Quantitative assessment of visual pathway function in blind retinitis pigmentosa patients.

OBJECTIVE: The current methods used to assess visual function in blind retinitis pigmentosa (RP) patients are mostly subjective. We aimed to identify effective, objective methods. METHODS: We enrolled patients diagnosed with blindness associated with RP; we finally selected 26 patients (51 eyes) with a visual field radius less than 10 degrees and divided them into the following 4 groups by best-corrected visual acuity (BCVA): group 1, no light perception (NLP, 4 eyes); group 2, light perception (LP, 12 eyes); group 3, hand movement or finger counting (faint form perception, FFP, 22 eyes); and group 4, BCVA from 0.1 to 0.8 (form perception, FP, 13 eyes). All patients underwent optometry, optical coherence tomography (OCT), color fundus photography, fundus autofluorescence (FAF), full field electroretinography (ffERG), pattern electroretinography (PERG), multifocal electroretinography (mf-ERG), pattern visual evoked potential (PVEP), flash visual evoked potential (FVEP), and pupillary light response (PLR) assessments. Five patients in groups 1, 2, and 3 (1, 2, and 2 subjects, respectively) underwent functional magnetic resonance imaging (fMRI) scans and were compared with five healthy subjects. RESULTS: The outer plexiform layer was thinner in group 1, and the outer nuclear layer was thinner in groups 1 and 2. The ffERG, PERG, and mf-ERG findings were unrecordable in all four groups. The P2 amplitude of the FVEP was significantly lower in groups 1 and 2, while the P100 amplitude of the PVEP was higher in groups 2, 3 and 4 than in group 1. After white- and blue-light stimuli, the PLR thresholds in the patients without form perception were significantly higher. The threshold of the PLR stimulated by blue and white light was negatively correlated with the amplitudes of P2 and P100. Moreover, the fMRI findings showed that some RP patients have significant visual cortex activation in response to certain types of stimulation. However, statistical analysis was not performed because of the small number of cases. CONCLUSIONS: OCT, VEP, PLR and fMRI assessments can evaluate residual visual pathway function in blind RP patients. SIGNIFICANCE: Our study may have clinical significance for the potential prediction of RP patient prognoses and the effects after clinical trials.

Assessment of the visual pathways in patients with neurofibromatosis-1 by 3S-space technique with 3-Tesla MRI

Background/aim/AIM: We aimed to evaluate the size/tortuosity of the optic nerve (ON) and the dilatation of the ON sheath (ONS) in neurofibromatosis type 1 (NF-1) patients with 3T-MRI, and to assess the usefulness of 3D-SPACE in imaging the optic pathway, ON, and ONS in NF-1 patients. Materials and methods: Twenty consecutive NF-1 patients without optic pathway glioma (OPG) (Group 1), 16 consecutive NF-1 patients with OPG (Group 2), and 19 controls were included in this study. The thickness and tortuosity of the ON and the diameter of the ONS were measured on STIR and 3D-SPACE images. Results: The thickness of the ON was similar in all groups on STIR images (P>0.05). The mean ONS diameter was higher in Group 2 with this sequence (P=0.009). Controls had significantly lower grades of ON tortuosity than Groups 1 and 2 (P=0.001), and Group 1 had significantly lower ON tortuosity compared to Group 2 (P=0.001). Severe tortuosity was only detected in Group 2. Conclusion: ON tortuosity and ONS diameter were increased in NF-1 patients in the presence of OPG. High-resolution cranium imaging with the 3D-SPACE technique using 3T-MRI seems to be helpful for detection of the optic pathway morphology and pathologies in NF-1 patients.

Assessment of vision in concussion.

PURPOSE OF REVIEW: To review emerging vision-based assessments in the evaluation of concussion. RECENT FINDINGS: Involvement of the visual pathways is common following concussion, the mildest form of traumatic brain injury. The visual system contains widely distributed networks that are prone to neurophysiologic changes after a concussion, resulting in visual symptoms and ocular motor dysfunction. Vision-based testing is increasingly used to improve detection and assess head injury. Several rapid automatized naming (RAN) tasks, such as the King-Devick test and the Mobile Universal Lexicon Evaluation System, show capacity to identify athletes with concussion. Video-oculography (VOG) has gained widespread use in eye-tracking and gaze-tracking studies of head trauma from which objective data have shown increased saccadic latencies, saccadic dysmetria, errors in predictive target tracking, and changes in vergence in concussed individuals. SUMMARY: RAN tasks demonstrate promise as rapid screening tools for concussion. Further investigation will involve assessment of the role for age, characterization of learning effects over repeated measurements, and identification of optimal thresholds for clinically significant performance decrements. Various RAN tasks are likely to be functionally distinct, engaging different neural networks according to the demands of each task. Measures of saccades, smooth pursuit eye-movements, the vestibulo-ocular reflex and, more recently, disparity vergence are candidate vision-based markers for concussion. Work to adopt these assessments to the sideline or clinical environments is ongoing.

Functional and morphological assessment of ocular structures and follow-up of patients with early-stage Parkinson's disease.

PURPOSE: To evaluate and follow-up of functional and morphological changes of the optic nerve and ocular structures prospectively in patients with early-stage Parkinson's disease. MATERIALS AND METHODS: Nineteen patients with a diagnosis of early-stage Parkinson's disease and 19 age-matched healthy controls were included in the study. All participants were examined minimum three times at the intervals of at least 6 month following initial examination. Pattern visually evoked potentials (VEP), contrast sensitivity assessments at photopic conditions, color vision tests with Ishihara cards and full-field visual field tests were performed in addition to measurement of retinal nerve fiber layer (RNFL) thickness of four quadrants (top, bottom, nasal, temporal), central and mean macular thickness and macular volumes. RESULTS: Best corrected visual acuity was observed significantly lower in study group within all three examinations. Contrast sensitivity values of the patient group were significantly lower in all spatial frequencies. P100 wave latency of VEP was significantly longer, and amplitude was lower in patient group; however, significant deterioration was not observed during the follow-up. Although average peripapillary RNFL thickness was not significant between groups, RNFL thickness in the upper quadrant was thinner in the patient group. While there was no difference in terms of mean macular thickness and total macular volume values between the groups initially, a significant decrease occurred in the patient group during the follow-up. During the initial and follow-up process, a significant deterioration in visual field was observed in the patient group. CONCLUSION: Structural and functional disorders shown as electro-physiologically and morphologically exist in different parts of visual pathways in early-stage Parkinson's disease.

Psychophysical assessment of koniocellular pathway in patients with schizophrenia versus healthy controls.

This study was designed to perform psychophysical assessment of koniocellular pathway in patients with schizophrenia versus healthy controls. A total of 26 patients diagnosed with schizophrenia and 15 healthy controls were included. Snellen Visual Acuity Chart scores and Short Wavelength Automated Perimetry (SWAP) visual field testing including global visual field indices [mean deviation (MD), pattern standard deviation (PSD), test time (min)], reliability parameters [false negative responses (%), false positive responses (%) and fixed losses (%)] and average threshold sensitivity [central (parafovea), peripheral area, and four quadrants] were recorded in both groups. Significantly lower MD scores, higher PSD scores and lower average threshold sensitivity at each location across the visual field were noted in schizophrenia relative to control group. In conclusion, our findings revealed a deficit in koniocellular pathway with impaired SWAP global indices and lower threshold sensitivity at each location across the visual field among chronic schizophrenic patients as compared with control subjects. Our findings emphasize potential application of SWAP outside its original intended purpose as a glaucoma test, to provide deeper understanding of the specific contribution of lateral geniculate nucleus to the visual and cognitive disturbances of schizophrenia.

Multichannel visual evoked potentials in the assessment of visual pathways in children with marked brain abnormalities.

PURPOSE: To demonstrate how multichannel visual evoked potentials (VEPs) can provide quantitative measures of visual function in children with marked cortical anatomy abnormalities. METHODS: Four children with marked brain pathology (2 holoprosencephaly, 2 giant interhemispheric cysts with hydrocephalus) underwent pattern reversal and flash VEP recordings from 16 equally distributed electrodes. Voltage maps of the major VEP components were constructed, and their distributions were compared to the magnetic resonance imaging (MRI) findings. RESULTS: No reproducible responses were evident in 1 case, and responses were present, but, as expected based on the MRI finding, not over the occipital electrodes in 3 cases. Thus, the standard clinical VEP electrode placement would not have detected responses. The distribution of responses during monocular testing obtained in 2 cases suggested normal decussation of the visual pathways at the chiasm, and voltage mapping indicated which part of the abnormally positioned brain tissue is functional visual cortex. CONCLUSIONS: In children with markedly abnormal brain anatomy, multichannel VEP recordings can provide quantifiable measures of visual pathway function detected in atypical locations. VEPs provide a quantifiable measure of visual function that could be used to assist in determining visual acuity levels, and offered a baseline for monitoring in the context of raised intracranial pressure. These recordings were also able to identify functional anatomical structures that were not apparent on MRI. In a clinical setting, the use of additional recordings from nonstandard electrode placement based on the MRI findings is suggested.

Rapid and Objective Assessment of Neural Function in Autism Spectrum Disorder Using Transient Visual Evoked Potentials.

OBJECTIVE: There is a critical need to identify biomarkers and objective outcome measures that can be used to understand underlying neural mechanisms in autism spectrum disorder (ASD). Visual evoked potentials (VEPs) offer a noninvasive technique to evaluate the functional integrity of neural mechanisms, specifically visual pathways, while probing for disease pathophysiology. METHODS: Transient VEPs (tVEPs) were obtained from 96 unmedicated children, including 37 children with ASD, 36 typically developing (TD) children, and 23 unaffected siblings (SIBS). A conventional contrast-reversing checkerboard condition was compared to a novel short-duration condition, which was developed to enable objective data collection from severely affected populations who are often excluded from electroencephalographic (EEG) studies. RESULTS: Children with ASD showed significantly smaller amplitudes compared to TD children at two of the earliest critical VEP components, P60-N75 and N75-P100. SIBS showed intermediate responses relative to ASD and TD groups. There were no group differences in response latency. Frequency band analyses indicated significantly weaker responses for the ASD group in bands encompassing gamma-wave activity. Ninety-two percent of children with ASD were able to complete the short-duration condition compared to 68% for the standard condition. CONCLUSIONS: The current study establishes the utility of a short-duration tVEP test for use in children at varying levels of functioning and describes neural abnormalities in children with idiopathic ASD. Implications for excitatory/inhibitory balance as well as the potential application of VEP for use in clinical trials are discussed.

Multifocal VEP assessment of optic neuritis evolution.

OBJECTIVE: To evaluate multifocal visual evoked potentials (mfVEP) changes in optic neuritis (ON) and fellow eyes during first year after the attack. METHODS: Eighty-seven patients and twenty-five controls were examined. Patients were classified as multiple sclerosis (MS) group, high risk (HR) or low risk (LR) groups for conversion to MS. mfVEP recordings and retinal nerve fiber layer (RNFL) thickness were analyzed. RESULTS: Recovery of amplitude and shortening of latency was fastest within the first 3months. The largest amplitude reduction and longest latency delay of the ON eye were recorded in the MS group. This was accompanied by deterioration of both parameters in fellow eyes (p<0.03). mfVEP remained stable in fellow eyes of the LR group. Inter-eye asymmetry showed similar amount of amplitude reduction and latency delay in all three groups. RNFL thickness strongly correlated with mfVEP amplitude as early as 3 months after ON (R(2)=0.6, p=0.001). CONCLUSION: mfVEP amplitude is an early predictor of post-ON axonal loss. The apparent more severe involvement of ON eyes in the MS subgroup may be due to subclinical inflammation along the visual pathway. SIGNIFICANCE: Severity of amplitude reduction and latency delay after episode of ON is not MS-related. Retro-chiasmal demyelination is a possible factor contributing to amplitude and latency differences between MS and non-MS patients.

Functional assessment of the visual pathway with multifocal visual evoked potentials, and their relationship with disability in patients with multiple sclerosis.

OBJECTIVE: To objectively evaluate the visual function, and the relationship between disability and optic nerve dysfunction, in patients with multiple sclerosis (MS) and optic neuritis (ON), using multifocal visual evoked potentials (mfVEP). METHODS: This observational, cross-sectional study assessed 28 consecutive patients with clinically definite MS, according to the McDonald criteria, and 19 age-matched healthy subjects. Disability was recorded using the Expanded Disability Status Scale (EDSS) score. The patients' mfVEP were compared to their clinical, psychophysical (Humphrey perimetry) and structural (optic coherence tomography (OCT)) diagnostic test data. RESULTS: We observed a significant agreement between mfVEP amplitude and Humphrey perimetry/OCT in MS-ON eyes, and between mfVEP amplitude and OCT in MS but non-ON eyes. We found significant differences in EDSS score between patients with abnormal and normal mfVEP amplitudes. Abnormal mfVEP amplitude defects (from interocular and monocular probability analysis) were found in 67.9% and 73.7% of the MS-ON and MS-non-ON group eyes, respectively. Delayed mfVEP latencies (interocular and monocular probability analysis) were seen in 70.3% and 73.7% of the MS-ON and MS-non-ON groups, respectively. CONCLUSIONS: We found a significant relationship between mfVEP amplitude and disease severity, as measured by EDSS score, that suggested there is a role for mfVEP amplitude as a functional biomarker of axonal loss in MS.

Evaluation of magnocellular pathway abnormalities in schizophrenia: a frequency doubling technology study and clinical implications / Avaliação das alterações da via magnocelular na esquizofrenia usando FDT e suas implicações clínicas

BACKGROUND: Visual processing deficits have been reported for patients with schizophrenia. Previous studies demonstrated differences in early-stage processing of schizophrenics, although the nature, extent, and localization of the disturbance are unknown. The magnocellular and parvocellular visual pathways are associated with transient and sustained channels, but their respective contributions to schizophrenia-related visual deficits remains controversial. PURPOSE: The aim of this study was to evaluate magnocellular dysfunction in schizophrenia using frequency doubling technology. METHODS: Thirty-one patients with schizophrenia and 34 healthy volunteers were examined. Frequency doubling technology testing was performed in one session, consisting of a 15-minute screening strategy followed by the C-20 program for frequency doubling technology. RESULTS: Schizophrenic patients showed lower global mean sensitivity (30,97 ± 2,25 dB) compared with controls (32,17 ± 3,08 dB), p<0.009. Although there was no difference in the delta sensitivity of hemispheres, there was a difference in sensitivity analysis of the fibers crossing the optic chiasm, with lower mean sensitivity in the patient group (28,80 dB) versus controls (30,66 dB). The difference was higher in fibers that do not cross the optic chiasm, with lower mean sensitivity in patients (27,61 dB) versus controls (30,26 dB), p<0.005. CONCLUSIONS: Our results suggest that there are differences between global sensitivity and fiber sensitivity measured by frequency doubling technology. The different sensitivity of fibers that do not cross the optic chiasm is consistent with most current etiological hypotheses for schizophrenia. The decreased sensitivity responses in the optic radiations may significantly contribute to research assessing early-stage visual processing deficits for patients with schizophrenia.

HISTÓRICO: Déficits de processamento visual foram relatados em pacientes com esquizofrenia. Estudos anteriores demonstraram diferenças no estágio inicial de processamento de esquizofrênicos, embora a natureza, extensão e localização do distúrbio são desconhecidas. As vias magnocelulares e parvocelular visuais são associados com canais transitórios e sustentado, mas suas respectivas contribuições para a esquizofrenia relacionados com déficits visuais permanece controverso. OBJETIVO: Avaliar a disfunção magnocelular na esquizofrenia usando a tecnologia de frequência dupla. MÉTODOS: Trinta e um pacientes com esquizofrenia e 34 voluntários saudáveis ​​foram examinados. Tecnologia de frequência dupla foi realizada em uma sessão, consistindo de uma estratégia de rastreio de 15 minutos, seguido do programa de C-20 para tecnologia de frequência dupla. RESULTADOS: Os pacientes esquizofrênicos apresentaram sensibilidade média inferior global (30,97 ± 2,25 dB), em comparação com os controles (32,17 ± 3,08 dB), p<0,009. Embora não tenha ocorrido diferença na sensibilidade do delta de hemisférios, houve uma diferença na análise de sensibilidade das fibras que atravessam a quiasma, com menor sensibilidade média no grupo de pacientes (28,80 dB) versus controlos (30,66 dB). A diferença foi maior em fibras que não cruzam o quiasma óptico, com menor sensibilidade média em pacientes (27,61 dB) versus controles (30,26 dB), p<0,005. CONCLUSÕES: Nossos resultados sugerem que há diferenças entre a sensibilidade global e sensibilidade da fibra medida pela tecnologia de frequência dupla. A sensibilidade diferente de fibras que não cruzam o quiasma óptico é compatível com a maioria das atuais hipóteses etiológicas para a esquizofrenia. As respostas diminuição da sensibilidade nas radiações ópticas podem contribuir significativamente para pesquisar a avaliação em estágio inicial déficits de processamento visual em pacientes com esquizofrenia.

Color vision versus pattern visual evoked potentials in the assessment of subclinical optic pathway involvement in multiple sclerosis.

BACKGROUND: Optic pathway involvement in multiple sclerosis is frequently the initial sign in the disease process. In most clinical applications, pattern visual evoked potential (PVEP) is used in the assessment of optic pathway involvement. OBJECTIVE: To question the value of PVEP against color vision assessment in the diagnosis of subclinical optic pathway involvement. MATERIALS AND METHODS: This prospective, cross-sectional study included 20 multiple sclerosis patients without a history of optic neuritis, and 20 healthy control subjects. Farnsworth-Munsell (FM) 100-Hue testing and PVEPs to 60-min arc and 15-min arc checks by using Roland-Consult RetiScan® system were performed. P 100 amplitude, P 100 latency in PVEP and total error scores (TES) in FM 100-Hue test were assessed. RESULTS: Expanded Disability Status Scale score and the time from diagnosis were 2.21 ± 2.53 (ranging from 0 to 7) and 4.1 ± 4.4 years. MS group showed significantly delayed P 100 latency for both checks (P < 0.001). Similarly, MS patients had significantly increased total error scores (TES) in FM-100 Hue (P < 0.001). The correlations between TESs and PVEP amplitudes / latencies were insignificant for both checks (P > 0.05 for all). 14 MS patients (70%) had an increased TESs in FM-100 Hue, 11 (55%) MS patients had delayed P 100 latency and 9 (45%) had reduced P 100 amplitude. The areas under the ROC curves were 0.944 for FM-100 Hue test, 0.753 for P 100 latency, and 0.173 for P 100 amplitude. CONCLUSIONS: Color vision testing seems to be more sensitive than PVEP in detecting subclinical visual pathway involvement in MS.

Late ophthalmological assessment of patients with subarachnoid hemorrhage and clipping of cerebral aneurysm.

PURPOSE: To estimate prospectively late ocular manifestations in patients after aneurysmal subarachnoid hemorrhage (SAH) treated with aneurysm clipping. METHODS: Forty-six patients (12 men and 34 women), 23-69 years of age, were included in this study. A conventional ophthalmological examination, visual evoked potentials (VEPs), and static perimetry were performed on all patients. The mean interval between the onset of SAH and the aforementioned examination was 1.9 ± 1.3 years (range 0.5-5 years). The following were compared between patients with affected and non-affected visual fields as well as between those with normal and abnormal VEPs: sex, age, time from SAH to surgery, Hunt and Hess scale, Glasgow Coma Scale, Glasgow Outcome Scale, grading of SAH according to the Fisher scale, and the size and site of aneurysm. RESULTS: Visual field defects were found in 23 patients (50%). In all of these patients, both eyes were affected. The most frequent type of visual field defects were: constricted field (47.8%), multiple peripheral foci (26.1%), and superior field defect (17.4%). There was no significant relationship between the analyzed factors and the occurrence of visual field defects, although statistical significance was almost observed in respect to the Fisher scale (p = 0.055). Deterioration in VEPs was observed in nine patients (19.6%). In the group of patients with abnormal VEPs, the time from onset of SAH to surgery was 2.6 ± 1.8 days, whereas in the group of patients with normal VEPs this time amounted to 6.4 ± 2.4 days (p = 0.02). In patients with no changes in VEPs, the mean Fisher score was significantly higher than in the group with abnormal VEPs (2.8 ± 0.6 vs 2.0 ± 0.4 respectively, p = 0.04). CONCLUSION: Visual field defects and VEP deterioration are frequent late ocular manifestations of SAH treated with aneurysm clipping. Damage to the visual pathway correlates with the severity of SAH and timing of aneurysmal surgery.

Steady state responses: electrophysiological assessment of sensory function in schizophrenia.

Persons with schizophrenia experience subjective sensory anomalies and objective deficits on assessment of sensory function. Such deficits could be produced by abnormal signaling in the sensory pathways and sensory cortex or later stage disturbances in cognitive processing of such inputs. Steady state responses (SSRs) provide a noninvasive method to test the integrity of sensory pathways and oscillatory responses in schizophrenia with minimal task demands. SSRs are electrophysiological responses entrained to the frequency and phase of a periodic stimulus. Patients with schizophrenia exhibit pronounced auditory SSR deficits within the gamma frequency range (35-50 Hz) in response to click trains and amplitude-modulated tones. Visual SSR deficits are also observed, most prominently in the alpha and beta frequency ranges (7-30 Hz) in response to high-contrast, high-luminance stimuli. Visual SSR studies that have used the psychophysical properties of a stimulus to target specific visual pathways predominantly report magnocellular-based deficits in those with schizophrenia. Disruption of both auditory and visual SSRs in schizophrenia are consistent with neuropathological and magnetic resonance imaging evidence of anatomic abnormalities affecting the auditory and visual cortices. Computational models suggest that auditory SSR abnormalities at gamma frequencies could be secondary to gamma-aminobutyric acid-mediated or N-methyl-D-aspartic acid dysregulation. The pathophysiological process in schizophrenia encompasses sensory processing that probably contributes to alterations in subsequent encoding and cognitive processing. The developmental evolution of these abnormalities remains to be characterized.

Assessment of NMDA receptor NR1 subunit hypofunction in mice as a model for schizophrenia.

N-methyl-D-aspartate receptors (NMDARs) play a pivotal role in excitatory neurotransmission, synaptic plasticity and brain development. Clinical and experimental evidence suggests a dysregulation of NMDAR function and glutamatergic pathways in the pathophysiology of schizophrenia. We evaluated electrophysiological and behavioral properties of NMDAR deficiency utilizing mice that express only 5-10% of the normal level of NMDAR NR1 subunit. Auditory and visual event related potentials yielded significantly increased amplitudes for the P20 and N40 components in NMDAR deficient (NR1(neo)-/-) mice suggesting decreased inhibitory tone. Compared to wild types, NR1(neo)-/- mice spent less time in social interactions and showed reduced nest building. NR1(neo)-/- mice displayed a preference for open arms of a zero maze and central zone of an open field, possibly reflecting decreased anxiety-related behavioral inhibition. However, locomotor activity did not differ between groups in either home cage environment or during behavioral testing. NR1(neo)-/- mice displayed hyperactivity only when placed in a large unfamiliar environment, suggesting that neither increased anxiety nor non-specific motor activation accounts for differential behavioral patterns. Data suggest that NMDAR NR1 deficiency causes disinhibition in sensory processing as well as reduced behavioral inhibition and impaired social interactions. The behavioral signature in NR1(neo)-/- mice supports the impact of impaired NMDAR function in a mouse model with possible relevance to negative symptoms in schizophrenia.

Electrodiagnostic assessment in optic nerve disease.

PURPOSE OF REVIEW: Complementary electrophysiological techniques can be useful in detecting and localizing dysfunction within the visual pathway. Recent developments are outlined in the context of neuro-ophthalmology. RECENT FINDINGS: The relationship between nerve fibre layer anatomy and the pattern visual evoked potential has been addressed, correlating axonal loss with visual pathway dysfunction. Longitudinal assessment of multiple sclerosis patients has defined parameters affecting the utility of the pattern visual evoked potential as an outcome measure in potential treatment trials. In optic nerve tumours, the pattern visual evoked potential may help identify and monitor the disorder. The pattern electroretinogram assesses retinal ganglion cell function and can identify macular dysfunction, possibly mimicking optic nerve disease clinically. The spatial extent of macular dysfunction can be assessed using the multifocal electroretinogram. Objective visual evoked potential assessment of visual acuity can be important in the management of nonorganic visual loss. The multifocal visual evoked potential is a relatively new technique that is attracting increasing research interest, particularly as a measure of visual field loss, but has yet to be established as a reliable diagnostic tool. SUMMARY: Electrophysiology, combined with clinical and imaging investigations, is a powerful diagnostic and monitoring tool. Macular dysfunction can mimic optic nerve disease in the absence of fundus abnormality.

Electrophysiological assessment of visual function in patients with non-arteritic ischaemic optic neuropathy.

BACKGROUND AND PURPOSE: Our study aims to evaluate retinal function and neural conduction in post-retinal visual pathways of patients with non-arteritic ischaemic optic neuropathy (NION). METHODS: Twenty patients (mean age: 63.7 +/- 5.96 year) with NION and 20 age-similar control subjects were enrolled. Simultaneous recording of pattern electroretinograms (PERGs) and visual evoked potentials (VEPs), and Log of minimum angle resolution (MAR) visual acuity (VA) were assessed in NION patients and controls. RESULTS: Significantly (ANOVA, P < 0.01) abnormal PERG and VEP responses, delayed retinocortical time (RCT, difference between VEP P100 and PERG P50 implicit times), and reduced VA were found in NION patients with respect to control subjects. The delay in RCT was not significantly (Pearson's test, P > 0.01) correlated with the PERG impairment. The reduction in VA was significantly (Pearson's test, P < 0.01) correlated to the increase in VEP P100 implicit time and RCT, whereas no correlations (P > 0.01) were found with PERG abnormalities. CONCLUSIONS: Non-arteritic ischaemic optic neuropathy patients with a reduction in VA may present two different, unrelated impairments: a dysfunction of the inner retinal layer (abnormal PERG) and abnormal post-retinal neural conduction (abnormal VEP and RCT). The reduction in VA seems to be related to the post-retinal impairment and seems to be independent from the retinal dysfunction.

Assessment of contrast gain signature in inferred magnocellular and parvocellular pathways in patients with glaucoma.

PURPOSE: Contrast gain signatures of inferred magnocellular and parvocellular postreceptoral pathways were assessed for patients with glaucoma using a contrast discrimination paradigm developed by Pokorny and Smith. The potential causes for changes in contrast gain signature were investigated using model simulations of ganglion cell contrast responses. METHODS: Foveal contrast discrimination thresholds were measured with a pedestal-Delta-pedestal paradigm developed by Pokorny and Smith [Pokorny, J., & Smith, V. C. (1997). Psychophysical signatures associated with magnocellular and parvocellular pathway contrast gain. Journal of the Optical Society of America A, 14(9), 2477-2486]. Stimuli were 27 ms luminance increments superimposed on 227 ms pulsed Delta-pedestals. Contrast thresholds and contrast gain signatures mediated by the inferred magnocellular (MC) and parvocellular (PC) pathways were assessed using linear fits to contrast discrimination thresholds at either lower or higher Delta-pedestal contrasts, respectively. Twenty-seven patients with glaucoma were tested, as well as 16 age-similar control subjects free of eye disease. RESULTS: Contrast sensitivity and contrast gain signature mediated by the inferred MC pathway were lower for the glaucoma group, and reduced contrast gain signature was correlated with reduced contrast sensitivity (r(2)=45%, p<.0005). These two parameters mediated by the inferred PC pathway were little affected for the glaucoma group. Model simulations suggest that the reduced contrast sensitivity and contrast gain signature were consistent with the hypothesis that reduced MC ganglion cell dendritic complexity can lead to reduced effective retinal illuminance, and hence increased semi-saturation contrast of the ganglion cell contrast response functions. CONCLUSIONS: The contrast sensitivity and contrast gain signature of the inferred MC pathway were reduced in patients with glaucoma. The results were consistent with a model of ganglion cell dysfunction due to reduced synaptic density.

Longitudinal quantitative assessment of vision function in children with cortical visual impairment.

PURPOSE: Cortical visual impairment (CVI) is bilateral visual impairment caused by damage to the posterior visual pathway, the visual cortex, or both. Current literature reports great variability in the prognosis of CVI. The purpose of this study was to evaluate change in vision function in children with CVI over time using a quantitative assessment method. METHODS: The visual acuity and contrast sensitivity of children with CVI were retrospectively assessed using the sweep visual evoked potential (VEP). Thirty-nine children participated in the visual acuity assessment and 34 of the 39 children participated in the contrast threshold assessment. At the time of the first VEP, the children ranged in age from 1 to 16 years (mean: 5.0 years). The time between measures ranged from 0.6 to 13.7 years (mean: 6.5 years). RESULTS: Forty-nine percent of the children studied showed significant improvement of visual acuity. The average improvement was 0.43 log unit (mean change: 20/205 to 20/76) in those who improved. The initial visual acuity was worse in those who improved compared with those who did not improve (p < 0.001). Forty-seven percent of the children studied showed significant improvement of contrast threshold. In those who improved, the average amount of improvement was 0.57 log unit (10 to 2.6% Michelson). The initial contrast threshold was significantly worse in those who improved compared with those who did not improve (p = 0.001). Also, the change in contrast threshold was related to age of the child (p = 0.017). CONCLUSIONS: Significant improvement in vision function can occur over time in children with CVI. In the present study, approximately 50% of the children improved and the remainder remained stable. No relation was found between etiology and improvement. Further investigation is warranted to better understand the prognosis for visual recovery in children with CVI.

Assessment of patients with suspected non-organic visual loss using pattern appearance visual evoked potentials.

BACKGROUND: The aim of the study was to validate the use of the short duration pattern onset visual evoked potential (PappVEP) in the objective assessment of visual acuity (VA) in patients referred with presumed non-organic visual loss. METHODS: The combination of minimum check size and minimum contrast required to elicit a consistently discernible PappVEP (amplitude >or=5 microV) were measured in ten normal subjects under conditions of induced optical blur (0 to +3 dioptres) and the relationship to Snellen VA established. The data from 100 consecutive patients (167 eyes) referred for possible non-organic visual loss (NOVL) and 20 patients with confirmed visual pathway dysfunction were reviewed in relation to the results in normal subjects. RESULTS: Snellen VA, under conditions of blur, could be predicted in normal subjects from the check size and contrast required to elicit a criterion PappVEP. These data were tabulated and a quantitative guideline established for the estimation of VA in the patients referred with suspected NOVL. Most (88%) patients referred with suspected NOVL had normal electrophysiology and PappVEPs consistent with normal Snellen VA. In others, they suggested a degree of non-organic overlay. In 20 cases of organic visual loss, PappVEPs were in close agreement with subjective VA. CONCLUSIONS: The short duration pattern onset visual-evoked potential is confirmed as a clinically useful tool in the objective assessment of patients with suspected non-organic visual loss.