PubMed Health⌕ Search

Biomedical subjects

Márta Janáky

Publications and source records attributed to Márta Janáky.

12 recordsLinked to original sources
PubMed2007

Hypobaric hypoxia reduces the amplitude of oscillatory potentials in the human ERG.

PURPOSE: To explore the retinal functions in healthy volunteers during acute hypoxic exposure, applying a set of electrophysiological tests. METHODS: Standard electroretinograms (ERGs) of the retina (rod-(scotopic) ERGs, cone-(photopic) ERGs, maximal responses and oscillatory potentials (OPs)) and 30-Hz flicker ERGs were recorded according to ISCEV (International Society of Clinical Electrophysiology of Vision) recommendations in 14 healthy volunteers during a 15-min exposure to a simulated altitude of 5500 m. RESULTS: The mean arterial oxygen saturation level was significantly reduced (P < 0.001) during the hypobaric challenge. It returned to the normal level very shortly after the end of the hypoxic exposure. No significant change in the latency or amplitude of the slow components of the ERG was found in any recording. The OPs of the ERG, however, revealed a significant decrease in amplitude during hypoxic exposure. Both OP1 and OP2 amplitudes were significantly different (P < 0.05) from the baseline values during hypoxia. Partial recovery of these waves occurred after termination of the hypoxia. CONCLUSIONS: These results appear to support the notion that the inner layers of the retina presumed to be the main source of the OPs, display the highest sensitivity towards circulatory and/or hypoxic challenges.

Adolescent↗
PubMed2007

Multifocal ERG reveals several patterns of cone degeneration in retinitis pigmentosa with concentric narrowing of the visual field.

PURPOSE: To analyze multifocal ERGs (mfERGs) in patients with retinitis pigmentosa (RP), with constricted visual fields and visual acuity satisfactory for steady fixation. METHODS: The mfERGs of 86 eyes of 43 patients with various forms of inheritance and durations of RP were analyzed. A retinal scanning system with a 20-in. monitor was used to map central cone function. Electrical signals of the retina were detected by using DTL fiber electrodes. RESULTS: The site of the best response density of the mfERGs in the patients with RP was found in a central or eccentric position of the trace array. Depending on the position of the best response density in the two eyes, the patients were categorized into three groups. In the first group, the best response density was recorded from the central hexagon in both eyes, producing a central peak surrounded by very low responses in the three-dimensional presentation. In the second group of patients, the best responses were found to correspond to the central hexagon on only one side. In the fellow eye, however, the best response density appeared to be in an eccentric position. The patients in the third group did not present a central peak in the mfERG on either side. In scattered parts of the trace arrays, several acceptable responses were observed in all three groups that might represent patches of functioning retinal cone receptors. CONCLUSIONS: The results suggest highly variable central responses and groups of cones with preserved function in areas previously considered nonresponsive. The high variability of the central responses could be a result of variable foveal cone density, with differences in inheritance- and duration-related cone degeneration at the time of the examination. The authors stress the value of step-by-step analysis of the trace array of the mfERGs, which can reveal the still-functioning groups of cones.

Adolescent↗
PubMed2006

[Parallel processing of visual information].

This is a survey on the function of parallel visual pathway with a special emphasis on its clinical implications. It is based on data in the literature and own results of our group. The paper primarily deals with the X, Y, W pathways and by the magnocellular, parvocellular and koniocellular visual pathways characterized by cells of various size as well as by nerve fibers of various thickness. Electrophysiological, microelectrode recording of single-unit activity makes the distinction between the pathways available in animal model. Much more difficulties arise if we intend to characterize the pathways in humans or to detect the selective damage of one of these pathways in patients. The non-invasive diagnostic methods that could be used in the diagnosis are detailed here, too. Finally, the neurological, ophthalmological and psychological diseases are discussed in which a selective damage of any visual pathway is suspected. Summing it up, the survey provides evidences for the introduction of the novel concept of parallel pathways into the diagnostic aspects of ophthalmology, neurology and psychiatry.

Humans↗
PubMed2006

Electrophysiological findings in patients with nonarteritic anterior ischemic optic neuropathy.

OBJECTIVE: Nonarteritic ischemic optic neuropathy (NAION) is one of the most frequent causes of sudden visual loss in middle-aged or elderly patients. Although several electrophysiological methods are available for an objective evaluation of the visual deficits, these are not generally used in the assessment of the clinical condition of NAION patients. To evaluate the severity of the optic nerve and retinal damage, electrophysiological tests were performed on 8 patients with NAION. METHODS: Visual evoked potentials (VEPs), scotopic, photopic and flicker electroretinograms (ERGs), multifocal ERGs and pattern ERGs were recorded. RESULTS: The results demonstrated that the VEPs fairly reliably reflected the visual loss caused by NAION. The VEPs were extinguished in cases with a serious visual acuity loss, while a decrease in amplitude and a lengthening of the P100 latency were observed in cases with good visual acuity and a severe visual field loss and in the nonattacked fellow eye of the patients with monocular involvement. The pattern ERGs failed to show signs of retrograde degeneration. The photopic, scotopic and flicker ERGs, and the oscillatory potentials (OPs) were close to normal in these NAION patients. CONCLUSIONS: Our observations permit the conclusion that electrophysiological methods can provide an objective indication of the clinical condition of these patients. The new data obtained promote an understanding of the pathomechanism of the disease. SIGNIFICANCE: Electrophysiological tests are suitable for monitoring of the progression of the disease in NAION patients.

Adult↗
PubMed2005

[Experience in 13-year follow-up of a melanocytoma of the optic nerve head].

Thirteen years ago, a 35-year-old woman was found on routine ocular examination to have a pigmented tumor in her right eye, adjacent to the optic nerve head. The appearance of her fundus was suggestive of a melanocytoma. Her visual acuities were RE: 1.0 and LE: 1.0. Ultrasound examination revealed that the tumor diameter was 4.4 mm on the base and the maximal thickness was 2.7 mm. Fluorescein angiography showed a persistent hypofluorescence of the lesion. There were several additional examinations (e.g. determination of the visual field, measurement of the intraocular pressure, detection of visually evoked potentials, CT scan and MRI examination) to exclude a benign tumor of similar appearance, The patient underwent ocular examination every year. During the observation period a minor tumor enlargement occurred but there were no changes in the visual acuities. In the last two years minor signs of malignant transformation were found. The findings documented and illustrated here suggest that our methods were useful to differentiate the melanocytoma from a malignant melanoma, and no surgical interventions were needed to characterize or to remove the tumor. In addition, our patient has had good vision during the past 13 years.

Adult↗
PubMed2005

Non-arteritic ischaemic optic neuropathy (NAION) in patients under 50 years of age.

PURPOSE: The goal of our study was to compare the case histories and clinical findings in three young patients (aged<50 years) who had undergone their first attack of non-arteritic ischaemic optic neuropathy (NAION). We intended to consider whether NAION at a relatively young age might comprise a separate pathological and diagnostic entity. RESULTS: All three cases revealed some common characteristics. All of them experienced recurrent attacks with bilateral manifestations that led to severe loss of vision and visual field defects. The patients had also suffered from diabetes mellitus for a long time, but none of them had diabetic retinopathy. CONCLUSION: The case histories of these relatively young patients showed some differences, including recurrences and more severe loss of vision, to those of elderly patients. However, all the signs we found had been reported previously, although much less frequently, in NAION cases among elderly patients. The clinical and laboratory findings definitely exclude the possibility of an alternative diagnosis. Hence, our results do not support the notion of a different pathomechanism of NAION at a young age and its existence as a separate disease entity.

Adult↗
PubMed2004

[New chapter in the study of visual evoked potentials--clinical application of the multifocal VEP method].

The multifocal visual evoked potentials are the evoked responses over the visual cortex in response to the stimulation of circumscribed small areas in the central 30 degree region of the retina. The recording of multifocal visual evoked potentials was made possible by the computer algorhythm elaborated by Sutter in 1991. Multifocal electroretinography, developed upon the same theoretical principles, is already an routine clinical examination method for the topographic analysis of functional damages in the central part of the retina and for the differential diagnostics in neuro-ophthalmology. The multifocal visual evoked potential, however, has not been introduced into the clinical practice, although it displays the function of ganglion cells in a given region of the retina in a more detailed way than the sensitivity threshold in the perimetry. This examination makes the objective verification of defects possible in the visual pathway, too. In our department the recording of multifocal visual evoked potentials was started in 2002. In this paper we present the basics of this method and also deal with the problems concerning its application and its status in the history of visual evoked potentials.

Electroretinography↗
PubMed2003

The scotopic low-frequency spatial contrast sensitivity develops in children between the ages of 5 and 14 years.

The purpose of this study was to investigate the development of visual contrast sensitivity (CS) in children between 5 and 14 years of age. Six spatial frequencies and static (0 Hz) and dynamic (8 Hz) conditions were used at photopic and scotopic luminance levels. The results revealed significant maturation of CS, which reached the adult-like values by 11-12 years of age. The development was more pronounced at low spatial frequencies (<2 cycles/degree) and in the dynamic condition. The scotopic CS exhibited slower development than the photopic CS. These results suggest the late maturation of the magnocellular visual pathway.

Adolescent↗
PubMed2003

Human scotopic spatiotemporal sensitivity: a comparison of psychophysical and electrophysiological data.

The aim of the study was to investigate spatiotemporal visual functions under scotopic and photopic conditions in order to acquire human psychophysical and electrophysiological data that are comparable with contrast sensitivities based on single-unit recordings in animal experiments. Static and dynamic contrast sensitivities (CSs) and steady-state visual evoked potentials (VEPs) were measured under photopic and scotopic conditions in healthy volunteers. The results from the CS experiment indicated that the inclusion of temporal modulation and the application of scotopic luminance levels uniformly resulted in a relatively increased sensitivity for low spatial frequencies. Similarly, analysis of the second harmonic component of the VEPs demonstrated a shift from band-pass to low-pass functions. These results suggest that, under scotopic conditions, human visuospatial processing is characteristically predominated by the functional activity of the magnocellular pathways.

Adolescent↗