Normal Visual Evoked Potentials Research Articles

Role of visual evoked potential (VEP) in indirect traumatic optic nerve (ITON) injuries and assessment of the visual outcome

To demonstrate the critical function of Visually Evoked Potential (VEP) in the prompt detection of indirect optic neuropathy. 60 patients suspected of having traumatic optic nerve injury underwent VEP testing in < eight hours of traumatic experience. Baseline visual acuity was revealed to be the most imperative prognosticator of eventual visual outcome. The VEP was instrumental in the primary detection as well as validation of ITON. Additionally, VEP aided in predicting prognosis and follow-up for patients with IITON. Visual recovery is impossible in the absence of recordable VEP waves. The manifestation of orbital fractures wasn't associated with a preliminary or ultimate visual perception decrease. Patients who present < 8 hours following ITON with normal initial visual acuity, VEP alterations, and lower RAPD grades may have a greater chance of recovering final visual perception when treated with an instantaneous high steroid dosage. The above-mentioned prognostic markers in patients with ITON may be beneficial in predicting visual prognosis and determining the need for surgical therapy in patients who experience vision loss following head trauma.

Evaluation of visual evoked potential in chronic myeloid leukemias.

Visual complaint is not very uncommon in chronic myeloid leukemia (CML) patients. Our study aims to evaluate the visual pathway using visual evoked potential (VEP) in cases of CML at the time of diagnosis and 6 weeks after tyrosine kinase therapy, to find out treatment impact in asymptomatic as well as symptomatic individuals and compare it with the general population. This is an analytical cross-sectional study. The study group comprised 20 newly diagnosed cases of CML and 20 age- and sex-matched healthy control population. A thorough history and clinical examination with detailed ophthalmological studies, including VEP, were done. Cases who had VEP abnormalities were then followed-up after 6 weeks post-Imatinib therapy and underwent repeat investigations, including VEP. VEP in cases was significantly deranged (P < 0.001), where 15 patients (75%) had abnormalities in VEP compared to 3 (15%) in control. Post 6 weeks chemotherapy, Out of 10 cases that were followed up, 7 patients had achieved hematological remission with normal VEP finding (P = 0.02). Simultaneously, an increase in hemoglobin (P = 0.002) and reduction in total leukocyte count (TLC) (P = 0.004) were observed. Considerable evidence appear to support the notion that CML patients have a higher prevalence of ophthalmic manifestations as compared to the general population, which can be screened earlier with objective tests like VEP. Concurrently, hematological parameters and VEP showed derangement at the time of diagnosis. After 6 weeks of Imatinib treatment, the improvement in VEP can then be attributed to a reduction in TLC. Hence it can be deduced that VEP has paramount importance in the early identification of ophthalmic manifestations, which are reversible with timely treatment.

VEP Score of a Left Eye Had Predictive Values for Achieving NEDA-3 over Ten Years in Patients with Multiple Sclerosis.

The aim of this study was to determine the predictive value of visual evoked potentials (VEPs) in patients with relapsing-remitting multiple sclerosis (RRMS) in achieving no evidence of disease activity-3 (NEDA-3) during up to 10 years of first-line immunomodulatory therapy and to determine whether the lateralization of optic nerve damage may have prognostic significance concerning clinical disability and response to therapy. In a retrospective study, a total of 83 patients (53 female and 30 male) with RRMS participated. The average age of patients was 38.31 ± 9.01. Patients were followed for 2, 5 or 10 years. VEPs were measured at the beginning of the follow-up and after many years of monitoring. Data on optical neuritis (ON) were obtained from medical history. The degree of disability was estimated by the neurologist (independent rater), and magnetic resonance (MR) imaging of the endocranium was performed with gadolinium contrasts. Achieving NEDA-3 is considered a favorable outcome of treatments. Among those treated, 19 (22.9%) reached NEDA-3, while 64 (77.1%) did not reach NEDA-3. The values of the evoked potential (EP) score for the left eye (r = 0.008, odds ratio (OR) = 0.344 (0.156-0.757)) and latency for the left eye (r = 0.042, OR = 0.966 (0.934-0.999)) at the onset of disease were predictive factors for achieving NEDA-3. A normal VEP at the beginning of RRMS increases the chance of reaching NEDA-3 by about six times.

Different visual evoked potentials in neuromyelitis optica spectrum disorder-related optic neuritis and idiopathic demyelinating optic neuritis: a prospective longitudinal analysis

BackgroundTo investigate different visual evoked potential (VEP) patterns in neuromyelitis optica spectrum disorder-related optic neuritis (NMOSD-ON) and idiopathic demyelinating optic neuritis (IDON).MethodsThis was a longitudinal, prospective, case-control study. Eighty-four Chinese patients with acute optic neuritis were enrolled, including 26 NMOSD-ON patients and 58 IDON patients. All the patients underwent best-corrected visual acuity (BCVA) and full-field pattern reversal VEP recordings at the onset, 1 month, 3 months, and 6 months.ResultsWithin 15′ checks, the NMOSD-ON patients had more severe VEP amplitude reduction at 6 months (2.39 ± 4.63 μV vs. 6.96 ± 8.88 μV, P = 0.034). However, the IDON patients showed more frequently normal VEP response at 3 months (24.0% vs. 4.5%, P = 0.017), and only prolonged P100 peak latency with normal amplitude (L) at 6 months (30.0% vs. 57.8%, P = 0.048). Within 60′ checks, no significant difference in VEP parameters between the two groups was found at each follow-up (P > 0.05). ConclusionsThe NMOSD-ON patients showed more severe axonal damage and worse axonal recovery than the IDON patients. VEP elicited by smaller check size was more sensitive to visual pathway abnormality in NMOSD-ON.

Individual differences in visual evoked potential latency are associated with variance in brain tissue volume in people with multiple sclerosis: An analysis of brain function-structure correlates

Visual evoked potentials (VEP) index visual pathway functioning, and are often used for clinical assessment and as outcome measures in people with multiple sclerosis (PwMS). VEPs may also reflect broader neural disturbances that extend beyond the visual system, but this possibility requires further investigation. In the present study, we examined the hypothesis that delayed latency of the P100 component of the VEP would be associated with broader structural changes in the brain in PwMS. We obtained VEP latency for a standard pattern-reversal checkerboard stimulus paradigm, in addition to Magnetic Resonance Imaging (MRI) measures of whole brain volume (WBV), gray matter volume (GMV), white matter volume (WMV), and T2-weighted fluid attenuated inversion recovery (FLAIR) white matter lesion volume (FLV). Correlation analyses indicated that prolonged VEP latency was significantly associated with lower WBV, GMV, and WMV, and greater FLV. VEP latency remained significantly associated with WBV, GMV, and WMV even after controlling for the variance associated with inter-ocular latency, age, time between VEP and MRI assessments, and other MRI variables. VEP latency delays were most pronounced in PwMS that exhibited low volume in both white and gray matter simultaneously. Furthermore, PwMS that had delayed VEP latency based on a clinically relevant cutoff (VEP latency ≥ 113 ms) in both eyes had lower WBV, GMV, and WMV and greater FLV in comparison to PwMS that had normal VEP latency in one or both eyes. The findings suggest that PwMS that have delayed latency in both eyes may be particularly at risk for exhibiting greater brain atrophy and lesion volume. These analyses also indicate that VEP latency may index combined gray matter and white matter disturbances, and therefore broader network connectivity and efficiency. VEP latency may therefore provide a surrogate marker of broader structural disturbances in the brain in MS.

Cerebral Visual Impairment Characterized by Abnormal Visual Orienting Behavior With Preserved Visual Cortical Activation.

PurposeChildren with cerebral visual impairment (CVI) often have abnormal visual orienting behaviors due to impaired or damaged visual cortex. Alternatively, visual-cortical function is intact but visual information is not transformed downstream into an appropriate oculomotor output (visuomotor dysfunction). We examined visual, anatomic, and oculomotor assessments to distinguish visuomotor dysfunction from CVI associated with severely reduced visual-cortical response.MethodsWe reviewed the medical records from children with CVI having abnormal visual orienting behaviors, normal ocular examinations, and born near term. Relevant data were visual evoked potentials (VEPs), Teller card acuity, eye movements recorded by video-oculography (VOG), and neuroimaging (magnetic resonance imaging [MRI]) including diffusion tensor imaging (DTI) tractography.ResultsThirty subjects had visuomotor dysfunction based on a normal VEP; of these 33% had a normal MRI and 67% had white matter abnormalities associated with metabolic disease and/or decreased volume of brain parenchyma. VOG recordings showed smooth pursuit gains were uniformly reduced and saccades were dysmetric but followed the main sequence. Ten subjects had severe CVI based on VEPs at noise levels; visual acuities and MRI findings overlapped those of the visuomotor dysfunction group. Developmental delay, seizures, microcephaly, and hypotonia were common across all groups. All subjects with an abnormal conventional MRI had abnormal metrics on DTI tractography from the occipital lobe.ConclusionsA subset of patients with CVI have abnormal visual orienting behaviors despite a normal VEP (visuomotor dysfunction). A majority have abnormal white matter metrics on tractography suggesting a downstream defect in sensorimotor transformation. Clinically, visuomotor dysfunction is indistinguishable from severe CVI.

Visual outcomes in children with syndromic craniosynostosis: a review of 165 cases.

To determine visual outcomes and prevalence of amblyogenic risk factors in children with Apert, Crouzon, Pfeiffer and Saethre-Chotzen syndromes. We conducted a single-centre, retrospective chart review of patients assessed at our unit between October 2000 and May 2017. Our outcome measures were as follows: ageat first and last examination, refraction, horizontal ocular alignment, alphabet pattern deviations, anterior segment appearance, fundus examination findings, visual evoked potentials (VEPs) and genetics. The study's primary endpoint was the proportion of children achieving best-corrected visual acuity (BCVA) ≥ 6/12 in the better eye at final visit, as per UK driving standards. 165 patients were included in this study. Breakdown of diagnoses was as follows: Crouzon (n = 60), Apert (n = 57), Pfeiffer (n = 14) and Saethre-Chotzen (n = 34). 98 patients were male. Of 133 patients with full BCVA data available, 76.7% achieved BCVA ≥ 6/12 in the better eye. Of 122 patients, anisometropia >1.00 dioptre sphere (DS) affected 18.9% and astigmatism ≥1.00DS in at least one eye affected 67.2%. Of 246 eyes, 48.4% had oblique astigmatism. Of 165 patients, 60 had exotropia and 12 had esotropia. 48 of 99 patients demonstrated 'V' pattern. On multivariable logistic regression, nystagmus (p = 0.009) and ON involvement (p = 0.001) were associated with decreased vision in the worse eye. Normal VEPs were associated with better BCVA (p = 0.036). There was a high prevalence of amblyogenic factors, however, the majority achieved BCVA ≥ 6/12 in their better eye. Optic neuropathy and nystagmus had the most significant impact on vision. VEPs can help the in overall assessment of visual function.

MS optic neuritis-induced long-term structural changes within the visual pathway.

BackgroundThe visual pathway is commonly involved in multiple sclerosis (MS), even in its early stages, including clinical episodes of optic neuritis (ON). The long-term structural damage within the visual compartment in patients with ON, however, is yet to be elucidated.ObjectiveOur aim was to characterize visual system structure abnormalities using MRI along with optical coherence tomography (OCT) and pattern-reversal visual evoked potentials (VEPs) depending on a single history of ON.MethodsTwenty-eight patients with clinically definitive MS, either with a history of a single ON (HON) or without such history and normal VEP findings (NON), were included. OCT measures comprised OCT-derived peripapillary retinal nerve fiber layer (RNFL) and macular ganglion cell/inner plexiform layer (GCIPL) thickness. Cortical and global gray and white matter, thalamic, and T2 lesion volumes were assessed using structural MRI. Diffusion-weighted MRI-derived measures included fractional anisotropy (FA), mean (MD), radial (RD), and axial (AD) diffusivity within the optic radiation (OR).ResultsMean (SD) duration after ON was 8.3 (3.7) years. Compared with the NON group, HON patients showed significant RNFL (p = 0.01) and GCIPL thinning (p = 0.002). OR FA (p = 0.014), MD (p = 0.005), RD (p = 0.007), and AD (p = 0.004) were altered compared with NON. Global gray and white as well as other regional gray matter structures did not differ between the 2 groups.ConclusionA single history of ON induces long-term structural damage within the retina and OR suggestive of both retrograde and anterograde neuroaxonal degeneration.

CHARACTERISTICS OF VISUAL EVOKED POTENTIAL IN OPTIC NEURITIS PATIENTS AT SANGLAH GENERAL HOSPITAL

Background: Optic neuritis is an inflammation of the optic nerve. Inflammation may occur due to primary demyelination processes e.g. multiple sclerosis, or secondary due to other causes. Visual Evoked Potential (VEP) is an objective examination that can detect the optic nerve lesion. A characteristic finding of VEP in optic neuritis patient is prolongation of VEP latency that can last for several years. This study was conducted to determine the characteristics of VEP in optic neuritis patients at Sanglah General Hospital, Denpasar, Bali, Indonesia. Methods: A descriptive cross-sectional study was performed, involving subjects with optic neuritis admitted to Neurology clinic at Sanglah General Hospital 2017-2019. All VEP recordings were interpreted by a certified neurophysiology consultant. The collected data subsequently processed and analyzed statistically. Results: A total of 42 subjects with optic neuritis were admitted, by which 17 of them were males and 25 females, respectively, with average age of 38.4 years old. The median latency of P100 wave (in milliseconds) at O1 was 123.0 (left) and 118.0 (right); at Oz was 115.0 (left) and 117.5 (right); at O2 was 118.5 (left) and 120.0 (right). Median amplitudes were 3.15 and 3.0 for left and right eye respectively. The conclusions of VEP recordings were: 23.8% subjects suffered from left optic nerve lesion, 14.1% right optic nerve lesion, 45.2% both left and right optic nerve lesion and 16.7% with normal VEP recording. Conclusion: Optic neuritis patients at Neurology clinic in Sanglah General Hospital was predominantly female with average age 38.4 years old. The characteristics of VEP in this group was prolonged of P100 latency with low amplitudes. The conclusion of VEP recordings was predominantly left and right optic nerve lesion.

Visual evoked potential in multiple sclerosis and neuromyelitis optica spectrum disorder: A comparative study

Objectives The neuromyelitis optica spectrum disorder (NMOSD) was differentiated from relapsing-remitting multiple sclerosis (MS) by clinical, laboratory and physiopathological findings, including the presence of anti-aquaporin 4 (AQP4-Ab) antibody. Visual evoked potentials (VEP) are often used for the diagnosis of MS. However, the features of these VEP in the NMOSD have not been studied in detail. Our aim is to determine the epidemiological, clinical and especially neurophysiological (VEP) differences between MS and NMOSD. Methods Fourteen patients with NMOSD and 14 patients with RRMS were included in this study. The patients’ neurological symptoms and signs were examined and their VEP recorded. Results The mean age at onset of the patients with NMOSD was 43.21 years, which was older than that of the patients with RRMS (P = 0.017). The ratio of female patients with NMOSD was higher than that with RRMS (P = 0.012). The periods from onset to diagnosis were similar between the two groups. The prevalence of bilateral visual disturbance was higher in the NMOSD group (78.57%). Patients with RRMS presented a P100 latency and/or amplitude impairment in 6 asymptomatic eyes (21.42%). While in patients with NMOSD, there were 4 asymptomatic eyes that had all normal VEP. In VEP, 17.9% of NMOSD eyes presented no response and only 3.6% of MS eyes and the P100 amplitude impairment was predominant in NMOSD. Conclusion Sometimes, it remains critical to differentiate a MS from an NMOSD especially when the specific antibody is negative. VEP results can point to one of the two diseases even at an early stage.

Visual Evoked Potential in Children With Developmental Disorders: Correlation With Neurodevelopmental Outcomes.

ObjectiveTo investigate the neurodevelopmental outcomes in children with developmental disorder according to visual evoked potential (VEP) results.MethodsWe retrospectively analyzed children who visited our Department of Pediatric Rehabilitation Medicine with a chief complaint of developmental disability from January 2001 to July 2015. Of the 549 medical records reviewed, 322 children younger than 42 months who underwent both Bayley Scales of Infant and Toddler Development second edition (BSID-II) and VEP studies were enrolled. We compared the development of 182 children with normal VEP latency and 140 children with delayed VEP latency results using the BSID-II results. The Mann-Whitney U-test was used to analyze the differences between the two groups.ResultsThere were no significant differences in baseline characteristics between the two groups. The delayed VEP latency group showed a significant delay in BSID-II index scores and developmental quotients compared with the normal VEP latency group. In addition, a comparative analysis of developmental quotients of mental and psychomotor domains according to age (younger than 12 months, 12–23 months, and 24–42 months) revealed significantly lower values in children with delayed VEP latency compared to children with normal VEP latency, younger than 12 months and from 12 to 23 months.ConclusionChildren with delayed VEP latency showed more developmental delay than children with normal VEP latency. It is suggested that VEP can be easily applied to children with suspected developmental delay when physicians have concerns about visual impairment. Furthermore, it is proposed that VEP results could provide an insight into children's development and serve as early indicators for consultation with an ophthalmologist for the existing problem.

Normative values of visual evoked potentials’ latencies and amplitudes in adults

Background: Visual Evoked Potentials (VEP) are used to assess the visual pathway through the optic nerves and brain. A normal VEP response to a stimulus is a positive occipital peak that occurs at a mean latency of 100 ms. The value of VEP parameters can be affected by unique physiological and non-physiological factors; some of which can be controlled, while others cannot. Thus, each VEP laboratory needs its own set of normative values.

Microstructure changes of occipital white matter are responsible for visual problems in the 3-4-year-old very low birth weight children.

Purpose:The main aim of the study was to evaluate which factors affect the long-time visual function in preterm children, whether it is prematurity or retinopathy of prematurity or perhaps disturbances in the visual pathway.Materials and Methods:Fifty-eight children with mean birth weight 1016 g (range 520–1500 g) were evaluated at mean age 48 months (range 42–54 months). All children underwent magnetic resonance imaging (MRI) studies, visual evoked potentials (VEPs), and the Developmental Test of Visual Perception (DTVP). The MRI evaluation included diffusion tensor imaging and fractional anisotropy (FA), and colored orientation maps were calculated for each subject. Based on the results of the VEP evaluation, children were divided into two groups: A-abnormal results of VEP (n = 16) and B-normal VEP results (comparison group, n = 42).Results:FA values of inferior left and right occipital white matter (OWM) were lower in the group of children with abnormal VEP compared to the comparison group (0.34 ± 0.06 vs. 0.38 ± 0.06; P = 0.047; 0.31 ± 0.04 vs. 0.36 ± 0.06; P = 0.007, respectively). Furthermore, there were correlations between the latency (r = −0.35; P = 0.01) and amplitude (r = 0.31; P = 0.02) and FA in OWM. Children with abnormal VEP had lower DTVP scores as compared with children with normal VEP results (88 ± 18 vs. 95 ± 16 points, P = 0.048). Finally, a multivariate logistic regression revealed that FA of the inferior OWM was the only independent risk factor for the abnormal VEP (P = 0.04).Conclusion:Visual perception, VEPs, and white matter microstructural abnormalities in very low birth weight children at the age of 3–4 are significantly correlated.

Fractal Dimension Analysis of Transient Visual Evoked Potentials: Optimisation and Applications.

PurposeThe visual evoked potential (VEP) provides a time series signal response to an external visual stimulus at the location of the visual cortex. The major VEP signal components, peak latency and amplitude, may be affected by disease processes. Additionally, the VEP contains fine detailed and non-periodic structure, of presently unclear relevance to normal function, which may be quantified using the fractal dimension. The purpose of this study is to provide a systematic investigation of the key parameters in the measurement of the fractal dimension of VEPs, to develop an optimal analysis protocol for application.MethodsVEP time series were mathematically transformed using delay time, τ, and embedding dimension, m, parameters. The fractal dimension of the transformed data was obtained from a scaling analysis based on straight line fits to the numbers of pairs of points with separation less than r versus log(r) in the transformed space. Optimal τ, m, and scaling analysis were obtained by comparing the consistency of results using different sampling frequencies. The optimised method was then piloted on samples of normal and abnormal VEPs.ResultsConsistent fractal dimension estimates were obtained using τ = 4 ms, designating the fractal dimension = D2 of the time series based on embedding dimension m = 7 (for 3606 Hz and 5000 Hz), m = 6 (for 1803 Hz) and m = 5 (for 1000Hz), and estimating D2 for each embedding dimension as the steepest slope of the linear scaling region in the plot of log(C(r)) vs log(r) provided the scaling region occurred within the middle third of the plot. Piloting revealed that fractal dimensions were higher from the sampled abnormal than normal achromatic VEPs in adults (p = 0.02). Variances of fractal dimension were higher from the abnormal than normal chromatic VEPs in children (p = 0.01).ConclusionsA useful analysis protocol to assess the fractal dimension of transformed VEPs has been developed.

Alterations of the optic pathway between unilateral and bilateral optic nerve damage in multiple sclerosis as revealed by the combined use of advanced diffusion kurtosis imaging and visual evoked potentials

ObjectivesWe investigated changes in the optic tract and optic radiation in patients with multiple sclerosis (MS) by comparing unilateral and bilateral optic nerve damage assessed based on visual evoked potentials (VEPs) using advanced diffusion MR metrics. MethodsIn 21 MS patients, diffusion MRI was performed. Maps of fractional anisotropy, apparent diffusion coefficient (ADC), and mean kurtosis (MK) were computed. On the basis of the P100 latency in VEPs, the MS patients were divided into three groups: bilateral (n=7), unilateral (n=7), and no abnormality (n=7). Their optic tracts and optic radiations were analyzed with diffusion MRI-based fiber tracking. We also investigated the correlations between diffusion parameters and VEPs (n=21). ResultsIn the optic tract, the diffusion changes in each of the three groups showed step-like changes. The diffusion changes in the optic radiations of the unilateral group were similar to those in the normal VEP group. Only the bilateral group showed significantly higher ADC and lower MK relative to the other two groups (P<0.05, Steel–Dwass multiple-comparison test). A significant positive correlation between VEP latency and ADC and a significant negative correlation between VEP latency and MK were observed (P<0.01, Spearman's correction). ConclusionsWe first evaluated the relationship between VEPs and DKI and concluded that the lateral geniculate nucleus may compensate for unilateral damage in the pre-geniculate optic pathway via neural plasticity.

Visual evoked potentials in patients after methanol poisoning.

We report the results of the visual evoked potentials (VEP) examination in patients after severe poisoning by methanol. The group of 47 patients (38 males and 9 females) was assembled out of persons who survived an outbreak of poisoning by the methanol adulterated alcohol beverages, which happened in the Czech Republic in 2012-2013. The visual evoked potentials examination was performed using monocular checkerboard pattern-reversal stimulation. Two criteria of abnormality were chosen: missing evoked response, and wave P1 latency > 117 ms. Non-parametric statistical methods (median, range, and the median test) were used to analyze factors influencing the VEP abnormality. The visual evoked potential was abnormal in 20 patients (43%), 5 of them had normal visual acuity on the Snellen chart. The VEP abnormality did not correlate significantly with initial serum concentrations of methanol, formic acid or lactate; however, it showed statistically significant inverse relation to the initial serum pH: the subgroup with the abnormal VEP had significantly lower median pH in comparison with the subgroup with the normal VEP (7.16 vs. 7.34, p = 0.04). The abnormality was not related to chronic alcohol abuse. The visual evoked potentials examination appeared sensitive enough to detected even subclinical impairment of the optic system. Metabolic acidosis is likely to be the key factor related to the development of visual damage induced by methanol. The examination performed with a delay of 1-9 months after the poisoning documented the situation relatively early after the event. It is considered as a baseline for the planned long-term follow-up of the patients, which will make it possible to assess the dynamics of the observed changes, their reversibility, and the occurrence of potential late sequelae.

Visual evoked potentials in children and adolescence with neurofibromatosis type 1

Children with neurofibromatosis type 1 (NF1) have an increased risk of developing optic pathway gliomas (OPGs) during childhood. The role of visual evoked potential (VEP) in the management of children with NF1, are controversial. The purpose of this investigation was to determine: if VEP abnormalities could be identified in children with NF1 with no MRI evidence of OPGs; and can screening for OPG in patient with NF1 be performed with VEP testing? We retrospectively reviewed VEP records of the 29 patients with NF1. Pattern reversal visual evoked potentials (PR-VEP) were performed using standardized technique, on Medelec Sapphire Premiere device. A total of 29 children and adolescents were examined. Of those, 18 had pathological VEP: eight with the P100 latency prolongation, six with decreased amplitude, four with significant interocular amplitude difference. One of four patients with OPG has normal VEP. Our study showed that some degree of abnormalities could be identified in a significant number of patients, independently of presence of OPG. This may represent a marker of abnormal visual processing. Despite their limitations, VEPs would have provide useful adjunct to clinical ophthalmologic review to identified children at risk for visual impairment.

Visual Evoked Potentials: Normative Values and Gender Differences.

Visual evoked potentials (VEP) are used to assess the visual pathways through the optic nerves and brain. A normal VEP response to a pattern-reversal stimulus is a positive mid occipital peak that occurs at a mean latency of 100 ms. VEP may be affected by variety of physiological factors including age, sex, visual acuity and pupillary size. The present study was performed on healthy medical students to determine the normative values and to investigate the effect of sex and anthropometric parameters on visual evoked potentials. The study was conducted on 100 healthy medical students of Government Medical College, Patiala in the age group of 17-20 years, in which there were 50 males and 50 females. The anthropometric parameters including age, height, weight, BMI, BSA and Head circumference were recorded in all the subjects. VEP was recorded with a PC based, 2 channel, RMS EMG EP mark II machine and standard silver-silver chloride disc electrodes. A VEP monitor displaying checker board was used to give the pattern reversal stimulus. The VEP parameters recorded were latencies to N70, P100 and N155 waves, and peak to peak amplitude of P100 wave. Our results showed that the latencies of N70, P100 and N155 waves were significantly longer in males as compared to females. The amplitude of P100 wave was higher in females in both left and right eye as compared to males. No significant correlation was found between VEP parameters and head circumference in both male and female subjects in our study. Gender is an important variable affecting the VEP. The exact reason of gender difference is not clear, but it may be related to anatomical or endocrinal differences in the two sexes.

Contributing factors to VEP grating acuity deficit and inter-ocular acuity difference in children with cerebral visual impairment

To investigate contributing factors to visual evoked potential (VEP) grating acuity deficit (GAD) and inter-ocular acuity difference (IAD) measured by sweep-VEPs in children with cerebral visual impairment (CVI). VEP GAD was calculated for the better acuity eye by subtracting acuity thresholds from mean normal VEP grating acuity according to norms from our own laboratory. Deficits were categorized as mild (0.17 ≤ deficit < 0.40 log units), moderate (0.40 ≤ deficit < 0.70 log units) or severe (deficit ≥0.70 log units). Maximum acceptable IAD was 0.10 log units. A group of 115 children (66 males-57 %) with ages ranging from 1.2 to 166.5 months (median = 17.7) was examined. VEP GAD ranged from 0.17 to 1.28 log units (mean = 0.68 ± 0.27; median = 0.71), and it was mild in 23 (20 %) children, moderate in 32 (28 %) and severe in 60 (52 %). Severe deficit was significantly associated with older age and anti-seizure drug therapy. IAD ranged from 0 to 0.49 log units (mean = 0.06 ± 0.08; median = 0.04) and was acceptable in 96 (83 %) children. Children with strabismus and nystagmus had IAD significantly larger compared to children with orthoposition. In a large cohort of children with CVI, variable severity of VEP GAD was found, with more than half of the children with severe deficits. Older children and those under anti-seizure therapy were at higher risk for larger deficits. Strabismus and nystagmus provided larger IADs. These results should be taken into account on the clinical management of children with this leading cause of bilateral visual impairment.

Retinal Function and Neural Conduction Along the Visual Pathways in Affected and Unaffected Carriers With Leber's Hereditary Optic Neuropathy

We assessed retinal ganglion cell (RGC) function, and established a correlation between the neural conduction along the visual pathways and the retinal involvement in Leber's hereditary optic neuropathy (LHON). A total of 39 individuals carrying a LHON mutation (mean age, 33.35 ± 8.4 years), LHON-unaffected (LU, 22 eyes) or LHON-affected (LA, 17 eyes), underwent visual acuity and visual field examinations. A total of 22 age-similar normal subjects (mean age, 38.2 ± 6.0 years) served as controls. In all subjects, simultaneous pattern electroretinograms (PERGs) and visual evoked potentials (VEPs) were recorded in response to 60-minute (60') and 15-minute (15') checkerboard stimuli. When compared to controls, LU eyes did not show any statistically significant difference in 60' and 15' VEP P100 implicit times (ITs), VEP N75-P100 amplitudes, and 60' PERG P50 ITs, whereas 15' PERG P50-N95 amplitudes were significantly (P < 0.01) reduced. When compared to control and LU eyes, LA eyes showed significant differences in PERG and VEP ITs, and amplitudes with both stimulations (60' and 15' checks). No significant correlations between PERG and VEP parameters were found in LU eyes, while in LA eyes, PERG P50 and VEP P100 ITs correlated significantly only when using 60' checks. The LHON-unaffected eyes showed a retinal dysfunction detected by abnormal PERG responses that was not associated with changes along the visual pathways assessed by normal VEP responses. In LA eyes, the impaired neural conduction recorded by VEPs in response to larger (60' VEP responses) and smaller (15' VEP responses) checks were associated and not associated, respectively, with the detected retinal dysfunction.