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Biomedical subjects

D Papakostopoulos

Publications and source records attributed to D Papakostopoulos.

At least 19 recordsLinked to original sources
PubMed1998

Changes in psychophysiological processing of vision in myasthenia gravis.

OBJECTIVE: To investigate the possibility of impaired central nervous system (CNS) cholinergic transmission in myasthenia gravis (MG), and the effect of eye movements and particularly of micromovements in the psychophysiology of vision. MATERIALS AND METHODS: Fourteen patients with clinical manifestations of external ophthalmoplegia due to different causes (nine patients with myasthenia gravis and five with ocular myopathy) were examined. Simultaneous recording of eye movements (optical method) and pattern reversal-visual evoked potentials (PR-VEPs) were performed. RESULTS: Eye micromovements during fixation were impaired in both groups. A statistically significant difference (P < 0.01) was found in the amplitude of P100 of PR-VEPs before and after treatment in MG patients, and also between normal controls and MG patients before (P < 0.001) and after treatment (P < 0.01). P100 latency of the PR-VEPs in MG patients before and after treatment was delayed compared to normal controls, while there were no differences between ocular myopathy patients and normal controls. CONCLUSION: The eye movement impairment observed in MG patients is not sufficient to explain abnormal PR-VEPs detected in these patients. These results provide neurophysiological evidence of impaired cholinergic transmission in the central nervous system in patients with MG and suggest that PR-VEPs offer an easily applicable non-invasive method to study the central effects of MG.

Adult↗
PubMed1998

Telematic electrodiagnosis from six laboratories in three European countries and one Asian country.

The results of an electrodiagnostic test, the electro-oculogram, recorded under standardized conditions, were compared. Recordings were obtained from 70 normal subjects in three European countries and 28 subjects in an Asian country. All subjects were 18-34 years old. Equal numbers of male and female patients were tested in each of six laboratories. There were no significant differences between the results of the European laboratories. There were, however, significant differences between the results of the European and the Asian laboratories, and between the results from the male and female subjects in all laboratories. This suggests the need for considering the possibility of male/female as well as local variations in normal control values when telemedicine is applied on a global scale.

Adolescent↗
PubMed1997

Dermatomal SEPs--a complementary study in evaluating patients with lumbosacral disc prolapse.

We investigated the value of Dermatomal Somatosensory Evoked Potentials in 24 patients with unilateral radiculopathy due to lumbosacral disk prolapse. All patients had clinical signs and symptoms of disk prolapse and positive findings on neuroradiologic testing. We assessed the latency and the amplitude of the first positive waveform of Dermatomal SEPs, as well as conducting peripheral nerve conduction studies and electromyography. Our studies showed a clear correlation of Dermatomal SEP abnormalities and radiculopathy in up to 83.3% of subjects studied. Use of electromyography testing provided this correlation in about 62.5% of the same subjects. On the basis of these results, we propose that Dermatomal SEPs have value in complementing the routine electrophysiological testing of the patients with radiculopathy and provide a sensitive non-invasive technique for defining the level of disk prolapse.

Adult↗
PubMed1997

Comprehensive standardized ophthalmic telemedicine.

The Electrodiagnostic Neurophysiological Automated Analysis (ENAA) telematic system was developed in the EU EUREKA project. To validate the system 2500 electrodiagnostic tests were administered in a standardized manner during a three-year period. The tests were performed on 70 normal subjects and 500 patients in five laboratories in three European countries. The data were transmitted to the Bristol Telematic Electrodiagnostic Centre in the Bristol Eye Hospital. Data from normal subjects were not significantly different between laboratories. Data from patients were reported upon and the conclusions transmitted to the place of origin. The system provided the remote consultant with multimedia data, including medical images such as colour fundus photography and angiography, video and sound.

Humans↗
PubMed1996

The scotopic electroretinogram to blue flashes and pattern reversal visual evoked potentials in insulin dependent diabetes.

Pattern reversal visual evoked responses (PR-VEPs), the electroretinogram (ERG) to blue flashes of light in dark adaptation, the steady state ERG to 40 Hz flicker, and alterations in pupil diameter following dark adaptation were studied in 56 juvenile onset diabetics, 34 of whom had no ophthalmoscopic or photographic evidence of diabetic retinopathy (DR-group). The remaining 22 had mild background retinopathy (DR+group). Normal data was obtained from 24 subjects matched for age and sex with diabetics. Skin electrodes were used for all recordings. The scotopic 'b' wave of the ERG was significantly lower in amplitude in the DR- diabetics and it was even more reduced in the DR+group. The PR-VEP was significantly delayed in diabetics but there was no difference between the two groups. The steady state ERG was not significantly different between normals and diabetics. These findings indicate that retinal and more central abnormalities develop early in diabetics. Detection of objective electrophysiological abnormalities may be used to identify persons at risk of developing retinopathy and to monitor the effects of treatment.

Adolescent↗
PubMed1996

Telematic electrodiagnosis.

Using the Electrodiagnostic Neurophysiological Automated Analysis (ENAA) telematic system, 1560 standardized electrodiagnostic tests have been performed on 70 normal subjects and 320 patients in five laboratories in three European countries. The data from each patient have been transmitted from the five satellite laboratories to the Bristol Telematic Electrodiagnostic Centre (BRITEC), housed in the Bristol Eye Hospital, where they were evaluated and the conclusions transmitted to the place of origin. The results from the normal subjects were not significantly different between laboratories. Also patients with specific types of disease had similar results in all laboratories. The results from both the normal subjects and the patients show that a working prototype for providing telematic electrodiagnosis is available and has been well received by both clinicians and patients.

Adult↗
PubMed1995

Electro-oculographic abnormalities in amblyopia.

BACKGROUND: Electrodiagnostic tests have been used to investigate retinal function in amblyopia but previous results have been conflicting. METHODS: It was decided to investigate whether the electro-oculogram (EOG) showed any abnormalities in 12 adult amblyopes and 12 age and sex matched controls with normal vision. The mean amplitudes of the EOG recordings from each eye during 12 minutes of darkness and 18 minutes of light were compared. RESULTS: The mean values from the amblyopic eyes were lower than those from the fellow non-amblyopic eyes. At most time points the difference was significant (p < 0.05). After normalisation of the data to minimise intersubject variation, the reduction in EOG amplitudes of the amblyopic eyes at all time points was significant (p < 0.05). There was no significant difference between the mean values obtained from the right and left control eyes at any time point, either before or after normalisation. CONCLUSIONS: These results provide evidence for a retinal abnormality in amblyopia and implicate the retinal pigment epithelium as being involved. A deficiency in retinal dopaminergic function in amblyopia is proposed as a possible mechanism causing these results.

Adult↗
PubMed1994

Electrodiagnostic evaluation of the visual system: the role of the clinician.

Visual electrodiagnosis is a new discipline with a long history. The foundations include the disciplines of psychophysics, neurophysiology, electronics, computer science, statistics and medicine. However, with such a complex heritage, visual electrodiagnosis has taken a considerable time to evolve to its present form. Today visual electrodiagnostic assessment is relevant, not only for conditions primarily affecting the visual system, but also in more generalised pathological states in which eye changes may be a manifestation. Pressures for more refined and accurate diagnoses stem both from a continuing improvement in knowledge of disease processes by the medical profession and greater expectations on the part of patients seeking advice. Specialised investigative services such as electrodiagnosis, if these are appropriately funded and maintained, provide data to clinicians which is repeatable and objective, without resorting to invasive technology.

Adult↗
PubMed1994

Optimised averaging by on-line statistical verification of response in clinical electrodiagnostic trials.

Real time statistical verification of the averaged response in many established electrodiagnostic tests may result in a substantially reduced number of presented stimuli thus minimising the test's duration and reducing the overall time load on the patient examined. Furthermore, a sufficient number of stimuli may be automatically established in an objective statistical way by accounting for the response amplitude and variance, noise amplitude etc., resulting in averages with matching signal to noise ratio. A technique of real time statistical verification of the response based upon single trial data analysis was developed and verified in clinical electroretinographic (ERG) tests.

Dark Adaptation↗
PubMed1994

Pattern reversal visual evoked potentials in retinitis pigmentosa.

Pattern reversal visual evoked potentials (PR-VEPs) of 31 patients with retinitis pigmentosa (RP) and 20 normal control subjects were recorded and compared. Recordings were taken from Oz referred to Fz, by stimulating with squares subtending 60 min, presented at a visual field of 30 degrees and 98% contrast. The mean latency of the main positive component P100 of the PR-VEP of the RP patients was 116.1 msec (SD 12.71) and 114.84 after stimulation of the left and right eye respectively. These values are significantly different (p < 0.001) from the equivalent values of the normal controls (102.5 ms (SD 5.1) and 100.6 ms (SD 4.6) for the left and right eye, respectively). Fourteen patients had a P100 latency more than 3 SDs from the normal mean value. Subsequently the patients were classified into three groups (for each eye separately) according to visual acuity (VA) and comparison for PR-VEP amplitude and latency was performed. In group A patients with VA 6/6, in B with 6/9 and in G with 6/12 or more were included. Decrease of VA was significantly associated with increased latency. The amplitude was not significantly affected except for group C. All 3 groups were not significantly different in age. The P100 in group A was consistently prolonged, compared to normals. It seems that RP can introduce significant increase in the PR-VEP latency associated with decreased VA. This may have diagnostic and prognostic implications.

Adolescent↗
PubMed1993

The Farnsworth-Munsell 100 hue test in the first episode of demyelinating optic neuritis.

The Farnsworth-Munsell 100 hue test (F-M 100) was used to examine 30 patients with their first episode of unilateral demyelinating optic neuritis (DON) at presentation, after 6 weeks and after 6 months. Twelve patients satisfactorily completed the test with the affected eye at presentation. This number had increased to 23 by 6 weeks and to 27 by 6 months. No patient with a visual acuity of LogMAR 0.86 (Snellen equivalent approx 6/43) or worse, could complete the test. The mean total error score of affected eyes showed significant improvement at each subsequent examination but was always worse than the non-affected eyes. There was a significant correlation between total error scores and visual acuities of affected eyes at presentation and after 6 months. Fourteen patients recovered a visual acuity of LogMAR 0.0 (Snellen equivalent 6/6) or better but the total error scores of the affected eyes were significantly worse than the non-affected eyes (p = 0.017), indicating that defective colour vision is an indicator of a previous episode of DON despite the recovery of normal visual acuity. DON is reported to produce a red-green (Type II) axis of colour defect but individual F-M 100 polar diagrams were usually generally abnormal and did not show any predominance of recognisable axis of colour defect at any examination. Group averaging of the F-M 100 data from such a well-defined group of patients with acute DON revealed a significant bipolar abnormality in the tritan (blue-yellow) axis at presentation which was not demonstrated at the subsequent examinations or at any examination of the non-affected eyes.

Adult↗
PubMed1993

Clinical and infrared pupillometry in central retinal vein occlusion.

Measurements of pupillary reactivity and size were recorded using neutral density filters and infrared pupillometry (IRP) in a prospective masked study of acute central retinal vein occlusion (CRVO) to quantify the two methods of measurement and to compare their value in the prediction of rubeosis. Thirty two patients were examined within 45 days of disease onset. The mean relative afferent pupillary defect (RAPD) with filters was significantly greater in patients who developed rubeosis than in those who did not (0.9 vs 0.3 log units; p = 0.012). Using IRP, the pupillary diameters in the dark (maximum) and in the light (minimum) were significantly greater, the rate of pupillary constriction was significantly lower, and the latency of constriction was significantly greater in affected eyes than in unaffected eyes. The differences between affected and unaffected eyes in the IRP parameters of latency, rate, maximum, and minimum pupillary diameters were significantly greater in patients who developed rubeosis than in those who did not. Discriminant analysis of the IRP parameters correctly and statistically significantly identified rubeotic patients with 83% sensitivity and 95% specificity. An RAPD of > or = 0.6 log units was 83% sensitive and 70% specific in this regard. It is concluded that pupillary reactions are abnormal in many patients with acute CRVO, as measured by both pupillometric methods. The degree of these abnormalities has a relationship to the development of rubeosis, and might prove useful in planning the follow up of these patients or in deciding whether to apply panretinal photocoagulation. The neutral density filter test is readily available but subjective. IRP is more specific, objective, and suited to further development, but requires sophisticated equipment.

Aged↗
PubMed1992

The electro-oculogram in central retinal vein occlusion.

As part of a prospective masked study, the electro-oculogram (EOG) was recorded from 28 patients within 48 days of developing central retinal vein occlusion (CRVO). The EOG light peak/dark trough ratio (Lp/Dt) x 100 was significantly lower in the affected than in the unaffected eyes of patients (p < 0.001), and abnormally low in absolute terms in 20 patients (71%). All unaffected fellow eyes had a normal EOG ratio. The mean Lp amplitude of affected eyes was significantly smaller than that of unaffected eyes (p < 0.001), whereas the differences in mean Dt amplitudes between affected and unaffected eyes were not statistically significant. The Lp amplitude in the affected eye was 48% or less of that in the unaffected eye in the eight patients (29%) who developed rubeosis iridis during the 9 month follow-up, and in six others. No patient whose Lp amplitude in the affected eye was greater than 48% of that in the unaffected eye, developed rubeosis. It is concluded that the Lp amplitude is abnormal in patients with acute CRVO. The degree of this abnormality bears a relation to the development of rubeosis, which might prove a useful indicator of whether to institute or withhold panretinal photocoagulation.

Acute Disease↗
PubMed1989

Effect of N-REM sleep on the cortical SEPs in early life.

Cortical and cervical somatosensory evoked potentials (SEPs) were studied by the averaging method in twenty healthy children, aged 20 days to 3 years. The stimulus was applied to the median nerve at the wrist and SEPs were recorded by electrodes placed on to the contralateral parietal scalp region as well as over the skin at the C6-7 vertebral region. The reference electrode was placed at the Fz. All subjects were studied during the awake state as well as during the N-REM sleep. The results indicate that N-REM sleep influenced the latency and the duration of SEPs, especially in children aged less than one year. This finding probably reflects a variable rate of maturation of the somatosensory pathway. The state of wakefulness must therefore be taken into account when assessing the pathological relevance of SEP recording in young children.

Age Factors↗
PubMed1987

Comparative study of clinical and surgical findings and cortical somatosensory evoked potentials in patients with lumbar spinal stenosis and disc protrusion.

This paper is dealing with a comparative study of clinico-surgical findings and cortical somatosensory evoked potentials (CSEP's) recordings after stimulation of the right and left common peroneal nerve behind the fibula head, in twenty five patients suffering from lumbar spinal stenosis and disc prolapse. In all instances, the latencies of the first positive wave (the waveform also, when the latency was not discrete) were evaluated. The neurophysiological findings were verified by surgery. In combination with other roots, L3 root was affected in 1 patient, L4 in 6, L5 in 13 and S1 in 11. L5 was affected alone in 11 and L5 and S1 were impaired in combination in 11 patients. Seven patients presented sural atrophy. The results of the neurophysiological study are described below: There was delayed response on both sides in six patients, while in ten patients delayed response was found on one (affected) side, inconclusive responses in seven and in two normal. Myelography and CT Scan were performed pre-operatively to ascertain disc protrusion and establish stenosis criteria. The surgical findings were: clear disc protrusion in 4 patients, stenosis in one and combined lesions in 20 (including central disc protrusion in seven). Sixteen patients out of twenty-five had a follow up neurophysiological evaluation in addition to the clinical follow up examination. In thirteen of the above patients, (taken with the clinical progress) the re-examination gave improved neurophysiological data both as regards latency and P1 waveform. It was obvious that high value latencies were associated with long standing clinical symptoms while at the same time root compression involved more than one level. Regarding the neurophysiological data and the surgical findings, it was found that in the majority of the cases (92%) these two parameters matched together, so that in such cases a possible prediction of the operative outcome can be given.

Adult↗