Pattern Visual Evoked Potentials Research Articles

Acute effects of cigarette smoking on multifocal electroretinogram

Cigarette smoking was shown to have stimulant effects on pattern visual-evoked potentials. The aim of this study was to investigate the acute effects of cigarette smoking on multifocal electroretinogram (mfERG). This prospective case-control study was held in a tertiary referral centre in Turkish Armed Forces. mfERGs were investigated in a group of habitual smokers (30 right eyes of 30 subjects) in separate real smoking and sham smoking sessions. mfERG responses of the subjects were recorded after overnight abstinence. The responses were averaged over five retinal regions, the central hexagon (CH; central 6 degrees) and four concentric rings (ring 1 [R1; 7-12 degrees], ring 2 [R2; 13-18 degrees], ring 3 [R3; 19-24 degrees], ring 4 [R4; 25-30 degrees]). On each session mfERGs were recorded before (BS) and after smoking (AS) conditions. Regarding P1 amplitudes (first positive deflection of the mfERG) in the real smoking sessions, the differences were significant in the CH (BS: 66.2 +/- 16.3 microV, AS: 73.3 +/- 19.6 microV, P < 0.001), in R1 (BS: 44.3 +/- 13.0, AS: 48.3 +/- 16.0, P = 0.004) and in R2 (BS: 30.1 +/- 8.3, AS: 33.7 +/- 9.7, P = 0.002). Similar results were found for N1 amplitudes and P1 and N1 (first negative deflection of the mfERG) latencies in the CH, R1 and R2. The differences in outer retinal areas (R3, R4) in the real smoking sessions and in all rings in the sham smoking sessions were not significant. Cigarette smoking may stimulate the central retinal areas in the acute phase. This effect may be related with the stimulant effect of nicotine on neurotransmission, deleterious effects on retinal and/or choroidal circulation, carbon monoxide toxicity and nicotine withdrawal.

Early effects of sodium iodate injection on pattern VEP of rabbits

目的 观察静脉注入碘酸钠后早期引起的兔眼图形视诱发电位(P-VEP)的改变,从而推测出视力的变化.方法 将10 mg/ml碘酸钠40 mg/kg从兔耳缘静脉注入体内.镜片矫正兔眼屈光不正,注药前及注药后3 h分别对兔右眼P-VEP进行检测(翻转棋盘格,分别对应的视角6'、3'、1.5').结果 注药后3 h,光感受器细胞未见明显损害,3 d后,外节中可以看到许多空泡样改变.注药前约50 ms可记录到一个正向的反应波(P100),注药后3 h此波明显下降或消失(配对t检验,P＜0.05).结论 静脉注入碘酸钠后3 h可以影响兔眼视力。

Measurement of autofluorescence in the parapapillary atrophic zone in patients with ocular hypertension

The purpose of the study was to investigate area and intensity of parapapillary autofluorescence in patients with ocular hypertension and controls. Forty-two consecutive patients with ocular hypertension and 25 controls were investigated in a controlled prospective cross-sectional trial. All patients and controls were members of the Erlangen Glaucoma registry and received complete ophthalmologic examination and detailed standardized glaucoma examination, including 24-h IOP measurement, perimetrie (G1, three phases) and 15 degrees stereographic slides of the optic disc. Additionally, patients and controls were investigated with VEP with blue on yellow pattern stimulation and confocal scanning laser ophthalmoscope (HRA II, Heidelberg Engineering, Dossenheim, Germany) to detect lipofuscin in the parapapillary atrophic zone. Eyes with retinal diseases or pathologic changes of retinal pigmentepithelium were excluded. Extension of parapapillary area with increased autofluorescence compared (qualitatively) to background autofluorescence around the optic disc and the level of autofluorescence (quantitatively) in the area of qualitatively increased autofluorescence was measured. Patients and controls did not differ significantly concerning age. The area of parapapillary autofluorescence was significant larger in patients with ocular hypertension than in the control group (0.21+/-0.17 mm(2) versus 0.07+/-0.06 mm(2); P<0.001, Mann-Whitney U-test). An increased latency of blue-on-yellow pattern VEP was seen in patients with OHT with increasing parapapillary autofluorescence area (r=0.496; P<0.001, Spearman-Rho test). Parapapillary autofluorescence is increased in patients with ocular hypertension. Patients with large area of parapapillary autofluorescence had also an increased latency in blue on yellow pattern VEP.

Comparison of Pattern Visual-Evoked Potentials to Perimetry in the Detection of Visual Loss In Children With Optic Pathway Gliomas

We sought to compare visual evoked potentials (VEPs) with standard visual field testing in children with visual pathway gliomas. Fifteen of 40 children with visual pathway gliomas verified on magnetic resonance imaging scan who cooperated with Goldmann visual field (GVF) and 3-channel VEPs were studied. GVFs were obtained in 25 eyes with adequate vision. VEP amplitudes, latencies, and signal-to-noise ratios (SNRs) were compared with control subjects. Four of the patients (5 eyes) also had Humphrey visual field testing. Twenty-two of 25 eyes had a field defect, 15 eyes showed a relative or absolute hemianopia, 7 eyes showed a central or generalized depression, and 3 eyes were normal. In hemianopic eyes, 87% showed a depression (GVF) or reduced sensitivity (Humphrey field) in the opposite hemifield. VEP amplitudes and SNRs, normally largest at the midline electrode, were significantly reduced in all eyes with visual field loss. By comparison, lateral electrodes showed significantly lower amplitudes and SNRs in patients and controls. Interhemispheric VEP asymmetry (>2:1 ratio) was seen in 67% of patients with hemianopia and 53% of controls. Reduction of amplitude and SNR at the midline VEP electrode was a sensitive indicator of visual field loss. Interhemispheric VEP asymmetry was not reliable in detection of a hemianopic field defect. VEPs can be a reliable and objective alternative for the detection of visual loss due to optic pathway glioma in children who are intolerant to visual field testing. We recommend the test protocol include pattern-onset and check reversal stimuli of at least one high and one low spatial frequency.

Functional assessment of reattached macula in nine cases with excellent Snellen acuities

To compare the macular functions of patients with excellent visual acuity after retinal detachment (RD) surgery, with the healthy fellow eye. Of 214 patients, nine patients, who were successfully operated because of unilateral RD involving the macula and achieved excellent visual acuity, were analysed. The fellow eyes of the patients were taken as the control group. The macular functions were evaluated with visual acuity, contrast sensitivity, colour vision, visual field, and pattern VEP in operated and nonoperated eyes. There was no significant difference in visual acuity, contrast sensitivity, colour vision, and VEP outcomes between operated and nonoperated eyes. However, it was seen that the mean deviation in the visual field was significantly higher in the operated eyes (5.8+/-1.8 dB) when compared with the undetached fellow eyes (3.1+/-1.8 dB), (t=12.5; P=0.013). Even though the visual acuity, colour vision, contrast sensitivity, and VEP results returned to normal after a successful RD surgery, we found that the mean deviation measured by the visual field, which reflects the retinal sensitivity, was still significantly low after nearly 5 years follow-up.

Clinical Ability of Pattern Electroretinograms and Visual Evoked Potentials in Detecting Visual Dysfunction in Ocular Hypertension and Glaucoma

To assess the presence of normal or abnormal pattern electroretinogram (PERG) and visual evoked potential (VEP) responses in patients with ocular hypertension or open-angle glaucoma (OAG). Retrospective, cross-sectional, case-control study. Eighty normal control subjects (mean age, 51.77+/-6.04 years; 80 eyes), 68 ocular hypertension patients (mean age, 51.58+/-7.12; 68 eyes; intraocular pressure [IOP] < 18 mmHg under pharmacological treatment; Humphrey field analysis [HFA] 24/2 mean deviation [MD] > -2 decibels [dB]), and 84 OAG patients (mean age, 52.77+/-5.28; 84 eyes; IOP < 18 mmHg under pharmacological treatment; HFA 24/2 mean deviation between -2 and -23 dB) were enrolled. Simultaneous recording of PERGs and VEPs using high-contrast (80%) 15' checkerboard stimuli reversed at the rate of 2 reversals per second. Pattern electroretinogram P50 and VEP P100 implicit times were considered delayed when exceeding the limit of mean values of controls plus 2 standard deviations (SDs). Pattern electroretinogram P50 to N95 and VEP N75 to P100 amplitudes were considered reduced when exceeding the limit of mean values of controls minus 2 SDs. Pattern electroretinogram: P50 implicit times were delayed in 58 of 68 (85.30%) ocular hypertension eyes and 83 of 84 (98.80%) OAG eyes; P50 to N95 amplitudes were reduced in 47 (69.12%) ocular hypertension eyes and 84 (100%) OAG eyes. Visual evoked potential: P100 implicit times were delayed in 58 (85.30%) ocular hypertension eyes and 84 (100%) OAG eyes; reduced N75 to P100 amplitudes were observed in 39 (57.35%) ocular hypertension eyes and 73 (86.90%) OAG eyes. Ocular hypertension eyes showed no significant correlations (Pearson test, P>0.01) between electrophysiological parameters and age, IOP before or under medical treatment, HFA, and corneal thickness values. Significant correlations (P<0.01) were observed in OAG eyes between electrophysiological results and HFA values. Pattern electroretinogram and VEP responses were normal in all control eyes. Combined PERG/VEP recordings identified a large percentage of ocular hypertension eyes with impairment of the innermost retinal layers, notwithstanding normal optic disc morphology and normal HFA. In OAG eyes, PERG P50 to N95 amplitude and VEP P100 implicit time showed the highest sensitivity/specificity for the detection of a visual dysfunction. The presence of abnormal PERG and/or VEP responses did not allow a clearcut separation between ocular hypertension and OAG eyes.

Pattern Reversal ERG and VEP – Comparison of Stimulation by LED, Monitor and a Maxwellian-view System

Pattern stimulation is widely used to detect inner retinal dysfunction. In this work we describe a pattern stimulation technique with LEDs and compare the results with conventional methods. PERG and VEP were derived from three normal subjects. Three different techniques were used to generate a checkerboard pattern reversal stimulus: a 70 Hz monitor, a Maxwellian-view system equipped with a Xenon-arc lamp and a mechanical mirror system, and a LED array (Roland Consult) consisting of 100 white LEDs. Two kinds of luminance (125 and 340 cd/m2) and four temporal frequencies (4, 8, 12 and 24 reversals per second) were studied on three healthy subjects. Additionally, a luminance tuning experiment (30, 60, 90, 125 and 340 cd/m2) was performed on one subject. Comparison of different stimulation techniques shows reproducible responses of PERG and VEP with all three methods. The LED array leads to slightly smaller amplitudes than both other techniques, which we ascribe to the design of the LED field. No difference of peak times or phases was noticed between different stimulation techniques. A luminance dependency of PERG and VEP is noticeable using stimulation with LED: with decreasing luminance we measured increasing peak times of PERG and VEP and decreasing amplitude of PERG. We conclude that central retinal stimulation with checkerboard pattern reversal is possible with LED. It gives comparable results to monitor and Maxwellian-view system.

Conventional Perimetry, Short-Wavelength Automated Perimetry, Frequency-Doubling Technology, and Visual Evoked Potentials in the Assessment of Patients with Multiple Sclerosis

To evaluate the diagnostic power of conventional, achromatic, automated perimetry (CAP), short-wavelength automated perimetry (SWAP), frequency-doubling technology (FDT) perimetry, and visual evoked potentials (VEP) in a group of patients with multiple sclerosis (MS) with or without a history of optic neuritis. Thirty eyes of 15 patients (5 male, 10 female, average age 38+/-7 years) with confirmed diagnosis of MS underwent CAP, SWAP (Humphrey 750-II VFA, program central 30-2, full-threshold strategy), FDT perimetry (program N-30), and pattern VEPs. Sixteen eyes (53.3%) had no history of ocular involvement and a negative ophthalmologic examination. They were matched with a control group of 10 healthy volunteers (4 male, 6 female, average age 31+/-10 years). The mean deviation (MD) and the pattern standard deviation (PSD) of the two groups were compared (t-test). Fourteen eyes (46.7%) had, on the contrary, a history of optic neuritis. Inside this group, the MD and the PSD of the three techniques were correlated (Spearman's rank test), in order to investigate whether any significant differences might be revealed by these techniques in pointing out the total amount of visual field damage. When comparing MS patients without signs or symptoms of ocular involvement and a control group, no significant differences were found for CAP MD, CAP PSD, and FDT PSD. Significant differences were found, on the contrary, for SWAP MD (p=0.0014), SWAP PSD (p=0.0001), and FDT MD (p=0.0001). When considering the MD and the PSD of the three techniques in the group of MS patients who had a history of optic neuritis, a significant correlation was found only between CAP MD and SWAP MD (r=0.0057), with a tendency by SWAP to reveal a higher rate of visual field loss. The other correlations were not significant. According to predefined criteria, the group of asymptomatic subjects had abnormal CAP in 1 eye (6.25%), abnormal SWAP in 9 (56.2%), abnormal FDT in 11 (68.7%), and abnormal VEPs in 7 (43.7%). The combined use of all techniques allowed us to identify silent optic nerve impairment in 15 (93.7%) eyes. Short-wavelength automated perimetry and FDT perimetry are two non-conventional perimetric techniques that were mainly developed for the early detection of glaucomatous damage. The results of this study demonstrate their efficacy also in detecting early visual field deficits in MS patients without clinical signs of optic neuropathy. Frequency doubling perimetry, in particular, proved to be an easy, fast, and sensitive technique in the assessment of patients with MS. Our results also suggest that subclinical visual involvement in MS can be better diagnosed using multiple (neurophysiologic and psychophysical) tests.

Identification of XLRS1 Gene Mutation (608C&gt;T) in a Portuguese Family with Juvenile Retinoschisis

To characterize electroretinogram (ERG) and molecular genetic findings in a family with XLRS1 mutation. The authors present two cases of a Portuguese family with juvenile retinoschisis with a mutation in exon 6. Two brothers and their parents, grandmother, and uncle underwent a full ophthalmic examination. The two brothers with ophthalmic disease were evaluated with color fundus photography, fluorescein angiography, optical coherence tomography (OCT), molecular genetic study (Group VI of Retinoschisis Consortium), pattern visual evoked potential (PVEP), and full field ERG. Both patients presented funduscopic manifestations of vitre o retinal degeneration. They presented peripheral schisis and retinal detachment. However, foveal schisis had never been observed at funduscopy. A negative ERG was recorded in both. Six months after that, the younger brother showed a typical foveal schisis at fundus examination. A retinoschisis gene (XLRS1) mutation with transition of cytosine by thymine at position 608 (608C > T) had been identified in both. Negative ERG is the most secure clinical marker to establish the diagnosis of juvenile retinoschisis. XLRS1 gene 608C > T mutation was described for the first time in a Portuguese family.

The Value of Visual Evoked Potentials in the Evaluation of Periorbital Hemangiomas

To present a case of a child with an extensive facial hemangioma in whom the suspicion of intracranial involvement was raised by visual evoked potential (VEP) evaluation. Observational case report. VEP analysis was performed using flash and pattern stimuli to determine whether treatment intervention other than occlusion therapy was needed. VEP analysis indicated a marked transoccipital asymmetry in the flash and pattern VEP suggestive of right hemispheric dysfunction. Neuroimaging showed intracranial extension of the hemangioma. The VEP evaluation is a noninvasive technique performed in the awake child. This case highlights the usefulness of VEP analysis in the management of extensive periocular capillary hemangiomas and its use as a modality to identify potential intracranial involvement. Large plaquelike facial capillary hemangiomas may have possible underlying dural involvement suggestive of PHACES syndrome.

Pattern Visual Evoked Potentials in Eyes with Disc Swelling due to Cat Scratch Disease-associated Neuroretinitis

To evaluate optic nerve function by pattern visual evoked potentials (VEPs) in eyes with optic disc swelling due to neuroretinitis associated with cat scratch disease (CSD). Four eyes of four patients with marked optic disc swelling resembling optic neuritis but diagnosed serologically as CSD received systemic steroid treatment. VEPs elicited by black and white checkerboard stimuli created on a TV monitor were recorded before the treatment. The visual acuity (VA) in the affected eyes was decreased to 20/50 in two eyes and finger counting in two eyes at their initial visits. Ophthalmoscopic examination revealed neuroretinitis characterized by severe optic disc swelling, chorioretinal exudates, and macular edema in all eyes. Anti-Bartonella henselae serum antibody was markedly elevated in all patients confirming the diagnosis of CSD. The P100 of the transient VEPs was only mildly reduced without a delay in the implicit times in three eyes and only slightly delayed in the other eye. The steady-state VEPs were mildly reduced in two eyes and phase-reversed in other two eyes. The VA fully recovered after systemic steroid treatment in all patients. Although all examined patients showed marked swelling of the optic disc and visual decrease, the pattern VEPs were not affected as severely as in idiopathic optic neuritis. However, the degree of change of the pattern VEPs varied among patients.

Visual electrophysiological evaluation in paclitaxel-treated patients. Pathophysiological mechanisms involved in retinal and optic nerve dysfunctions

We studied 30 breast cancer patients to clarify the underlying pathophysiological mechanisms of visual pathway involvement during paclitaxel treatment. Pattern visual-evoked potentials (VEPs) and transient, 30 Hz flicker (FLK) and oscillatory potential (OP) white flash electroretinograms (ERG) were performed before treatment, after the third and sixth cycles, and at the end of treatment. Abnormal pretreatment VEP and OP and FLK changes were observed in respectively about 75% and just under 50% of the patients; transient ERG was normal in over 90%. Serial recordings: VEP unchanged; ERG b-wave latency increased at the end of therapy; OP and FLK mildly attenuated. Various combinations of ERG, OP, FLK and VEP changes occurred in 50%, and poorly correlated with the visual symptoms reported by 12 patients. A few patients had stable and persistent subclinical electrophysiological changes. The high incidence of pretreatment, subclinical electrophysiological abnormalities correlated with the administration of tamoxifen and/or other chemotherapeutic drugs most of the patients had been taking before starting paclitaxel. On the basis of our findings, we suggest that the more likely mechanism of visual symptoms and electrophysiological changes during paclitaxel administration is vascular dysregulation in the retina or ischemic mechanisms when the optic nerve is involved.

Pattern VEP Alterations in Psoriatic Patients may Indicate a Sub Clinic Optic Neuritis

We examined 44 subject (Group A) of both sexes (27 males and 17 females) aging between 16 and 80 (average: 45+/-16.6), divided into age bands, affected by mild-medium psoriasis with PASI (psoriasis area and severity index) between 1.2 and 48.6 (average: 11.2+/-9.7) without any other disease and we performed pattern transient VEP (Visual Evoked Potential) at the frequencies usually used in clinical experience (73', 36', 18' check size). For a good statistic comparison we choose 55 healthy subjects (group B) divided into age bands on which we performed the same test. Comparison of VEP parameters between psoriatic and healthy subjects, showed in group A 10 normal (22.7%) and 34 pathological (77.3%). In the latter group there are 16 subjects who show only a P100 reduced amplitude (36.3%), 3 with only increased latency (6.8%), 15 with alterations of both values (34%). The achieved data show that more than 3/4 of group A subjects have VEP alterations as index of the presence of a sub clinic optic neuritis with a probably toxic autoimmune origin due to the action of TNFalpha, of IgG, of ECP or of other cytokines (IL6, IL7, etc) that are increased in the blood of this patients. The electro physiologic monitoring of optic nerve seems to represent a good routine test to evaluate the global conditions of psoriatic patients.

Effects of flash mode and intensity on P2 component latency and amplitude

Alzheimer's disease (AD) groups manifest flash visual-evoked potential (VEP) P2 component delays compared to healthy control groups. However, using P2 latency to categorize individual patients and controls yields low accuracy. Additionally, several laboratories have failed to replicate the basic between group P2 latency findings. The sporadic failure to find the P2 delay and, when found, its failure to classify patients and controls accurately may reflect the use of non-optimal stimuli or recording sites. Objective This was a parametric investigation of stimulation and recording methods in healthy college students. Method Using an extended recording montage of 64 electrodes, 10 stimulus conditions (5 flash intensities through open and closed eyes) were evaluated for their P2 effects. Result The optimal recording site (O2) yielded the most reliable latencies and amplitudes across a range of stimulus intensities. Flash intensity did not affect P2 latency or amplitude. Flashes delivered through closed eyelids produced a flash VEP but delivery through open eyes produced a pattern VEP lacking a flash P2 component. Conclusion This accounts for the failure of some laboratories using open eyes to replicate the P2 delay in AD groups. Significance Optimal flash VEP conditions include closed eyes and recording from O2. Flash intensity is unimportant.

Effect of defocusing and of distracted attention upon recordings of the visual evoked potential

Pattern reversal visual stimuli are used to evoke potentials (VEPs) for assessment of visual acuity and for localizing defects along the visual pathways. Our goal was to assess the importance of attention and defocusing to the recordings of pattern VEP. Forty-one volunteers with normal (6/6) corrected visual acuity participated in this study. Twenty-one were asked to defocus intentionally the visual stimulus (located 200 cm away) by fixating at a target 25 or 50 cm from the eye. Twenty other subjects performed auditory tasks to distract their attention from the visual stimulus. Pattern VEPs were elicited by different check sizes. The amplitude and time-to-peak of the P100 wave were measured. Intentional defocusing caused amplitude reduction and prolongation of the time-to-peak in young subjects (20-34 years old). With the smallest checks used (7.5') we could not record a reliable response from 43% of the young subjects (6 out of 14). In older patients (35-61 years old), intentional defocusing induced negligible effects on pattern VEPs regardless of check size. There were no effects of auditory distraction upon the pattern VEPs. Our data suggest that intentional defocusing can produce false positive results (reduced VEP with prolonged time-to-peak) only when small checks are used in young subjects. Divided attention has negligible effect on the recordings of pattern VEPs. With proper controls, the pattern VEP test can be used for objective assessment of visual function.

Pattern VEP is a useful technique in monitoring the effectiveness of occlusion therapy in amblyopic eyes under occlusion therapy

To evaluate the effectiveness and clinical significance of pattern visual evoked potential (P-VEP) parameters on visual acuity in amblyopic patients under occlusion therapy. A total of 34 consecutive children with anisometropic amblyopia were included in this study. All patients underwent a full initial ophthalmologic and orthoptic evaluation. P-VEP test was performed in all cases and binocular vision was tested and recorded with Worth's four-dot test and Bagolini striated glasses at each visit. Part-time occlusion therapy was performed by using adhesive patches. The mean (+/- SEM) cycloplegic refractive error was + 5.6 +/- 0.6 diopters (D) in the amblyopic eyes and + 1.8 +/- 0.2 D in the normal eye. The mean levels of best-corrected visual acuity were statistically differed between each measurement for occlusion therapy (for each, p < 0.05). The ratio of the patients with binocular vision increased after 6 months occlusion therapy and the difference was statistically significant (p < 0.05). In addition, P100 amplitude improved at each visit and the difference was significant when compared with baseline values (for each, p < 0.05). P100 amplitude of the P-VEP test parallels the improvement in subjective visual acuity in amblyopic eyes under occlusion therapy. Therefore, this test may be useful in monitoring the visual acuity in the preverbal or non-verbal patched patients.

Amiodarone and optic neuropathy.

To investigate the clinical, perimetric, contrast sensitivity and visual evoked potentials findings in patients on longterm treatment with amiodarone. We enrolled 14 patients (age range 47-78 years, mean age 62.7 years) on chronic amiodarone therapy (mean cumulative dose of 519 g), and 14 age-matched control subjects. Participants were submitted to ophthalmological examination, kinetic visual field testing (Goldmann), standard achromatic automated perimetry (central 30-2, Humphrey), computerized isoluminant chromatic contrast sensitivity (CCS) and pattern visual evoked potentials evaluation (VEP). Data from baseline, 6-month and 1-year follow-up examinations were analysed. The main outcome measures were: initial and final corrected visual acuity; corneal, optic disc and fundus abnormalities; mean deviation (MD) and pattern standard deviation (PSD) central 30-2 perimetry parameters; visual field loss on kinetic perimetry; indices of CCS (tritan, protan and deutan axes), and pattern VEP latency (L-VEP) and VEP amplitude (a-VEP). We found a statistically significant difference between the patients and controls' baseline L-VEP and a-VEP measurements (p < 0.001). We found no significant correlation between prolonged L-VEP and duration of amiodarone use (r = 0.07). After a 1-year follow-up, we evidenced an average increment in L-VEP of 1.96 ms and a-VEP measurements showed a decline of 0.69 micro V. In cumulative dose-specific analyses, mean differences between baseline and 12-month L-VEP measurements were more evident in those taking higher than 200 g cumulative amiodarone doses (p = 0.03). We found abnormal tritan CCS results in 19 eyes (68%). Of these, four eyes belonged to patients with no ocular disease (diabetes, cataracts). No significant differences were observed between the baseline and 12-month clinical eye examinations, central 30-2 perimetry and CCS results. We found a significant prolongation in pattern L-VEP and a significant reduction in pattern a-VEP in patients on longterm treatment with amiodarone compared to control subjects. Nevertheless, current data are insufficient to recommend appropriate methods of visual screening.

Magnocellular and parvocellular developmental course in infants during the first year of life.

The visual system undergoes major modifications during the first year of life. We wanted to examine whether the magnocellular (M) and parvocellular (P) pathways mature at the same rate or if they follow a different developmental course. A previous study carried out in our laboratory had shown that the N1 and P1 components of pattern visual evoked potentials (PVEPs) were preferentially related to the activity of P and M pathways, respectively. In the present study, PVEPs were recorded at Oz in 33 infants aged between 0 and 52 weeks, in response to two spatial frequencies (0.5 and 2.5 c deg(-1)) presented at four contrast levels (4, 12, 28 and 95%). Results indicate that the P1 component appeared before the N1 component in the periods tested and was unambiguously present at birth. The P1 component showed a rapid gain in amplitude in the following months, to reach a ceiling around 4-6 months. Conversely, the N1 component always appeared later and then gained in amplitude until the end of the first year without reaching a plateau. Latencies were also computed but no developmental dissociation was revealed. Results obtained on amplitude are interpreted as demonstrating a developmental dissociation between the underlying M and P pathways, suggesting that the former is functional earlier and matures faster than the latter during the first year of life.

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.

Influence of the state of alertness on the pattern visual evoked potentials (PVEP) in very young infant

The aim of the study was to evaluate the pattern visual evoked potentials (PVEP) combined with an optimal state of vigilance, called liberated state (LS), in order to improve testing in very young infants. Transient PVEP were recorded in response to a checkerboard pattern of 120, 60 and 30 min of arc. in 56 fullterm newborns and 79 preterm infants from birth to 4 months of age. In the fullterms, 28 infants in each group were tested in LS or spontaneous alertness (SA) while in the preterms, 48 infants in each group were tested in LS or SA. No significant difference was found in the amplitude and/or peak time of the PVEP responses between subjects tested in LS compared to SA groups. However, the LS condition improved by approximately 25% the feasibility of prolonged PVEP testing in preterms aged less than 2 months (corrected age). This suggest that the LS condition enhances the clinical feasibility of PVEP testing in very young infants and should be used to optimize the evaluation of visual development in high risk infants in this age group.