Biomedical subjects

T T Berendschot

Publications and source records attributed to T T Berendschot.

16 recordsLinked to original sources

PubMed2001

The value of electrophysiology results in patients with epilepsy and vigabatrin associated visual field loss.

PURPOSE: To determine the value of electrophysiological findings in patients with temporal lobe epilepsy and to relate these findings to the amount of concentric contraction of the visual field and the use of vigabatrin. METHODS: Electro-retinograms and electro-oculograms were done on 30 patients, operated for temporal lobe epilepsy. The patients were divided into three groups: (A) concentric contraction of the visual field associated with a history of vigabatrin medication (15 patients), (B) normal visual field with vigabatrin use (11 patients) and (C) normal visual field without vigabatrin medication (4 patients). RESULTS: Electrophysiological abnormalities were found in 50% of the patients in group A. The Arden ratio of the EOG was lowered in 57%. Abnormalities in the ERG were found: b-wave implicit time photopic F was prolonged (50%), b-wave amplitudes scotopic B (53%), C (73%) and G (50%) and photopic H (50%) were diminished. The amount of visual field loss and the total dose of vigabatrin used, showed only slight correlation with the ERG and EOG. The use of vigabatrin during the ERG and EOG recording in group A, gave a higher b-wave amplitude scotopic G in 64% of cases. The a-wave implicit times scotopic G (73%) and photopic G (59%) and H (73%) were shortened in group B. CONCLUSION: EOG was abnormal in 57% in group A. ERG abnormalities could only be found in 50% of group A, mainly in the inner retina. Since also the total dose of vigabatrin and the amount of visual field loss did not really show a correlation with the electrophysiological findings and results of literature are not unanimous, electrophysiology does not appear at present to be a good method to detect patients with, or at risk of, vigabatrin associated visual field loss. Regularly performed visual field examination remains the cornerstone in screening.

Adult↗

PubMed2001

Visual field loss associated with vigabatrin: quantification and relation to dosage.

PURPOSE: To describe the correlation between visual field loss and the duration, dosage, and total amount of vigabatrin (VGB) medication in a group of patients with epilepsy. Co-medication of antiepileptic drugs (AEDs) and compliance were also studied. METHODS: Ninety-two patients (53 male and 39 female) taking VGB medication in the past or the present, attending the Outpatient Epilepsy Clinic in Utrecht, were examined with the Goldmann perimeter. The amount of visual field loss was calculated by the Esterman grid method and by a new method, with which the percentage surface loss of the visual field is measured. A complete drug history was compiled, specifying the amount and duration of VGB medication. Concomitant AED medication was noted. Serum levels of AEDs were determined. RESULTS: Linear regression showed the total amount of VGB as the most significant parameter to predict visual field loss (p < 0.001). Further, men were more affected than women (p = 0.026). Compliance was good, and other AEDs did not influence the results. CONCLUSIONS: Because prolonged use of VGB medication is correlated with the amount of visual field loss, VGB should be prescribed only when there are no alternatives. In such cases, we recommend an examination of the peripheral visual field before starting therapy and a repeated examination every 6 months.

Adult↗

PubMed2000

Concentric contraction of the visual field in patients with temporal lobe epilepsy and its association with the use of vigabatrin medication.

PURPOSE: To describe concentric visual field loss found in the presurgical evaluation of patients with drug-resistant temporal lobe epilepsy and relate the findings to potential causative factors. METHODS: A series of 157 consecutive patients with drug-resistant temporal lobe epilepsy, who had been selected for neurosurgical treatment, was examined in a study set up as a prospective investigation of their visual fields, to document the loss of visual field resulting from surgery. Pre-as well as postoperative visual field examinations were performed following a standard protocol using static and kinetic perimetry. As a number of patients appeared to have an unexplained concentric visual field contraction in the presurgical examination, a relation with potentially causative factors was analyzed in a cross-sectional study of all these patients. Correlations were sought with duration and severity of the seizure disorder, underlying pathology as indicated by magnetic resonance imaging (MRI) and demonstrated by pathology, any type of antiepileptic drug (AED) ever prescribed, and gender. RESULTS: In this cross-sectional analysis of 157 consecutive patients who were candidates for surgery for temporal lobe epilepsy, absolute concentric contraction of the visual field of 10 to 30 degrees was found in the presurgical examination in 20 (17%) of 118 patients who had ever used vigabatrin (VGB) and in none of 39 who had not had this medication. This difference was significant (p = 0.004). In addition, men [15 (21%) of 72] were significantly more often affected (p = 0.007) than women [five (6%) of 85]. The degree of visual field loss, as indicated by the Esterman grid, showed a positive correlation with the duration of VGB medication. There was no correlation of visual field contraction with a history of meningitis as potential cause of the epilepsy, duration of the epilepsy, status epilepticus in the medical history, or histologic abnormality of the brain tissue removed. Ophthalmologic examination of the patients with concentric contraction revealed no abnormalities. None of the patients with concentric contraction complained spontaneously of their visual field loss. CONCLUSIONS: VGB medication is a causative factor in concentric visual field loss. Visual field examination of patients using VGB should be seriously considered.

Anticonvulsants↗

PubMed2000

Long term changes in the visual fields of patients with temporal lobe epilepsy using vigabatrin.

AIM: To study the long term changes in the concentric contraction of the visual field in patients with temporal lobe epilepsy on vigabatrin medication. METHODS: Repeated Goldmann visual field examinations were compared in 27 patients with drug resistant temporal lobe epilepsy and concentric contraction of the visual field. Two groups were studied: 16 patients who had already stopped vigabatrin medication before surgery and 11 patients who continued vigabatrin medication. RESULTS: Concentric contraction of the visual field did not change in 16 patients who stopped vigabatrin before the first examination; there was slight but significant progress in visual field loss in 11 patients who continued the use of vigabatrin. CONCLUSION: Long term follow up of concentric contraction in this selected group of patients indicates that vigabatrin associated visual field loss is not reversible and that progression is possible when vigabatrin is continued.

Anticonvulsants↗

PubMed2000

L/M cone ratios in human trichromats assessed by psychophysics, electroretinography, and retinal densitometry.

Estimates of the relative numbers of long-wavelength-sensitive (L) and middle-wavelength-sensitive (M) cones vary considerably among normal trichromats and depend significantly on the nature of the experimental method employed. Here we estimate L/M cone ratios in a population of normal observers, using three psychophysical tasks-detection thresholds for cone-isolating stimuli at different temporal frequencies, heterochromatic flicker photometry, and cone contrast ratios at minimal flicker perception--as well as flicker electroretinography and retinal densitometry. The psychophysical tasks involving high temporal frequencies, specifically designed to tap into the luminance channel, provide average L/M cone ratios that significantly differ from unity with large interindividual variation. In contrast, the psychophysical tasks involving low temporal frequencies, chosen to tap into the red-green chromatic channel, provide L/M cone ratios that are always close to unity. L/M cone ratios determined from electroretinographic recordings or from retinal densitometry correlate with those determined from the high-temporal-frequency tasks. These findings suggest that the sensitivity of the luminance channel is directly related to the relative densities of the L and the M cones and that the red-green chromatic channel introduces a gain adjustment to compensate for differences in L and M cone signal strength.

Color Perception↗

PubMed2000

Slow optical changes in human photoreceptors induced by light.

PURPOSE: The basic assumption of fundus reflection densitometry is that changes in reflectance are solely determined by photolysis and regenerating visual pigments. This study was undertaken to investigate small but systematic deviations from this rule. METHODS: Spectral reflectance changes (450-740 nm) of the fovea were measured during light and dark adaptation over a period of 66 minutes in five healthy subjects. The directional properties of the fundus reflection were examined with a custom-built scanning laser ophthalmoscope (SLO) at 514, 633, and 790 nm. The same instrument was also used to find the spatial distribution of the reflectance changes. RESULTS: In addition to fast changes consistent with visual pigment, slower reflectance changes (lasting 10-20 minutes) were observed at all wavelengths including 740 nm. Because visual pigment does not absorb at 740 nm, a second mechanism must be involved. Factor analysis generated two factors (i.e., spectral curves) that explained more than 97% of the variations in the time course of the spectral reflectance. Total reflectance was modeled by means of an existing model for fundus reflection, and it was found that the first factor strongly resembled the rapid changes in absorption of the cone pigments. The second factor seems linked to slow changes in cone reflectance. Measurements with the SLO showed a clear increase in directionally dependent reflectance from 6 to 30 minutes in the dark. This was observed only in the central 6 degrees of the retina. CONCLUSIONS: The characteristics of the slow reflectance changes all point to the cone photoreceptors as the origin. Most likely, alterations in the index of refraction between the interphotoreceptor matrix and photoreceptors lie at the base of this hitherto unknown phenomenon.

Adult↗

PubMed2000

Influence of lutein supplementation on macular pigment, assessed with two objective techniques.

PURPOSE: Macular pigment (MP) may protect against age-related macular degeneration. This study was conducted to determine the extent of changes in the macular pigment density as a consequence of oral supplementation with lutein. A second purpose was to compare two objective measurement techniques. METHODS: In the first technique, reflectance maps were made with a scanning laser ophthalmoscope. Digital subtraction of log reflectance maps and comparison between the foveal area and a 14 degrees temporal site provided MP density estimates. In the second technique, spectral fundus reflectance of the fovea was measured with a fundus reflectometer and analyzed with a detailed optical model, to arrive at MP density values. Eight subjects participated in this study. They took 10 mg lutein per day for 12 weeks. Plasma lutein concentration was measured at 4-week intervals. RESULTS: After 4 weeks, mean blood level of lutein had increased from 0.18 to 0.90 microM. It stayed at this level throughout the intake period and declined to 0.28 microM 4 weeks after termination. Measurement of the density of MP showed a within-subject variation of 10% with MP maps and 17% with spectral reflectance analysis. MP density showed a mean linear 4-week increase of 5.3% (P: < 0.001) and 4.1% (P: = 0. 022), respectively. CONCLUSIONS: Supplementation with lutein significantly increased the density of the MP. Analyzing reflectance maps with a scanning laser ophthalmoscope provided very reliable estimates of MP.

Adolescent↗

PubMed1998

Photoreceptor function in unilateral amblyopia.

We investigated whether photoreceptor function in amblyopic eyes differed from that in non-amblyopic eyes. Photoreceptor function was assessed with the optical Stiles-Crawford effect (SCE), psychophysical SCE, and foveal visual pigment density in both eyes of ten unilateral amblyopic subjects. Optical SCE and density measurements were carried out with a custom-built scanning laser ophthalmoscope (SLO). Amblyopic and normal eyes did not differ in Stiles-Crawford effect, nor in foveal visual pigment density. Contrary to suggestions in the literature, we found no indication of retinal dysfunction at the level of the cone photoreceptors in amblyopic eyes.

Adolescent↗

PubMed1998

Schiotz tonometry for glaucoma: are there simple alternatives?

In the period from October 1991 until August 1992, 864 eye-patients in a rural area in south-east Nigeria were examined in order to find simple parameters for the screening of glaucoma simplex. Schiotz tonometry was used as the gold standard. Investigation of the pupil-reaction with a torch, estimation of the pressure of the (closed) eye by digital palpation, and estimations of the cup/disc ratio by ophthalmoscopy can be used as an alternative.

Adolescent↗

PubMed1998

A comparison of the optical Stiles-Crawford effect and retinal densitometry in a clinical setting.

PURPOSE: To compare the measurement of the optical Stiles-Crawford effect (SCE) to the densitometry of cone visual pigments in a clinical setting. Both tests provide information on outer retinal integrity, but the optical SCE can be performed in far less time. METHODS: Images acquired with a custom-built scanning laser ophthalmoscope were used to assess visual pigment density and optical SCE. Visual pigment density was regarded as the "gold standard." More than 100 patients with suspected, and some with known, outer retinal pathology were tested. The group included cases of central serous detachment, cone dystrophy, Stargardt's disease, Best's disease, and retinitis pigmentosa. RESULTS: Parameters of the optical SCE of 25 healthy subjects and 106 patients were taken through a stepwise linear regression to predict density. The correlation between predicted density from the optical SCE and the measured density was 0.82. The sensitivity of the optical SCE to detect decreased density was 96%. When only the foveal reflectance was considered, sensitivity was still 84% CONCLUSIONS: The optical SCE is a sensitive and fast method for detecting cone photoreceptor disturbances.

Adult↗

PubMed1997

Local photoreceptor alignment measured with a scanning laser ophthalmoscope.

The aim of this study was to develop a fast test for local photoreceptor alignment. Photoreceptor alignment is an important indicator of retinal integrity. Digitized images of fundus reflectance were obtained for 20-30 pupil entry positions with a custom built scanning laser ophthalmoscope (SLO). The data permitted the calculation of curve peakedness of the optical Stiles-Crawford effect (SCE) as a function of retinal location. We found that the peakedness is low in the central 0.5 deg, reaches a maximum at an eccentricity of 1-2 deg and gradually drops with increasing eccentricity. These data are in conformity with the anatomy of foveal cones. Additionally, the psychophysical SCE was measured with red light and an 8 deg stimulus. The mean peak position of the SCE in the pupil plane for both methods was similar, but the optical SCE was clearly steeper. The SLO provides a fast, reliable and objective way to determine local receptor alignment in the central retina.

Adolescent↗

PubMed1997

On the Stiles-Crawford effect with age.

PURPOSE: To determine whether the Stiles-Crawford effect remains stable after subjects have aged 30 years. METHODS: The relative luminous efficiency as a function of pupil position (Stiles-Crawford effect) was determined for the same seven subjects on the same apparatus in the 1960s and in 1995. The pupil opening was traversed nine times, at 20 degrees azimuth intervals. Data were fit with a revolution paraboloid yielding a peak position (x0, y0) and a peakedness (rho). RESULTS: Two of seven subjects showed a significant, but small, decrease in rho, and the other five showed, no change. No clear outcome in x0, y0 changes could be reported because of differences in pupil dilation then and now. CONCLUSIONS: Although exceptions are found on the stability of the Stiles-Crawford effect with age, the authors can still conclude that it is stable.

Aged↗

PubMed1996

Foveal cone mosaic and visual pigment density in dichromats.

1. Optical reflectance spectra of the fovea were measured in ten subjects with normal colour vision, ten protanopes and seven deuteranopes. Four conditions were used: perpendicular and oblique angle of incident and reflected light on the retina, both in a dark-adapted and a fully bleached state. 2. The spectra were analysed to assess the effects of dichromacy on the cone mosaic. A replacement model, i.e. one where the total number of cones remains unchanged and all cones are filled with a single type of pigment, was found to fit our data best. 3. The analysis of the spectral fundus reflectance also provided estimates for densities of photo-labile and photo-stable retinal pigments and fraction of long wavelength-sensitive (LWS) cones. Visual pigment density was 0.39 for protanopes and 0.42 for deuteranopes, significantly lower than the 0.57 found for colour normals. Macular pigment density was 0.54 for colour normals, 0.46 for protanopes and 0.42 for deuteranopes. 4. For colour normals the LWS cone fraction was 0.56, in agreement with psychophysical literature. The LWS cone fraction for protanopes was -0.04, and for deuteranopes 0.96, consistent with their Rayleigh matches.

Color Vision Defects↗

PubMed1996

The pathways of light measured in fundus reflectometry.

We measured the spectral reflectance of the fovea of ten normal subjects in four conditions, i.e. under dark-adapted and bleached conditions and at two retinal angles of incidence. The objective was to study optical pathways through the photoreceptor layer, resulting in a model that simultaneously explains spectral, directional and bleaching properties of the fovea. On theoretical grounds, we propose that small reflections from the stack of discs in the cone outer segments are the origin of the directional component of foveal reflection. Non-directional reflection occurs at the inner limiting membrane and at all layers posterior to the outer segments. With four reflectance spectra as input, the model allows determination of the density of the photostable absorbers, the lens, macular pigment, melanin and blood. Because of the simplified modeling of the layers posterior to the photoreceptor layer, the values for the density of melanin and blood are not necessarily comparable to physiological data. The density of the visual pigment calculated with this model is consistent with psychophysical data, with estimates for the ten subjects ranging from 0.41 to 0.80. The long wavelength sensitive cone fraction is calculated as 0.56.

Blood↗

PubMed1996

Origin of tapetal-like reflexes in carriers of X-linked retinitis pigmentosa.

PURPOSE: To determine the origin of the tapetal-like reflex (TLR) in carriers of X-linked retinitis pigmentosa. METHODS: Spectral fundus reflectance of carriers of X-linked retinitis pigmentosa was measured and compared with that of normal subjects. The influence of visual pigment was determined by measuring the density difference, that is, the difference between the logarithmically scaled spectra of a bleached and a dark-adapted retina. In addition, fundus reflectance maps at 514 nm were made with a scanning laser ophthalmoscope in a bleached and a dark-adapted condition. Finally, the optical Stiles-Crawford effect was measured to determine the angular sensitivity of the TLR. RESULTS: The tapetal-like reflex showed its spectral fingerprint in a high reflectance for wave-lengths smaller than 600 nm. The density difference measured at retinal sites of TLR was significantly larger than in normals, but the shape of the spectrum was similar. The optical Stiles-Crawford effect showed a similar peakedness for all retinal positions. However, in the TLR region, the amplitude of the directionally dependent part was increased dramatically. For the foveal region, no differences were observed. CONCLUSIONS: An increase in reflectance of the outer segments of the photoreceptors in heterozygotes compared to normals can explain both the high-density difference and the large amplitude of the Stiles-Crawford effect. An earlier suggestion that only cones contribute to the TLR is unlikely.

Adult↗

PubMedDate not supplied

A retrospective analysis of heparin-surface-modified intraocular lenses versus regular polymethylmethacrylate intraocular lenses in patients with uveitis.

BACKGROUND: Several studies described the benefits of the heparin-surface-modified intraocular tens (HSM IOL) with regard to the reduced inflammation in routine extracapsular cataract extractions. However, limited information is available about the advantages of the HSM IOL in patients with an intraocular inflammation. AIM: To assess the eventual benefits of the HSM IOL compared to the regular polymethylmethacrylate intraocular lens (PMMA IOL) in patients with uveitis. METHODS: A retrospective study of 43 patients with uveitis of various origins who underwent an extracapsular cataract extraction (24 with HSM, 19 with PMMA IOL). The activity of intraocular inflammation, visual acuity, eventual complications, and medications were examined. Standardized follow-up dates were used (before surgery, one and fourteen days, five and eleven months after surgery.) RESULTS: No difference in the inflammatory, activity was noted between HSM and PMMA groups; neither at short term clinical evaluation, nor at five months after surgery. Despite a slightly better visual acuity in the HSM group before surgery, no long term differences were observed. After surgery the increase in visual acuity was similar for both groups, as well as the frequency of cystoid macular oedema (CMO) and synechiae. Fewer patients in HSM group required Nd:YAG posterior capsulotomy, but the difference was not significant. CONCLUSION: No clinical advantage was found when the HSM IOL was compared with the regular PMMA IOL in 43 patients with uveitis.

Adolescent↗