Visual evoked potentials under luminance contrast and color contrast stimulation in glaucoma diagnosis

Chromatic visual evoked potentials: A review of physiology, methods and clinical applications

Objective assessment of the visual system can be performed electrophysiologically using the visual evoked potential (VEP). In many clinical circumstances, this is performed using high contrast achromatic patterns or diffuse flash stimuli. These methods are clinically valuable but they may only assess a subset of possible physiological circuitries within the visual system, particularly those involved in achromatic (luminance) processing. The use of chromatic VEPs (cVEPs) in addition to standard VEPs can inform us of the function or dysfunction of chromatic pathways. The chromatic VEP has been well studied in human health and disease. Yet, to date our knowledge of their underlying mechanisms and applications remains limited. This likely reflects a heterogeneity in the methodology, analysis and conclusions of different works, which leads to ambiguity in their clinical use. This review sought to identify the primary methodologies employed for recording cVEPs. Furthermore cVEP maturation and application in understanding the function of the chromatic system under healthy and diseased conditions are reviewed. We first briefly describe the physiology of normal colour vision, before describing the methodologies and historical developments which have led to our understanding of cVEPs. We thereafter describe the expected maturation of the cVEP, followed by reviewing their application in several disorders: congenital colour vision deficiencies, retinal disease, glaucoma, optic nerve and neurological disorders, diabetes, amblyopia and dyslexia. We finalise the review with recommendations for testing and future directions.

Pattern electroretinogram, blue-yellow visual evoked potentials and the risk of developing visual field defects in glaucoma suspects: a longitudinal "survival" analysis with a very long follow-up

PURPOSE

Estimating glaucoma suspects' risk for visual field defects helps to avoid under- and over-treatment. In this retrospective, longitudinal cohort study with a very long follow-up, we studied whether pattern electroretinograms (PERG) amplitudes and blue-on-yellow visual evoked potential (BY-VEP) latencies can predict visual field defects.

METHODS

Participants of the Erlangen Glaucoma Study were examined with PERG and BY-VEP between 9/1991 and 8/2001. Stimuli were created using an optical bench with Maxwellian view and consisted of vertical gratings (0,88 cpd) in a 32° field for both PERG and BY-VEP. Patients were treated according to clinical standards and performed standard automated perimetry (SAP) annually. Retrospectively, patients with normal SAP at baseline were selected. Primary endpoint was conversion to perimetric glaucoma. Predictive value was modeled using Kaplan-Meier analyses and a multivariate cox proportional hazards model with the continuous variables PERG amplitude, BY-VEP peak time and SAP square-root of loss variance (sLV) after stratification for Jonas classification of the optic discs.

RESULTS

Of 412 patients (288: Jonas 0, 103: I, and 21: II; baseline age: 20-60 years), 65 converted to perimetric glaucoma during follow-up (0.5-23.3 years; median 5.5 years). Optic disc classification was a strong risk factor for conversion (log rank p < 0.0001), and patients with more advanced changes progressed earlier. In the multivariate analysis (log rank p = 0.005), only PERG amplitude remained an independent risk factor after stratification for optic disc morphology (p = 0.021), with a ~ 30% higher risk per μV amplitude decrease.

CONCLUSIONS

PERG helps to estimate glaucoma suspects' risk for visual field defects.

Blue-Yellow VEP with Projector-Stimulation in Glaucoma

Background and aim

In the past, increased latencies of the blue-on-yellow pattern visually evoked potentials (BY-VEP), which predominantly originate in the koniocellular pathway, have proven to be a sensitive biomarker for early glaucoma. However, a complex experimental setup based on an optical bench was necessary to obtain these measurements because computer screens lack sufficient temporal, spatial, spectral, and luminance resolution. Here, we evaluated the diagnostic value of a novel setup based on a commercially available video projector.

Methods

BY-VEPs were recorded in 126 participants (42 healthy control participants, 12 patients with ocular hypertension, 17 with “preperimetric” glaucoma, and 55 with perimetric glaucoma). Stimuli were created with a video projector (DLP technology) by rear projection of a blue checkerboard pattern (460 nm) for 200 ms (onset) superimposed on a bright yellow background (574 nm), followed by an offset interval where only the background was active. Thus, predominantly S-cones were stimulated while L- and M-cone responses were suppressed by light adaptation. Times of stimulus onset to VEP onset-trough (N-peak time) and offset-peak (P-peak time) were analyzed after age-correction based on linear regression in the normal participants.

Results

The resulting BY-VEPs were quite similar to those obtained in the past with the optical bench: pattern-onset generated a negative deflection of the VEP, whereas the offset-response was dominated by a positive component. N-peak times were significantly increased in glaucoma patients (preperimetric 136.1 ± 10 ms, p < 0.05; perimetric 153.1 ± 17.8 ms, p < 0.001) compared with normal participants (123.6 ± 7.7 ms). Furthermore, they were significantly correlated with disease severity as determined by visual field losses retinal nerve fiber thinning (Spearman R = –0.7, p < 0.001).

Conclusions

Video projectors can be used to create optical stimuli with high temporal and spatial resolution, thus potentially enabling sophisticated electrophysiological measurements in clinical practice. BY-VEPs based on such a projector had a high diagnostic value for detection of early glaucoma.

Registration of study

Registration site: www.clinicaltrials.gov

Trial registration number: NCT00494923.

[The role of citicoline in glaucoma]

Hintergrund

In den letzten Jahren wurde in vielen experimentellen und klinischen Studien gezeigt, dass bei der Glaukomerkrankung die neuronale Degeneration nicht nur auf der Höhe von Netzhaut und Sehnerv, sondern im Verlauf der gesamten Sehbahn und des Gehirns erfolgt.

Fragestellung

Dargestellt werden die neuroprotektive Wirkung und ihre Mechanismen von Citicolin bei der Glaukomerkrankung.

Material und Methode

Vor dem Hintergrund der Neuroanatomie, des Neuroimaging und der Pathogenese der Glaukomerkrankung wird die Relevanz erläutert. Die Daten der experimentellen und klinischen Studien werden dargelegt und ein Fazit für die klinische Anwendung gezogen.

Ergebnisse

Citicolin wirkt neuroprotektiv über glaukomrelevante Mechanismen. Die neuroprotektive Wirkung von Citicolin bei Offenwinkelglaukomen ist funktionell und morphologisch nachweisbar. Sie ist unabhängig vom Glaukomschaden und Augeninnendruck und tritt i. d. R. erst nach einem Jahr auf. Die Effekte von oralem Citicolin treten bei einer Tagesdosis von 500–1000 mg auf. Die Einnahme von Citicolin kann dauerhaft oder in Zyklen erfolgen. In den Studien traten bei der Einnahme von Citicolin keine Nebenwirkungen auf. Citicolin kann kognitive Leistungen und somit Therapieadhärenz sowie die Lebensqualität bei Glaukompatienten verbessern

Schlussfolgerung

Diese relativ alte nootrope Substanz, welche jetzt als Nahrungsergänzungsmittel vertrieben wird, scheint eine wertvolle Ergänzung zur konventionellen Therapie der Glaukomerkrankung und eine rationale Option zur Neuroprotektion und Prophylaxe zu sein.

Pattern Electroretinography and Visual Evoked Potentials Provide Clinical Evidence of CNS Modulation of High- and Low-Contrast VEP Latency in Glaucoma

Purpose

Both pattern electroretinography (PERG) and visual evoked potentials (VEP) can be performed using low- (15%; Lc) and high- (85%; Hc) contrast gratings that may preferentially stimulate the magno- and parvocellular pathways. We observed that among glaucomatous patients showing only one VEP latency deficit per eye, there appeared to be a very strong tendency for an Hc delay in one eye and an Lc delay in the other.

Methods

Diopsys NOVA-LX system was used to measure VEP Hc and Lc latency among a clinical glaucoma population to find all individuals with either a single Hc or Lc latency abnormality in each eye (group 1), or with greater than 0 and less than 4 Hc or Lc VEP latency abnormalities in the two eyes (group 2) to determine whether a significant inverse correlation existed for these values in either group. Hc and Lc PERG data were also evaluated to assess associated retinal ganglion cell responses.

Results

A strong inverse correlation (P = 0.0000003) was observed between the Hc and Lc VEP latency values among the 64 eyes in group 1. Group 2 provided a comparable result (n = 143; 286 eyes; P = 0.0005). PERG (n = 81; 162 eyes) also showed strong bilateral symmetry for magnitude values (P < 0.0001 for both Lc and Hc in groups 1 and 2).

Conclusions

Bilateral retention of both low-resolution/high-speed and high-resolution/low-speed function may persist with both eyes open despite symmetrically pathologic retinal ganglion cell PERG waveform asynchrony for Hc and Lc stimuli in the paired eyes.

Translational Relevance

Clinical electrophysiology strongly suggests binocular compensation for dynamic dysfunction operates under central nervous system (CNS) control in glaucoma.

Development and validation of an associative model for the detection of glaucoma using pupillography

PURPOSE

To develop and validate an associative model using pupillography that best discriminates those with and without glaucoma.

DESIGN

A prospective case-control study.

METHODS

We enrolled 148 patients with glaucoma (mean age 67 ± 11) and 71 controls (mean age 60 ± 10) in a clinical setting. This prototype pupillometer is designed to record and analyze pupillary responses at multiple, controlled stimulus intensities while using varied stimulus patterns and colors. We evaluated three approaches: (1) comparing the responses between the two eyes; (2) comparing responses to stimuli between the superonasal and inferonasal fields within each eye; and (3) calculating the absolute pupil response of each individual eye. Associative models were developed using stepwise regression or forward selection with Akaike information criterion and validated by fivefold cross-validation. We assessed the associative model using sensitivity, specificity and the area-under-the-receiver operating characteristic curve.

RESULTS

Persons with glaucoma had more asymmetric pupil responses in the two eyes (P < 0.001); between superonasal and inferonasal visual field within the same eye (P = 0.014); and smaller amplitudes, slower velocities and longer latencies of pupil responses compared to controls (all P < 0.001). A model including age and these three components resulted in an area-under-the-receiver operating characteristic curve of 0.87 (95% CI 0.83 to 0.92) with 80% sensitivity and specificity in detecting glaucoma. This result remained robust after cross-validation.

CONCLUSIONS

Using pupillography, we were able to discriminate among persons with glaucoma and those with normal eye examinations. With refinement, pupil testing may provide a simple approach for glaucoma screening.

Significance of Visual Evoked Potentials in the Assessment of Visual Field Defects in Primary Open-Angle Glaucoma: A Review

Visual evoked potentials is an important visual electrophysiological tool which has been used for the evaluation of visual field defects in primary open-angle glaucoma and is an appropriate objective measure of optic nerve function. Significant correlations between the magnitude of the VEP parameters and MD of Humphrey static perimetry suggest that the impaired visual cortical responses observed in glaucoma patients can be revealed by both electrophysiological and psychophysical methods. In addition, the severity of global glaucomatous damage evidenced by reduction in MD could depend on the delay in neural conduction from retina to the visual cortex as revealed by the significant correlation between VEP latencies and MD which also supports the validity of the VEP testing in progression of glaucoma.

Identifying preperimetric functional loss in glaucoma: a blue-on-yellow multifocal visual evoked potentials study

PURPOSE

To determine the ability of blue-on-yellow multifocal visual evoked potentials (BonY mfVEP) to identify functional loss in preperimetric glaucoma.

DESIGN

Prospective case series.

PARTICIPANTS

Thirty patients with glaucomatous optic discs and normal standard visual fields.

METHODS

All patients underwent BonY mfVEP, dilated optic disc stereophotography, and optical coherence tomography (Fast RNFL protocol). Optic disc photographs were assessed by 2 independent examiners in a masked fashion.

MAIN OUTCOME MEASURES

The mfVEP amplitude asymmetry and latency values were analyzed and compared topographically with findings of disc assessment. Average retinal nerve fiber layer (RNFL) thickness, RNFL asymmetry, and sectors with RNFL thinning were compared between patients with and without mfVEP defects.

RESULTS

Fourteen (46.7%) patients demonstrated significant abnormality on amplitude asymmetry deviation plots of BonY mfVEP. In all 14 cases, the defect was monocular and corresponded to the eye with the worse disc. In 13 of 14 patients, the defect also corresponded to the location of the worst affected rim. Average RNFL thickness of eyes with mfVEP defects was 81.2+/-9.9 microm, significantly lower than that of patients without defects (90+/-10.5 microm; P = 0.035). Mean asymmetry of RNFL (better minus worse eye) also was significantly higher for patients with mfVEP defects compared with those without such defects (9.0+/-6.4 microm vs. 3.0+/-7 microm; P = 0.03). Average latency of both eyes of glaucomatous patients was delayed compared with that of controls, with no difference in latency between worse and better eyes of glaucoma patients. There was no association of latency delay with either the location of disc changes or mfVEP amplitude defects.

CONCLUSIONS

Amplitude asymmetry of the BonY mfVEP seems to be a promising tool to identify functional loss in preperimetric glaucoma.

FINANCIAL DISCLOSURE(S)

Proprietary or commercial disclosure may be found after the references.

Chromatic modulation of luminance visual evoked potential latencies in healthy subjects and patients with mild vision disorders

OBJECTIVE

To study whether and how color modulates luminance visual evoked potentials (VEPs).

METHODS

We studied pattern-reversal luminance VEPs to red/black and blue/black checkerboards with identical luminance contrast values (mixed luminance and chromatic components) (isocontrast color VEP, in brief, IVEPs) in 25 healthy subjects and two groups of patients with mild vision disorders (23 with glaucoma and 25 with optic neuritis). We then compared these with the standard color VEPs to pure chromatic contrast red/green and blue/yellow gratings (CVEPs).

RESULTS

In healthy subjects, VEPs to red/black checkerboards and red/green gratings were slower than those obtained with blue/black checkerboards and blue/yellow gratings. Both procedures (IVEPs and CVEPs) differentiated patients with vision disorders from healthy subjects and distinguished between the two different vision disorders. Red/black checkerboards and red-green gratings elicited slower VEPs in patients with optic neuritis and blue/black checkerboards and blue/yellow gratings elicited slower VEPs in patients with glaucoma. IVEPs appeared more stable and ample than CVEPs. The contrast indices normalized CVEP and IVEP latencies in the same subject and showed a positive correlation between CVEP and IVEP latencies in healthy subjects and in patients with optic neuritis, but not in patients with glaucoma.

CONCLUSIONS

Our study confirms the usefulness of CVEPs in detecting and differentiating mild vision disorders. IVEPs to colored pattern-reversal luminance checkerboards are equally effective in distinguishing between various vision disorders possibly because colors can modulate VEP latencies to luminance contrast stimuli.

SIGNIFICANCE

IVEPs can be useful in differentiating the various vision disorders and are easier than CVEPs to test in a routine clinical setting.

Multifocal Blue-on-Yellow Visual Evoked Potentials in Early Glaucoma

OBJECTIVE

To determine the sensitivity and specificity of blue-on-yellow multifocal visual evoked potentials (mfVEPs) in early glaucoma.

DESIGN

Cross-sectional study.

PARTICIPANTS

Fifty patients with a confirmed diagnosis of early glaucoma and 60 normal participants.

METHODS

Black-and-white mfVEPs and blue-on-yellow mfVEPs were recorded using the Accumap version 2.0 (ObjectiVision Pty. Ltd., Sydney, Australia). All patients also underwent achromatic standard automated perimetry (SAP).

MAIN OUTCOME MEASURES

Multifocal VEP amplitude and latency values in glaucoma patients were analyzed and compared with those of the normal controls.

RESULTS

Based on the definition of visual field defect, in the group of glaucomatous eyes with SAP defects, amplitude of blue-on-yellow mfVEP was abnormal in all 64 cases (100% sensitivity), whereas black-and-white mfVEP missed 5 cases (92.2% sensitivity). Generally, larger scotomata were noted on blue-on-yellow mfVEP compared with black-and-white mfVEP for the same eyes. There was high topographic correspondence between SAP and amplitude of blue-on-yellow mfVEP and significant (P<0.0001) correlation between them (correlation coefficient, 0.73). Abnormal amplitude was detected in 3 of 60 eyes of control subjects (95% specificity). There was, however, no correlation between visual field defect and latency delay in glaucoma patients. Although there was a significant difference between averaged latency of control and glaucoma eyes, values considerably overlapped.

CONCLUSIONS

The blue-on-yellow mfVEP is a sensitive and specific tool for detecting early glaucoma based on amplitude analysis.

Electrophysiological assessment of glaucomatous visual dysfunction during treatment with cytidine-5'-diphosphocholine (citicoline): a study of 8 years of follow-up

In this study we assessed, by simultaneous recordings of visual evoked potentials (VEPs) and pattern-electroretinograms (PERGs), the effects cytidine-5'-diphosphocholine (citicoline) on retinal function and/or visual cortical responses in glaucoma patients. Thirty glaucoma patients were randomly divided into two age-matched groups: patients in group GC (15 patients) were treated with citicoline (1,000 mg/die intramuscularly) for 2 months; patients in group GP (15 patients) were treated with placebo for 2 months. After 4 months of wash-out (month 6), GC patients underwent a further 2-month period of citicoline treatment (months 7-8) followed by another 4-month period of wash-out (months 9-12). In GP patients the wash-out was extended for a further 6 months (months 7-12). During the following 13-96 months, GC patients received additional 2-month periods of treatment with citicoline (each period followed by 4 months of wash-out) for a total of 16 periods in 8 years. GP patients were also examined at months 24, 26, 48, 60, 72, 84 and 96. In GC patients the first two treatments with citicoline induced a significant (p <0.01) improvement of VEP and PERG parameters with respect to pre-treatment conditions. VEPs and PERGs recorded in GC patients after the first wash-out revealed that, although there was a worsening trend, the electrophysiological improvement was still maintained with respect to baseline conditions. The additional periods of citicoline treatment in GC patients during the subsequent 13-96 months induced a greater (p <0.01) improvement of VEP and PERG parameters with respect to pre-treatment conditions and when compared to GP patients. Thus, we observed that citicoline significantly improves retinal and cortical bioelectrical responses in glaucoma patients, suggesting a potential use of this substance in the medical treatment of glaucoma, as a complement to hypotensive therapy.

Stereoscopic visual evoked potentials in normal subjects and patients with open-angle glaucomas

PURPOSE

To evaluate stereoscopic visual evoked potentials (S-VEP) in normal controls and in patients with glaucomatous optic nerve damage.

METHODS

Computer-generated dynamic random-dot stereograms were used to elicit cortical visual evoked potentials using wireless electric liquid crystal shutter glasses. Normal subjects (n=22) and patients with glaucoma (n=22) were investigated using five different disparities from 9 to 40 arc min. Statistical dependency of measurements with different stimulus at identical patients was adjusted for.

RESULTS

Peak times of onset and offset response of S-VEP can be significantly delayed in glaucomas. A general linear regression model confirmed that differences between patients and normals depend on disparity. S-VEP onset shows no significant difference between controls and glaucomas at 9 arc min disparity. At high disparities, however, peak time of the onset response was significantly (p<0.01) delayed in glaucomas when compared with normals (normals: 125.8+/-13 ms, glaucomas: 148.2+/-25.6 ms at 40 arc min).

CONCLUSIONS

Visual evoked potential elicited by the onset of a random-dot stereogram can be used for objective measurement of stereoacuity in a clinical setting. Differences between controls and glaucomas in high and low disparities could indicate a stereo-specific deficit in glaucoma.

Cortical OFF-potentials from the S-cone pathway reveal neural damage in early glaucoma

We used background adaptation and silent substitution techniques to record full-field ON and OFF-visually evoked cortical potentials (VECPs) selectively from the S-cone and L- and M-cone pathways in 15 patients with primary open angle glaucoma (POAG), and 15 normal controls. The most statistically significant (P=0.01) VECP test for POAG was a voltage change in the S-cone pathway cortical OFF-response. A sensitivity of 93% was achieved, with 60% specificity at minimum error rate. This is presumed to reflect reduced activity in the S-cone and magnocellular visual pathways, and may provide an effective method for research and monitoring change in early glaucoma.