corneal autofluorescence increased significantly after changing medication suggesting an alteration in corneal metabolism (mean increase per patient 6%, P = 0.003). Timolol without BAC was found to be as effective as timolol with BAC in reducing intraocular pressure (P = 0.4). Removal of BAC from timolol resulted in an improvement of corneal epithelial barrier function and in a reduction of complaints. The improvement was found to be proportional to the duration of the preceding BAC-containing therapy.

Administration, Topical↗

PubMed1992

Dysfunction of the blood-retina barrier following white light exposure. A tracer study with horseradish peroxidase and ferrous gluconate.

The aim of this investigation was to study the ultrastructural effects of white light on the retinas of pigmented rabbits. The retinas were exposed to white light (400-740 nm) at intensities between 65 and 140 mW/cm2 for 1 h. Two days after exposure, the increased leakage of fluorescein measured with vitreous fluorophotometry could be mimicked on electron microscopy by the tracers ferrous gluconate and horseradish peroxidase (HRP). In cases of minimal fluorescein leakage, traces of HRP were found in the basal folds of the retina pigment epithelium (RPE). No HRP was observed apical to the tight junctions of the RPE cells. When there was a great amount of fluorescein leakage, HRP completely filled the RPE cytoplasm, the extracellular spaces, and several cells in the neuroretina. It is concluded that after exposure to low intensities of white light, blood-retina barrier dysfunction may be due to disruption of the RPE basal fold membrane, leading to increased transcellular passage. The intact tight junctions suggest the under these circumstances intercellular leakage is not a component of BRB dysfunction.

Animals↗

PubMed1989

Blood-retinal and blood-aqueous barrier permeability, lens autofluorescence and transmission in insulin-dependent diabetic youngsters.

The permeability of the blood aqueous and blood retinal barrier, the lens transmission, and the lens autofluorescence were measured by fluorophotometry in 7 diabetic youngsters treated by conventional therapy (mean age, 10.9 +/- 4.4 years), 9 diabetic youngsters treated by continuous s.c. insulin infusion (mean age, 12.3 +/- 5.0 years), and 13 healthy controls (mean age, 12.4 +/- 5.1 years). The mean permeability value for the blood retinal barrier of the diabetic juveniles did not differ significantly from that of the controls (P greater than 0.4), and no correlation with metabolic control (HbAlc) or duration of diabetes was found (P greater than 0.1). No differences in lens transmission larger than 4% were found. The mean value of lens autofluorescence corrected for normal age-dependency was found to correlate with the metabolic control: an increase of mean HbAlc by 1% resulted in an extra increase of autofluorescence by 11% (P = 0.002). This result suggests that good metabolic control can suppress excess lens autofluorescence, a precursor of cataract.

Adolescent↗

PubMed1989

In vivo ultrasound backscattering estimation for tumour diagnosis: an animal study.

In this study the efficacy of a quantitative analysis of backscattered ultrasound for the differential diagnosis of intraocular tumours is tested. The data acquisition was performed with an on-line acquisition and processing system for in vivo work. The backscattering spectra were corrected for the beam effects (diffraction and focussing). The measurements were taken from an animal model (rabbit) in which a Greene's amelanotic melanoma was implanted in the anterior chamber of the eye. The special histologic arrangement of this tumour makes it optimally suited to an assessment of the correlation between histology and backscattering cross section. Various backscattering models were considered theoretically and the choice for a practical testing was motivated on the properties of the observed backscattering spectra. We conclude that the backscattering model based on an "inhomogeneous continuum" with a cylindrical Gaussian autocorrelation function fits the data optimally. The relatively low correlation of the backscattering cross-sections to histology cannot yet be fully explained. The range of acoustic scatterer sizes, however, corresponds quite well to the dimension of observed and quantified histologic structures.

Animals↗