PubMed Health⌕ Search

Biomedical subjects

J A Van Best

Publications and source records attributed to J A Van Best.

16 recordsLinked to original sources
PubMed2001

Corneal autofluorescence in choroidal melanoma or in choroidal naevus.

AIMS: To investigate whether corneal autofluorescence is different in patients with choroidal melanoma or choroidal naevus. METHODS: Corneal autofluorescence was determined by fluorophotometry in both eyes of 32 patients with a unilateral choroidal melanoma, 32 patients with a unilateral choroidal naevus, and 32 age matched healthy controls. The corneal autofluorescence ratio between affected and contralateral eyes of patients or between randomly selected eyes of healthy controls was calculated. RESULTS: Mean corneal autofluorescence ratio of patients with a choroidal melanoma was significantly higher than that of healthy controls (mean ratio: 1.09 (SD 0.15) and 1.00 (0.09), respectively, ANOVA p=0.014), and than that of patients with choroidal naevus (mean ratio 0.96 (0.09), p<0.001). Mean ratios of patients with choroidal naevus and healthy controls were not significantly different (p=0.27). CONCLUSIONS: Corneal autofluorescence ratio of patients with a unilateral choroidal melanoma is increased. This is probably due to an increased flow of glucose through the impaired blood-aqueous barrier in the affected eye, resulting in additional glycation of corneal proteins and hence in increased autofluorescence. The corneal autofluorescence is not increased in patients with a choroidal naevus, because the blood-aqueous barrier is not impaired in the affected eye in these patients. Measurement of corneal autofluorescence is simple, fast, and non-invasive, and might be helpful to distinguish between patients with choroidal melanoma and those with choroidal naevus.

Analysis of Variance↗
PubMed2000

Reflex lacrimation in patients with glaucoma and healthy control subjects by fluorophotometry.

PURPOSE: Steady state tear turnover (TTO), defined as TTO under normal physiological conditions, is significantly lower in patients with untreated glaucoma than in healthy control subjects. To obtain more information on the effect of glaucoma on lacrimation, a method for quantification of reflex lacrimation was developed and applied to patients with glaucoma or ocular hypertension and healthy control subjects. METHODS: After instillation of 2 microl of fluorescein (2%), the decay of fluorescein concentration in tears was measured by fluorophotometry over 10 minutes to determine steady state TTO. Then, reflex lacrimation was induced by stimulating the trigeminal nerve with ethanol vapor via the nostrils. Thereafter, the decay of fluorescein and corresponding steady state TTO were determined again. An index of reflex lacrimation, defined as the percentage decrease in fluorescein concentration as a result of stimulation, was calculated by forward and backward extrapolation of the steady state decay of the fluorescein concentration in tears, relative to the time of stimulation. RESULTS: The index of reflex lacrimation was determined in 16 patients with newly discovered but not yet treated glaucoma, 16 patients with untreated ocular hypertension, and 16 healthy control subjects. The values did not differ between groups (mean +/- SD, 67.0%+/-17.7%, 63.5%+/-21.3%, and 70.4%+/-19.6%, respectively; ANOVA, P>0.25). Surprisingly, the steady state TTO after stimulation was lower than that before stimulation in each group (ratio, 0.62+/-0.46; paired t-test, P<0.04). CONCLUSIONS: The method developed is appropriate for the quantification of reflex lacrimation. Reflex lacrimation is not influenced significantly by glaucoma or ocular hypertension. The decreased steady state TTO after reflex stimulation may be caused by exhaustion of the lacrimal glands after excessive reflex lacrimation, indicating that normal lacrimation probably also contains reflex tears.

Adult↗
PubMed1999

Autofluorescence of the diabetic and healthy human cornea in vivo at different excitation wavelengths.

Corneal autofluorescence is higher in diabetes mellitus patients with retinopathy than in healthy subjects. In this study, the excitation spectra of corneal autofluorescence of diabetic patients and healthy controls in the range 365 nm-480 nm were compared in an attempt to identify the fluorophores responsible for corneal autofluorescence in health and disease (diabetes). Spectral measurements (from one eye) were recorded from five patients with proliferative diabetic retinopathy and five age-matched healthy controls, using a modified commercial scanning fluorophotometer with a mercury arc or a tungsten halogen lamp as excitation light source in combination with interference filters (excitation wavelengths: 365, 405, 420, 430, 436, 440, 450, 470 and 480 nm; bandwidth: 10 nm). Fluorescence emission was measured in the range 532 nm-630 nm. The sensitivity of the modified fluorophotometer was calibrated by using the excitation spectrum of fluorescein as a reference. The corneal excitation efficiency of the diabetic patients was higher than that of the healthy controls at each wavelength investigated (Mann-Witney test P<0.0005). The ratio between the mean values of both groups was equal for each excitation wavelength (mean ratio 1.9+/-0.12s.d.,P>0. 2), suggesting that the excitation spectra were equal. This indicates that the same fluorophores are responsible for the corneal autofluorescence in both groups. The shapes of the excitation spectra suggest the involvement of flavins, NAD(P)H, and at least one other, as yet unidentified, fluorophore.

Adolescent↗
PubMed1999

Autofluorescence distribution along the corneal axis in diabetic and healthy humans.

Corneal autofluorescence, as measured with a commercial scanning fluorophotometer (lambda(exc): 415-491 nm; lambda(em): 515-630 nm), is increased in patients with diabetes mellitus. However, such fluorophotometers register an average fluorescence signal over all corneal layers as a consequence of their limited axial resolution of 0.5 mm. In order to determine the location of the fluorophores responsible for the increased corneal autofluorescence measured in diabetics, an attempt was made to measure in vivo the distribution of autofluorescence along the optical axis of the cornea with a modified slitlamp. Fluorescence excitation and emission filters identical to those of the scanning fluorophotometer were fitted to a slitlamp equipped with a slow scan CCD camera. Corneal autofluorescence intensity profiles were obtained with the slitlamp in five patients with severe diabetic retinopathy and compared to those of age-matched healthy controls. Corneal autofluorescence was also measured with the scanning fluorophotometer for comparison. The resolution of the CCD camera for measurement of fluorescence along the corneal axis was 0.1 mm. The corneal autofluorescence intensity of the patients and the healthy controls gradually decreased by about the same amount from the endothelium to the epithelium (57% mm(-1)+/-6 s.d. and 52% mm(-1)+/-5 s.d., respectively). The area under the fluorescence intensity curve was significantly greater for the patients than for the healthy controls (factor 2.4+/-1.0 s.d., P<0.001) and was proportional to the corneal fluorescence measured with the scanning fluorophotometer (r=0.92, P<0.001). The results show that (1) the distribution of autofluorescence along the corneal axis can be measured in vivo in humans, (2) the fluorophores involved are distributed throughout the cornea, and (3) the relative distribution of fluorescence is similar in diabetic patients and healthy controls.

Cornea↗
PubMed1998

Long term follow-up of lenticular autofluorescence and transmittance in healthy volunteers.

This study was undertaken to assess long term changes in the lenticular autofluorescence and transmittance of healthy volunteers. Both eyes of 15 healthy volunteers aged 8 to 62 years were examined by slit-lamp examination and fluorophotometric measurements of lenticular autofluorescence (lambdaexc=415 nm-490 nm, lambdaem= 510 nm-550 nm) and transmittance (lambda=415 nm-550 nm) in 1983 and 1996. The changes in lenticular autofluorescence and transmittance between 1983 and 1996 were determined and compared with those calculated on the basis of age-dependence curves of a group of 56 healthy volunteers measured in 1983. These curves were obtained by approximation of the values of the 56 healthy volunteers by a linear, polynomial or exponential function of age, respectively. A mean yearly increase of lenticular autofluorescence of 8.69 ng . equivalent fluorescein . ml-1 . year-1 was observed in the 15 volunteers between 1983 and 1996 and this increase was significantly larger than that calculated on the basis of the three age-dependence curves in 1983 (6.36, 6.47 and 6.53 ng . equivalent fluorescein . ml-1 . year-1, P=0.0026, 0.0037 and 0.0044, respectively). The transmittance showed a mean yearly decrease of 0.508% . year-1 which was significantly larger than calculated on the basis of the three age-dependence curves in 1983 (0.153, 0.220 and 0.183% . year-1, P=0. 0033, 0.012 and 0.0059, respectively). One volunteer, i.e. the individual with the highest lenticular autofluorescence and lowest transmittance in 1983, had developed cataract in 1996. These measurements demonstrate for the first time, quantitative changes in lenticular autofluorescence and transmittance in a long term follow up. The at least 35% larger increase of autofluorescence and 130% larger decrease in transmittance in the follow-up group between 1983 and 1996 in comparison with the values based on age-dependent curves in 1983 could be caused by the increased solar UV radiation in The Netherlands during that period of time.

Adolescent↗
PubMed1997

Permeability of the blood-retinal barrier in healthy humans. European Concerted Action on Ocular Fluorometry.

BACKGROUND: The aim of this study was to compare the inward permeability of the blood-retinal barrier in healthy subjects from six European cities. METHODS: Seventy-two healthy subjects (age 20-70 years) were selected. At 30 min and 60 min after fluorescein injection, fluorescein mass in vitreous was calculated from the concentrations measured along the optical axis of the eye. Non-protein-bound fluorescein (NPBF) concentrations were measured in plasma prepared from blood samples taken 7, 15 and 55 min after injection. Blood-retinal barrier permeability (PBRB) was calculated from the vitreous fluorescein mass and the time integral of NPBF and was corrected for the autofluorescence of ocular tissue and for lenticular light transmittance. RESULTS: Mean PBRB values +/- SD (nm.s-1) were 2.07 +/- 0.54 (Coimbra), 2.01 +/- 0.43 (Frankfurt), 2.24 +/- 0.50 (Ghent), 2.37 +/- 0.56 (Herlev), 1.89 +/- 0.44 (Leiden) and 1.74 +/- 0.38 (Porto). Differences between centers were not significant (P > 0.35). Measurements were reproducible and independent of the time after fluorescein injection (P > 0.50). A PBRB higher than 3.16 nm.s-1 or a value which had increased by 32% was considered abnormal (P < 0.05). CONCLUSION: PBRB values were similar in all centers. The results demonstrate that this is a highly sensitive and reliable method for measuring the permeability of the blood-retinal barrier.

Adult↗
PubMed1994

Blue-light-induced dysfunction of the blood-retinal barrier at the pigment epithelium in albino versus pigmented rabbits.

The purpose of this study was to determine the role of epithelial melanin in blue light phototoxicity of the retina. The first manifestation of the phototoxicity has been shown to be a breakdown of the blood-retinal barrier at the retinal pigment epithelium. The blood-retinal barrier function of six New Zealand albino rabbits was compared to that of four pigmented chinchilla rabbits after exposure to broad-band blue light (400-520 nm). Additionally, the spectral sensitivity of blood-retinal barrier dysfunction was determined by exposing 15 New Zealand albino rabbits to narrow-band blue light with peak intensity at lambda = 408 nm, 418 nm, 439 nm, 455 nm and 485 nm (bandwidth: 11.7-13.5 nm). The blood-retinal barrier function was evaluated with vitreous fluorophotometry. Ultrastructural changes and permeability of the retinal pigment epithelium for horseradish peroxidase were evaluated in the albino rabbits with electron microscopy. Exposure to broad-band blue light up to 832 J cm-2 demonstrated the blood-retinal barrier of albino and pigmented rabbits to be equally sensitive. Electron microscopy of albino rabbits exposed to above-threshold energy demonstrated an increase of inclusion bodies in the retinal pigment epithelium and vacuolation of the cytoplasm. Transcellular passage of intra-arterially administered horseradish peroxidase through the pigment epithelium into the subretinal space was seen. The narrow-band exposures demonstrated that light of 439 nm was more effective than the light of other wavelengths in inducing barrier dysfunction in albino rabbits. This implies that chromophores absorbing at 439 +/- 6 nm were responsible for the phototoxicity in albino rabbits. The results indicate that melanin does not have a damaging nor a protective role in phototoxicity since (1) the presence of melanin is not essential for blue-light-induced photochemical damage to the blood-retinal barrier at the retinal pigment epithelium, and (2) protection from this sort of damage is not greater in melanin containing epithelia than in non-melanin containing epithelia.

Animals↗
PubMed1993

The effect of white light and UV-A on the green autofluorescence of the rabbit lens in vivo.

The part of the light spectrum which is responsible for an increase of lenticular green autofluorescence upon white light exposure was determined for the rabbit. The increase of autofluorescence as a function of the light energy was measured, to assess a possible threshold energy for lens alterations. Thirteen rabbits (Chinchilla Greys) were used. An area of 3 or 4.7 mm2 of the lens was exposed to light from a standard tungsten halogen lamp (250 W, lambda = 360-720 nm). Wavelength selection was performed with the use of light filters. The light dose was adjusted by varying the exposure time between 15 min and 180 min. The green lenticular autofluorescence (lambda exc = 420-490 nm, lambda fluor = 530-600 nm) was measured with a fluorophotometer. A significant increase of lenticular autofluorescence after exposure was observed only if the exposure light contained high wavelength UV-A (lambda = 360-400 nm; 0.8% of the total white light energy); additional white light (without UV-A; up to 13 kJ cm-2) did not have any effect on autofluorescence. The autofluorescence returned to pre-exposure values within 4 days. No lesions could be seen on slitlamp examination. The autofluorescence after exposure to UV-A increased linearly with the exposure energy from 13 J cm-2 (14 mW cm-2 for 15 min) up to 155 J cm-2. The increase was 2.0% of the pre-exposure value per J cm-2 and the correlation coefficient 0.94, P < 0.001. A threshold energy was not found.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Dysfunction and repair of the blood-retina barrier following white light exposure: a fluorophotometric and histologic study.

The purpose of this study was to pinpoint the site of blood-retina barrier disruption after white light exposure and determine the course of barrier repair. The retinas of 25 anaesthetized pigmented rabbits were exposed for 1 hr to the light of a xenon arc lamp filtered to eliminate ultraviolet and infrared light. The light intensities selected were near the threshold intensity causing visible retinal lesions in order to evaluate the function of the blood-retina barrier (BRB) in this range. Functional assessment of the BRB was made with vitreous fluorophotometry (VF), and electron microscopy (EM) after intra-arterial administration of horseradish peroxidase (HRP) as tracer. In 11 of the 14 rabbits exposed to threshold intensity (90-110 mW cm-2; retinal field of illumination, 0.64 cm2), a breakdown of the BRB was demonstrated by a 2-40-fold increase in the permeability of the BRB for fluorescein and by transcellular passage of HRP through the retina pigment epithelium (RPE). All 11 rabbits developed oedematous fundus lesions. Within a week, pigmentary alterations of the fundus were seen on ophthalmoscopy, while the BRB permeability for fluorescein and HRP had returned to normal. EM of the retina showed slight swelling of RPE during the period of increased permeability but no alterations of the neuroretina. After functional barrier repair, the RPE cells demonstrated irregularity of the melanin pigment alignment and some loss of the monocellular arrangement. In six rabbits exposed to subthreshold light intensity (65-89 mW cm-2) no fundus lesion developed and EM evaluation of the BRB was normal.2+ remains altered.

Animals↗
PubMed1990

Light transmission of the cornea in whole human eyes.

The transmission of the cornea for light in the wavelength range 450-1000 nm was measured in steps of 50 nm by means of a photodiode implanted into the anterior chamber of whole human donor eyes. In the range from 450 nm up to 600 nm the percentage transmission was found to increase with wavelength from 80% up to 94%. In the range from 60 nm up to 1000 nm the percentage transmission was between 95% and 98%. The corneal transmission for donors younger than 45 yr (n = 3, 22-43 yr) did not differ significantly from that of donors older than 45 yr (n = 5, 67-87 yr) at any wavelength.

Adult↗
PubMed1987

Plasma fluorescein decay determination during fluorophotometry.

Two useful methods for determination of the decay curve of non-protein bound fluorescein (NPBF) in plasma up to 1 hour after intravenous fluorescein injection are described and evaluated. The course of NPBF is approximated in method 1 by a sum of two exponential decay functions and in method 2 by a power of time function. The parameters in these functions are calculated with the use of concentration values measured in two blood samples taken at about 5 min. and 60 min. after injection. Calculations in method 1 include the amount of fluorescein injected. The accuracy of each method was evaluated in 7 volunteers by measuring NPBF concentration in 15-28 blood samples taken after fluorescein injection at intervals of 5 min. or less. The mean relative deviation between calculated and measured concentration values amounted to 9.2% +/- 4.3 SD and 12.7% +/- 4.5 SD for method 1 and 2, respectively. The time integral of NPBF concentration in plasma up to one hour after injection was calculated according to the results of both methods and compared with integral values obtained by linear interpolation between concentration values measured in the 15-28 plasma samples. The mean relative deviation for the 7 volunteers amounted at 15 min. to 2.8% and 17% and at 60 min. to 11% and 18% for method 1 and 2, respectively. The maximal difference between the blood-retinal barrier permeability value for NPBF calculated with and without taking glucuronation into account was estimated to be 20% for an average glucuronation percentage of 70% or less.

Adolescent↗
PubMed1982

Comparison of thyroid function in mice after various injected activities of 123I, 125I and 131I.

The radiotoxicity of 123I, 125I and 131I to the thyroid gland was compared in groups of mice subjected to activities of the three isotopes ranging from 10(-2) to 10(2) MBq. The thyroid function was determined fifteen months later on the basis of the 24-hour uptake of a tracer activity of 131I. A reduction in uptake to 20 per cent of the control value for untreated mice was found for mice injected with 35 MBq of 123I, 13 MBq of 125I and 2 . 2 MBq of 131I. On estimating the average absorbed dose in different parts of the thyroid by means of a refined method of dose calculation, that found in the cell layers surrounding the follicles seemed to be most indicative for impairment of thyroid function.

Animals↗
PubMed1977

A one microsecond component of chlorophyll luminescence suggesting a primary acceptor of system II of photosynthesis different from Q.

The kinetics of the luminescence of chlorophyll a in Chlorella vulgaris were studied in the time range from 0.2 mus to 20 mus after a short saturating flash (t 1/2 = 25 ns) under various pretreatment including anaerobiosis, flashes, continuous illumination and various additions. A 1 mus luminescence component probably originating from System II was found of which the relative amplitude was maximum under anaerobic conditions for reaction centers in the state SPQ- before the flash, about one third for centers in the state S+PQ- or SPQ before the flash, and about one tenth for centers in the state S+PQ before the flash. S is the secondary donor complex with zero change; S+ is the secondary donor complex with 1 to 3 positive charges; P, the primary donor, is the photoactive chlorophyll a, P-680, of reaction center 2; Q- is the reduced acceptor of System II, Q. Under aerobic conditions, where an endogenous quencher presumably was active, the luminescence was reduced by a factor two. The 1 mus decay of the luminescence is probably caused by the disappearance of P+ formed in the laser flash according to the reaction ZP+ leads to Z+ in which Z is the molecule which donates an electron to P+ and which is part of S. After addition of hydroxylamine, the 1 mus luminescence component changed with the incubation time exponentially (tau = 27 s) into a 30 mus component; during the same time, the variable fluorescence yield, measured 9 mus after the laser flash, decreased by a factor 2 with the same time constant. Hereafter in a second much slower phase the fluorescence yield decreased as an exponential function of the incubation time to about the dark value; meanwhile the 30 mus luminescence increased about 50% with the same time constant (tau = 7 min). Heat treatment abolished both luminescence components. The 1 mus luminescence component saturated at about the same energy as the System II fluorescence yield 60 mus after the laser flash and as the slower luminescence components. From the observation that the amplutide is maximum if the laser flash is given when the fluorescence yield is high after prolonged anaerobic conditions (state SQ-), we conclude that the 1 mus luminescence is probably caused by the reaction PWQ- + hv leads to P*WQ- leads to P+W-Q- leads to P*WQ- leads to PWQ- + hv in which W is an acceptor different from Q. The presence of S+ reduced the luminescence amplitude to about one third. Two models are discussed, one with W as an intermediate between P and Q and another, which gives the best interpretation, with W on a side path.

Aerobiosis↗
PubMedDate not supplied

Evaluation of diabetic retinopathy by fluorophotometry. European concerted action on ocular fluorometry.

BACKGROUND: Fluorophotometric variables (permeability of the blood-retinal barrier (BRB) and blood-aqueous barrier (BAB), corneal autofluorescence, and lenticular light transmittance) are reported to correlate with the severity of diabetic retinopathy. This preliminary multicenter study was performed to measure these variables simultaneously in patients with type 2 diabetes mellitus and to assess which of these variables could be of help in evaluating diabetic retinopathy. METHODS: Eighty-two patients with type 2 diabetes and diabetic retinopathy were recruited in seven European university clinics. Each patient was investigated three times, at intervals of about one year. The investigations included fluorophotometric determination of corneal autofluorescence, lenticular light transmittance, and permeability of the BRB and BAB. Retinopathy was classified into four grades, using a simplified evaluation system based on the Modified Airlie House retinopathy classification and applied to color fundus slides of standard fields 1 and 2. RESULTS: Multiregression analyses revealed that only corneal autofluorescence and BRB permeability were correlated with the severity of diabetic retinopathy (P < 0.05). Corneal autofluorescence and BRB permeability as single variables were found to be indicative of severe nonproliferative retinopathy and proliferative retinopathy (sensitivity 100% and 86%, respectively, and specificity 65% and 85%, respectively). Combination of both variables increased specificity to 92%. CONCLUSIONS: This preliminary multicenter study shows that fluorophotometric variables can be measured simultaneously and reliably in patients with diabetes and that corneal autofluorescence and BRB permeability (individually or in combination) could be of help in detecting severe non-proliferative retinopathy and proliferative retinopathy.

Blood-Aqueous Barrier↗