Biomedical subjects

Anne Kurtenbach

Publications and source records attributed to Anne Kurtenbach.

9 recordsLinked to original sources

PubMed2006

L:M-cone ratio estimates of the outer and inner retina and its impact on sex differences in ERG amplitudes.

The relative number of L- and M-cones varies greatly between individuals. Differences in the relative number of L- and M-cones may also contribute to the sex difference in the ERG response amplitude reported several times. We therefore investigated the relative number of L- and M-cones and its impact on sex differences in ERG amplitudes. Multifocal ERG (mfERG) and multifocal oscillatory potentials (mfOP) combined with a cone silent substitution technique were used to investigate outer and inner retinal signals recorded from 7 female and 7 male trichromats. L:M ratios were estimated from peak amplitude as well as from area under curve (AUC) analysis. For mfERGs the L:M ratios estimates were independent of the method of analysis, while for mfOPs, differences were found which are possibly due to an artefact in the calculation of ratios for small responses. There was a tendency for lower L:M ratios in female than in male subjects for both analysis of mfERG and mfOP responses. The (L+M)-response amplitudes at both sites were slightly higher and the L:M ratios were lower for female than for male observers. Because the magnitude of the ERG amplitude differences is larger than could be explained by L:M-ratio and axial length differences, we conclude that it may be due to a direct effect of sex hormones on ion channel function.

Adaptation, Ocular↗

PubMed2005

Quantification of stato-kinetic dissociation by semi-automated perimetry.

The difference in threshold sensitivities that are found when examining the visual field (VF) with static versus kinetic perimetric methods is called stato-kinetic dissociation (SKD). In this pilot study, we describe a semi-automated procedure for quantifying SKD. Fifteen patients with VF defects were examined with kinetic and static perimetry. SKD values were defined as positive when the static scotoma was larger than the kinetic one. We found significant local variations of SKD along scotoma borders with the individual reaction time as an important criterion when determining kinetic thresholds. There was a verifiable SKD in all patients with locally negative values in eight subjects.

Adult↗

PubMed2005

Multifocal oscillatory potentials in CSNB1 and CSNB2 type congenital stationary night blindness.

We evaluated the function of the inner retina in patients with congenital stationary night blindness of the complete (CSNB1) and the incomplete type (CSNB2) by recording multifocal oscillatory potentials (mf-OPs). The VERIS system was used to record mf-OPs from 61 areas of the central retina from 5 CSNB1 patients (4 with NYX gene mutation), 6 CSNB2 patients (2 with CACNA1F mutation) and 11 control subjects. For each subject group, the first- and second-order kernel responses for one eye were analysed and the amplitudes and implicit times of their major components compared to 5 concentric rings centred on the fovea. In CSNB1 patients, the mf-OP peak amplitudes of the first-order kernel responses showed a significant reduction of the first peak without significant reduction of the second, whereas in CSNB2 both peak amplitudes were barely discernable from noise for all eccentricities. In the second-order kernel, the third peak was reduced in CSNB1 patients, and again not discernable from noise in CSNB2 patients. The difference in amplitude between the control and CSNB1 groups was significant for the late components of the first- and the second-order kernel. Implicit times were not significantly altered. The difference in mf-OP amplitude between CSNB1 and CSNB2 patients reflects the different molecular mechanisms underlying the two types of disease, which differentially affect the postreceptoral pathways of cone signal processing. The well-preserved peak 2 amplitudes of first-order mf-OPs and peak 3 amplitudes of second-order mf-OPs in CSNB1 patients point to a major impact of OFF-pathway components on these responses which are not present in CSNB2 patients. In conclusion, our results show that CSNB1 and CSNB2 are two different types of disease, not only on a genetic but also on a pathophysiological level.

Adolescent↗

PubMed2004

Inner retinal contributions to the multifocal electroretinogram: patients with Leber's hereditary optic neuropathy (LHON). Multifocal ERG in patients with LHON.

In this study we examine the multifocal electroretinogram (mfERG) recorded from patients suffering from Leber's hereditary optic neuropathy (LHON), a degeneration of the ganglion cell and nerve fibre layers of the retina. We compared the mfERGs recorded from 11 patients with LHON, to those from 11 control subjects. The pattern ERG (PERG) was additionally performed with 9 of the patients. MfERGs were recorded and analysed using the VERIS 3.01 system with a stimulus of 103 equal-sized hexagons. For analysis, hexagons were grouped according to distance from the optic nerve head (ONH) and according to distance from the fovea. Two significant differences were found between the waveforms of the two groups: In the first order kernel, the control group showed a component around 34 ms that decreased with distance from the ONH. This component was reduced in the LHON group of subjects. In the second order (first slice) kernel, the patient group was missing features that decrease with distance from the fovea in the control group. PERG amplitudes showed a significant correlation with the amplitude of the second order mfERG kernel. The results show that the damage to ganglion cells and nerve fibres caused by LHON can be detected in mfERG recordings and indicate that activity from the inner retina can contribute significantly to first and second order waveforms.

Adult↗

PubMed2002

Anomaloscope matches in patients with diabetes mellitus.

BACKGROUND: Functional visual deficits can occur in patients with diabetes mellitus who show no visible morphological alterations in the retina. In this study we examined the colour vision of diabetic patients using metameric matches. Patients with and without retinopathy, as well as those who had been treated with laser photocoagulation, were examined to ascertain how the functional alterations in the diabetic eye alter with disease status. METHODS: Rayleigh (red-green) and Moreland (blue-green) metameric matches were determined in a total of 51 diabetic patients (24 patients with no retinopathy, 12 patients with background retinopathy and 15 patients who had undergone laser therapy). Their results are compared to those of a control group of 25 subjects with normal colour vision. RESULTS: A deficit in blue-green colour discrimination found in patients without retinopathy becomes worse with the appearance of vascular alterations in the retina. There is also a significant shift towards green in the Rayleigh match midpoint and towards blue in the Moreland match midpoint, which is at least in part explicable by alterations in lens opacity. Patients who have undergone laser therapy show, on average, better colour discrimination than those with retinopathy, but there is a large variation in their results. CONCLUSION: The alterations in the colour vision of diabetics indicate that at least the early functional changes are occurring at an inner retinal location. Lens opacity changes also play a large role as the age of the patients increases.

Adolescent↗

PubMed2002

Visual field constriction and electrophysiological changes associated with vigabatrin.

PURPOSE: We investigated functional, morphological and electrophysiological changes in patients under anti-epileptic therapy with vigabatrin (VGB), a GABA aminotransferase inhibitor. METHODS: 20 epileptic patients treated with vigabatrin (age range 25-66 years) were enrolled in this study. The referrals were made by the treating neurologist, based on suspected or known visual field changes in these patients. Two patients had vigabatrin monotherapy, 18 patients were treated with vigabatrin in combination with other antiepileptic drugs. None of the patients reported visual complaints. Patients were examined with psychophysical tests including colour vision (Farnsworth D15), dark adaptation threshold, Goldmann visual fields and Tuebingen Automated Perimetry (90 degrees). A Ganzfeld ERG and an EOG following the ISCEV standard protocol were also obtained. Additionally, all patients were examined with the VERIS multifocal ERG including recordings of multifocal oscillatory potentials. RESULTS: Visual acuity, anterior and posterior segments, colour vision and dark adaptation thresholds were normal in all patients. Of 20 patients, 18 presented visual field constriction. All patients with visual field defects revealed altered oscillatory potentials waveforms in the ERG, especially in those patients with marked visual field defects. Multifocal oscillatory potentials were also delayed in those patients. In some patients a delayed cone single flash response (6/20), a reduced mERG amplitude (12/20) and a reduced Arden ratio (9/20) were found. CONCLUSIONS: The present data indicate an effect of vigabatrin on the inner retinal layers. Since abnormalities of the oscillatory potentials were seen in all patients with visual field defects a dysfunction of GABA-ergic retinal cell transmission might be assumed.

Adult↗

PubMed2002

Effect of aging on multifocal oscillatory potentials.

Multifocal oscillatory potentials (m-OPs) are thought to reflect rod-cone interactions. We examined the effect of age on the topography of the m-OP responses out to an eccentricity of 30 deg. Fifty-eight normal subjects were studied, aged between 13.6 and 58.8 yr. The data show a linear decrease in amplitude and a linear increase in latency with age, which is significant for most potentials. The decrease is uniform over the retina. These results suggest that an age-related impairment is occurring at or before the inner retina.

Adolescent↗

PubMedDate not supplied

Multifocal electroretinogram in trichromat and dichromat observers under cone isolating conditions.

The aim of this study was to obtain information about single cone class driven activity in the inner and outer retina in humans. We examined outer retinal activity with the multifocal electroretinogram (mfERG) and inner retinal activity using multifocal oscillatory potentials (mfOPs). A standard (black-white) stimulus was used, as well as stimuli aimed at isolating a single photoreceptor class. The results of 10 trichromats were compared to those of 2 protanopes and 2 deuteranopes. At both retinal layers we find that trichromats show cone isolating response amplitudes that reflect the expected number of cones and that single- gene dichromats have a similar total number of functioning cones as trichromats. The ratio of the responses of the L- and M-cones is slightly smaller for the mfOPs than for the mfERGs. The results indicate that there are major changes in the gain of retinal signals after the inner plexiform layer.

Adult↗

PubMedDate not supplied

Hyperoxia, hyperglycemia, and photoreceptor sensitivity in normal and diabetic subjects.

The aim of this study was to investigate the effects of an increase in the saturation of blood oxygen (SaO2) and/or serum glucose on photoreceptor sensitivity in normal subjects and in patients with diabetes mellitus. We monitored cone and rod sensitivity by recording dark-adaptation curves to both green and red test stimuli while inhaling either air (20% O2 + 80% N2) or 100% oxygen in 12 normal subjects and 12 diabetic patients with no (10) or mild (2) retinopathy. We also repeated the experiment in 10 of the normal subjects under hyperglycemia (mean serum glucose: 161 mg/dl). Results show that in normal subjects the dark-adapted cone sensitivity is improved by an increase in SaO2 or by hyperglycemia. Final rod sensitivity is unchanged during hyperoxia and during hyperglycemia when measured with a green test spot. However the kinetics of dark adaptation are altered during hyperglycemia, and an increase in final sensitivity is observed when measured with the red test spot. Inhalation of oxygen during hyperglycemia in normal subjects reduces cone sensitivity compared to that found during hyperglycemia alone (Pasteur effect). In diabetic subjects the dark-adapted cone threshold is comparable to that found in normal subjects, and sensitivity also increases with an increase in SaO2. The final rod threshold, however, is impaired compared to that of the control group, and rod sensitivity is improved by increasing the SaO2. The results suggest that the metabolism of rods and cones may differ in normal subjects: in cones, the rate of metabolism can be augmented by increasing the available oxygen or glucose, whereas rods appear more insensitive to increased blood oxygen saturation and hyperglycemia. In diabetic subjects, both cone and rod metabolism can be increased by supplemental oxygen, indicative of an early rod deficit. The study lends weight to the hypothesis that dark-adapted rods in diabetics are hypoxic before the onset of retinopathy.

Adult↗