Biomedical subjects

Jelka Brecelj

Publications and source records attributed to Jelka Brecelj.

8 recordsLinked to original sources

PubMed2007

VEP asymmetry with ophthalmological and MRI findings in two achiasmatic children.

Achiasmia is a rarely diagnosed visual pathway maldevelopment where all or the majority of nasal retinal fibres fail to decussate at the optic chiasm. It has been identified by neuroimaging and also by visual evoked potential (VEP) asymmetry. VEP asymmetry has not been defined consistently in previous studies. The aim was to study VEP asymmetry to flash stimulation in two children with maldevelopment of the optic chiasm in comparison to control children. Both children had congenital nystagmus, optic nerve hypoplasia with a bilateral small double ring, bitemporal visual field defect and normal colour vision. In child 1 visual acuity in both eyes was 0.1, in child 2 it was 0.2. MRI showed reduced chiasmal size in child 1, while in child 2 it was combined with other midline abnormalities. VEP to monocular flash stimulation showed in both children distinctive occipital distribution, which was not observed in control children. The N2 wave was distributed asymmetrically over the ipsilateral hemisphere to the stimulated eye, while the P2 wave was distributed over both hemispheres. The P2 wave was however better defined over the ipsilateral hemisphere. Flash VEP occipital distribution remained similar in child 1, who was followed from 10 months to 9 years. These cases of achiasmia demonstrate a distinctive VEP asymmetry in the distribution of the flash VEP N2 wave, as well as the expected structural defect determined by neuroimaging.

Child↗

PubMed2006

Pediatric clinical visual electrophysiology: a survey of actual practice.

PURPOSE: Survey the actual clinical practice of pediatric visual electrophysiology. The electrophysiologists surveyed were members of the International Society for Clinical Electrophysiology of Vision (ISCEV). METHODS: A self-administered questionnaire with 55 items about visual evoked potential (VEP) and electroretinogram (ERG) testing of pediatric patients was sent to ISCEV members. The survey queried personnel, facilities, referral patterns and conduct of tests. RESULTS: Nearly all respondents (94%) had advanced scientific or clinical degrees or both, and most (96%) worked in academic or medical facilities. Of the 71 respondents, 68 tested patients 12 years or younger, and nearly all of those performed both VEPs and ERGs. However, fewer than a third did high volume (>10/month) testing of infants and young children (< or =6 years). Eye care professionals and neurologists made the majority (57%) of the referrals, with the most common reason for referral being suspected visual impairment. Conduct of a pediatric test session often required more than one practitioner. For both VEP and ERG, more than 70% of respondents required at least 30 min for each test. The majority indicated that they followed the ISCEV standards for stimuli and data acquisition. Almost all (94%) reported using the ISCEV recommended VEP electrode configuration. For ERG, most (88%) used ocular contact electrodes (including contact lens, thread, foil and HK loop), but 12% used skin electrodes exclusively and some (17%) used skin electrodes at times. CONCLUSIONS: Pediatric ERG and VEP testing is a labor intensive endeavor of highly trained professionals. ISCEV technical standards are typically met or exceeded, indicating that high quality testing of infants and children is feasible. Revision of the ISCEV ERG standard is necessary to bring actual practice into accord with evidence-based recommendations for infant testing.

Child↗

PubMed2006

ON- and OFF-response of the photopic electroretinogram in relation to stimulus characteristics.

The aim of this study was to explore the effect of stimulus duration, stimulus intensity, stimulus wavelength and background luminance on the amplitude and waveform of the ON- (b-wave) and OFF- (d-wave) response of the photopic ERG. The following parameters were used in this study: stimulus duration from 5 to 200 ms, the flash intensities from 0.4 to 2.1 log cd s/m2, the background luminance from 20 to 50 cd/m2 and stimulus wavelengths 460, 508 and 667 nm. Prolonging the stimulus duration from 75 to 200 ms did not influence the amplitudes of a-, b- and d-waves significantly. Higher stimulus intensities (1.9 log cd s/m2) broadened the b-wave and increased variability of its implicit time. With a brighter background (50 cd/m2) the b-wave did not broaden and its optimal amplitude was preserved. Stimuli of longer wavelengths (667 nm) significantly reduced the d-wave amplitude. Our results suggest that high intensities and longer wavelengths (red) may not be suitable stimulus parameters in the routine clinical ON- and OFF-response recording.

Adult↗

PubMed2004

Visual electrophysiological screening in diagnosing infants with congenital nystagmus.

OBJECTIVE: To determine the value of visual electrophysiological screening in evaluating retinal and postretinal visual pathway function in infants with congenital nystagmus. METHODS: In 28 infants with congenital nystagmus electroretinogram (ERG) was recorded with skin electrodes and, since the infants were alert, visual evoked potentials (VEP) were simultaneously recorded. The first recording was performed before the age of 1 year (age 2-11 months, mean age 6.8 months). Follow-up was performed between the ages of 7 months and 6 years (mean age 2.7 years). ERG was detected to flash stimulus and VEP to flash and/or pattern-reversal stimulus. RESULTS: In infants less than 1 year of age, retinal dysfunction was recognised in 36% of infants who had been diagnosed as Leber's congenital amaurosis, achromatopsia and retinal dystrophy; postretinal dysfunction was recognised in 32% of infants who had been diagnosed with ocular albinism, optic nerve hypoplasia and neurological nystagmus; retinal or postretinal function was normal in 7% of infants that had been diagnosed as congenital idiopathic nystagmus, while retinal function was normal and postretinal function was undefined in 25% of infants that had been diagnosed as optic nerve hypoplasia, neurological nystagmus and congenital idiopathic nystagmus. At follow-up the findings were: retinal dysfunction in 36%, postretinal dysfunction in 50% and normal retinal and postretinal function in 14% of children. All those children with normal retinal and postretinal function had been diagnosed as congenital idiopathic nystagmus. CONCLUSIONS: Visual electrophysiological screening of infants with congenital nystagmus can establish or exclude retinal and postretinal pathway dysfunction. Therefore simultaneous skin ERG and VEP which is a non-invasive approach for infants enables an objective means for identifying the basis of congenital nystagmus, thereby assisting in its classification.

Child↗

PubMed2004

Visual evoked potentials in multiple sclerosis patients treated with interferon beta-1a.

AIM: To study pattern-reversal visual evoked potentials (VEP) in patients with relapsing-remitting multiple sclerosis on interferon beta-1a treatment. METHODS: In a randomized, prospective, non-blinded, placebo-uncontrolled study, VEP were studied in 9 patients (18 eyes) with relapsing-remitting multiple sclerosis treated with interferon. Three of them have had an episode of unilateral optic neuritis. VEP were first recorded before interferon treatment and then followed up for 12 months, at 3-month intervals, in the time when patients were receiving interferon, 11 microg twice weekly. All patients did not appear regularly at 3-months intervals follow-up, except for 6-month follow-up. P100 latency and P100 amplitude in responses to full field, right and left half-field stimulation were evaluated. RESULTS: For the group of 18 eyes, there was no statistically significant difference in P100 latency and P100 amplitude before and after 6 months of treatment. In individual cases P100 latency was delayed in 3 eyes of 3 patients with a history of optic neuritis before treatment. At follow-up, P100 latency remained delayed in 3 eyes with a history of optic neuritis. Further, in 3 eyes of two patients who have had normal P100 latency before treatment, P100 latency became delayed. Overall, P100 latency was at follow-up delayed in 6 eyes of 5 patients. CONCLUSION: Interferon beta-1a therapy (22 microg per week) administered for 12 months during 1998/99 in Croatia showed no statistically significant VEP changes in the group of relapsing-remitting multiple sclerosis patients. However, VEP may reveal evidence for asymptomatic deterioration.

Adult↗

PubMed2003

From immature to mature pattern ERG and VEP.

Electrophysiological parameters in children reflect not only pathological processes, but also maturation of the visual system. This review investigates PERG and PVEP changes in infants and schoolchildren in order to establish the time scale for electrophysiological maturation of the visual system. Studies using pattern-reversal and pattern-onset stimulation are presented. Maturational changes have been found to be rapid in infants and gradual in schoolchildren. PERG age-related changes in infants were seen as a decrease in latency and in schoolchildren as a decrease in amplitude. PVEP age-related changes in infants were seen as a decrease in latency, an increase in amplitude and the development of the waveform. In schoolchildren, PVEP changes were more gradual, with a decrease in latency, a decrease in amplitude and transformation of the waveform. In conclusion, electrophysiological maturation proceeds until adulthood. Therefore, in paediatric clinical work, normative values in infants and schoolchildren are an important factor in differentiating maturation of the visual system from pathological processes.

Adolescent↗

PubMed2002

Pattern ERG and VEP maturation in schoolchildren.

OBJECTIVE: The maturation of the visual system has been studied with pattern electroretinograms (PERG) and pattern visual evoked potentials (PVEP) mostly in children under the age of 6 years. To address the question of maturation of the visual system in childhood and adolescence we investigated age-dependent PERG and PVEP changes in children aged 7-18 years. METHODS: PERG were recorded with skin electrodes attached to the lower eyelid, and PVEP were recorded with 5 electrodes. Visual stimuli, consisting of pattern-reversal 50' checks to full-field and to half-field stimulation, were applied to obtain macular (N70, P100, N145) and paramacular waves (P80, N105, N135). RESULTS: We found an age-dependent decrease (linear regression P<0.05) of PERG P50 amplitude and full-field PVEP P100 latency to monocular right and left eye stimulation, indicating central retinal and postretinal changes. In addition, waveform changes were found in responses to half-field stimulation. The paramacular wave N105 was typically enhanced in younger schoolchildren and diminished with age. The age-dependent decrease (linear regression P<0.01) of paramacular N105 amplitude indicated the increasing predominance of the macular structures of the visual system. CONCLUSIONS: Our findings suggest that central retinal and postretinal electrophysiological maturation persists throughout childhood. Age-dependent PVEP changes seem to correlate with the morphological and metabolic findings that maturation of the visual cortex continues until puberty and even later.

Adolescent↗

PubMedDate not supplied

Visual evoked potentials to red-green stimulation in schoolchildren.

The aim is to study chromatic visual evoked potentials (VEP) to isoluminant red-green (R-G) stimulus in schoolchildren. Sixty children (7-19 years) with normal color vision were examined, 30 binocularly and 30 monocularly. The isoluminant point was determined for each child subjectively by using heterochromatic flicker photometry, and objectively from recordings. The stimulus was a 7 degrees circle composed of horizontal sinusoidal gratings, with spatial frequency 2 cycles/degrees and 90% contrast, presented in onset-offset mode. VEP were recorded from Oz (mid-occipital) position. Age-dependent waveform changes and changes of the positive and negative wave were studied to both binocular and monocular R-G stimulation. Age-dependent waveform changes were observed to binocular and monocular R-G stimulation. In younger children the positive wave was prominent, whereas in older children also the negative wave became more evident. The latency of the positive wave decreased linearly with age to R-G binocular stimulation. To monocular stimulation no significant changes of the latency were observed. The amplitude of the positive wave dropped exponentially with age to binocular and monocular stimulation. The latency of the negative wave increased linearly with age to binocular and monocular stimulation, whereas the amplitude did not show age-dependent changes. These findings suggest that the chromatic VEP response undergoes evident age-dependent changes during the school-age period.

Adolescent↗