Multifocal objective perimetry in the detection of glaucomatous field loss

Portable multi-focal visual evoked potential diagnostics for multiple sclerosis/optic neuritis patients

PURPOSE

Multiple sclerosis (MS) is a neuro-inflammatory disease affecting the central nervous system (CNS), where the immune system targets and damages the protective myelin sheath surrounding nerve fibers, inhibiting axonal signal transmission. Demyelinating optic neuritis (ON), a common MS symptom, involves optic nerve damage. We've developed NeuroVEP, a portable, wireless diagnostic system that delivers visual stimuli through a smartphone in a headset and measures evoked potentials at the visual cortex from the scalp using custom electroencephalography electrodes.

METHODS

Subject vision is evaluated using a short 2.5-min full-field visual evoked potentials (ffVEP) test, followed by a 12.5-min multifocal VEP (mfVEP) test. The ffVEP evaluates the integrity of the visual pathway by analyzing the P100 component from each eye, while the mfVEP evaluates 36 individual regions of the visual field for abnormalities. Extensive signal processing, feature extraction methods, and machine learning algorithms were explored for analyzing the mfVEPs. Key metrics from patients' ffVEP results were statistically evaluated against data collected from a group of subjects with normal vision. Custom visual stimuli with simulated defects were used to validate the mfVEP results which yielded 91% accuracy of classification.

RESULTS

20 subjects, 10 controls and 10 with MS and/or ON were tested with the NeuroVEP device and a standard-of-care (SOC) VEP testing device which delivers only ffVEP stimuli. In 91% of the cases, the ffVEP results agreed between NeuroVEP and SOC device. Where available, the NeuroVEP mfVEP results were in good agreement with Humphrey Automated Perimetry visual field analysis. The lesion locations deduced from the mfVEP data were consistent with Magnetic Resonance Imaging and Optical Coherence Tomography findings.

CONCLUSION

This pilot study indicates that NeuroVEP has the potential to be a reliable, portable, and objective diagnostic device for electrophysiology and visual field analysis for neuro-visual disorders.

Visual Field Tests: A Narrative Review of Different Perimetric Methods

Visual field (VF) testing dates back to fifth century B.C. It plays a pivotal role in the diagnosis, management, and prognosis of retinal and neurological diseases. This review summarizes each of the different VF tests and perimetric methods, including the advantages and disadvantages and adherence to the desired standard diagnostic criteria. The review targets beginners and eye care professionals and includes history and evolution, qualitative and quantitative tests, and subjective and objective perimetric methods. VF testing methods have evolved in terms of technique, precision, user-friendliness, and accuracy. Consequently, some earlier perimetric techniques, often still effective, are not used or have been forgotten. Newer technologies may not always be advantageous because of higher costs, and they may not achieve the desired sensitivity and specificity. VF testing is most often used in glaucoma and neurological diseases, but new objective methods that also measure response latencies are emerging for the management of retinal diseases. Given the varied perimetric methods available, clinicians are advised to select appropriate methods to suit their needs and target disease and to decide on applying simple vs. complex tests or between using subjective and objective methods. Newer, rapid, non-contact, objective methods may provide improved patient satisfaction and allow for the testing of children and the infirm.

Objective detection of visual field defects with multifrequency VEPs

PURPOSE

To correlate multifrequency pattern reversal VEPs in quadrants (QmfrVEPs) with perimetric field losses for objective detection of visual field losses.

METHODS

QmfrVEP measurements were performed using four LED-based checkerboard stimulators to stimulate the four quadrants of the visual field. QmfrVEPs were measured monocularly in 5 normal subjects and in 5 glaucoma patients who showed losses in conventional Octopus perimetry. The pattern reversal frequency varied slightly between the stimulators: (11.92, 12.00, 12.08 and 12.16 reversals/sec). The responses to the different stimuli were identified by discrete Fourier analysis. VEPs were recorded using different electrode configurations, and the recording with the highest signal-to-noise ratio (SNR) was used for further analysis.

RESULTS

QmfrVEP responses from the different quadrants can be reliably measured and separated using the 0.08 reversals/sec interstimulus reversal frequency differences. The signal-to-noise ratio in the four quadrants was significantly correlated with the equivalent visual field losses obtained with perimetry (Spearman rank correlation: P < 0.001). In the five glaucoma patients, the SNR was reduced in 15 out of the 16 quadrants with a perimetric defect, in comparison to the results in quadrants of healthy subjects. This confirms the sensitivity of the procedure.

CONCLUSION

QmfrVEP responses can be measured reliably. This pilot study suggests that high SNR values exclude visual field defects and that focal defects can be identified in glaucoma patients.

TRIAL REGISTRATION

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CLINICALTRIALS

gov . NCT00494923.

Portable Multi-focal Visual Evoked Potential Diagnostics for Multiple Sclerosis/Optic Neuritis patients

Purpose

Multiple Sclerosis (MS) is a neuro-inflammatory disease of the Central Nervous System (CNS) in which the body's immune system attacks and destroys myelin sheath that protects nerve fibers and causes disruption in axonal signal transmission. Demyelinating Optic Neuritis (ON) is often a manifestation of MS and involves inflammation of the optic nerve. ON can cause vision loss, pain and discomfort in the eyes, and difficulties in color perception.In this study, we developed NeuroVEP, a portable, wireless diagnostic system that delivers visual stimuli through a smartphone in a headset and measures evoked potentials at the visual cortex from near the O1, Oz, O2, O9 and O10 locations on the scalp (extended 10-20 system) using custom electroencephalography (EEG) electrodes.

Methods

Each test session is constituted by a short 2.5-minute full-field visual evoked potentials (ffVEP) test, followed by a 12.5-minute multifocal VEP (mfVEP) test. The ffVEP test evaluates the integrity of the visual pathway by analyzing the P1 (also known as P100) component of responses from each eye, while the mfVEP test evaluates 36 individual regions of the visual field for abnormalities. Extensive signal processing, feature extraction methods, and machine learning algorithms were explored for analyzing the mfVEP responses. The results of the ffVEP test for patients were evaluated against normative data collected from a group of subjects with normal vision. Custom visual stimuli with simulated defects were used to validate the mfVEP results which yielded 91% accuracy of classification.

Results

20 subjects, 10 controls and 10 with MS and/or ON were tested with the NeuroVEP device and a standard-of-care (SOC) VEP testing device which delivers only ffVEP stimuli. In 91% of the cases, the ffVEP results agreed between NeuroVEP and SOC device. Where available, the NeuroVEP mfVEP results were in good agreement with Humphrey Automated Perimetry visual field analysis. The lesion locations deduced from the mfVEP data were consistent with Magnetic Resonance Imaging (MRI) and Optical Coherence Tomography (OCT) findings.

Conclusion

This pilot study indicates that NeuroVEP has the potential to be a reliable, portable, and objective diagnostic device for electrophysiology and visual field analysis for neuro-visual disorders.

Visual Evoked Potentials for the Detection of Diabetic Retinal Neuropathy

Visual evoked potentials (VEP) are visually evoked signals that extract electroencephalographic activity in the visual cortex that can detect retinal ganglion cells, optic nerves, chiasmal and retrochiasmal dysfunction, including optic radiations, and the occipital cortex. Because diabetes causes diabetic retinopathy due to microangiopathy and neuropathy due to metabolic abnormalities and intraneural blood flow disorders, assessment of diabetic visual pathway impairment using VEP has been attempted. In this review, evidence on the attempts to assess the visual pathway dysfunction due to abnormal blood glucose levels using VEP is presented. Previous studies have provided significant evidence that VEP can functionally detect antecedent neuropathy before fundus examination. The detailed correlations between VEP waveforms and disease duration, HbA1c, glycemic control, and short-term increases and decreases in blood glucose levels are evaluated. VEP may be useful for predicting postoperative prognosis and evaluating visual function before surgery for diabetic retinopathy. Further controlled studies with larger cohorts are needed to establish a more detailed relationship between diabetes mellitus and VEP.

Multifocal Visual Evoked Potentials (mfVEP) for the Detection of Visual Field Defects in Glaucoma: Systematic Review and Meta-Analysis

Some discrepancies have been observed in the diagnostic efficacy of multifocal visual evoked potential (mfVEP) when evaluating visual field defects in glaucoma patients. Therefore, we evaluated the diagnostic precision of the mfVEP in glaucoma to find its best diagnostic indicator. A systematic review and meta-analysis of quantitative studies published up to 1 April 2021 was performed. The methodological quality of the included articles was assessed. Publication bias analysis and heterogeneity tests were performed. The sensitivity, specificity and diagnostic odds ratio were calculated. The area under the curve (AUC) was calculated using the summary of receiver operating characteristics curve. Six studies with a total of 241 patients were included according to the inclusion and exclusion criteria. The AUC was 0.98. There was no evidence of publication bias or threshold effect. The pooled sensitivity and pooled specificity of the mfVEP amplitude for detection of visual field defects in all studies was 0.93 and 0.89, respectively. The positive and negative likelihood ratios of mfVEP amplitude were 6.56 and 0.08, respectively. The amplitude of mfVEP showed a good diagnostic precision in the prediction of visual field defects. Interocular mfVEP amplitude analysis can be a good diagnostic indicator for visual field study.

Visual Evoked Potentials as a Biomarker in Multiple Sclerosis and Associated Optic Neuritis

: ABSTRACT:: Multiple sclerosis (MS) is an inflammatory, degenerative disease of the central nervous system (CNS) characterized by progressive neurological decline over time. The need for better "biomarkers" to more precisely capture and track the effects of demyelination, remyelination, and associated neuroaxonal injury is a well-recognized challenge in the field of MS. To this end, visual evoked potentials (VEPs) have a role in assessing the extent of demyelination along the optic nerve, as a functionally eloquent CNS region. Moreover, VEPs testing can be used to predict the extent of recovery after optic neuritis (ON) and capture disabling effects of clinical and subclinical demyelination events in the afferent visual pathway. In this review, the evolving role of VEPs in the diagnosis of patients with ON and MS and the utility of VEPs testing in determining therapeutic benefits of emerging MS treatments is discussed.

Monitoring of optic nerve function in Neurofibromatosis 2 children with optic nerve sheath meningiomas using multifocal visual evoked potentials

Monitoring optic nerve sheath meningiomas (ONSM) in Neurofibromatosis type 2 (NF2) patients remains difficult. Other ocular manifestations of NF2 may obscure ophthalmic assessment of optic nerve function in these patients. Serial magnetic resonance imaging (MRI) used to assess the optic nerve is not without limitations, being expensive and often requiring general anaesthetic in children, with associated risks. This study was undertaken to describe the use of multifocal visual evoked potentials (multifocal VEP, mfVEP) in the regular monitoring of NF2 patients with ONSM. This study involved three NF2 patients with ONSM who undertook mfVEP testing at an academic ophthalmic centre. Same day mfVEP and routine ophthalmic testing were undertaken. Topographical function of the optic nerve was assessed, utilising tools such as asymmetry deviation and accumap severity index. Results were assessed alongside MRI and visual acuity (VA). From the three patients, five eyes had ONSMs, of which two caused unilateral blindness. The remaining three affected eyes had initial VAs 6/6, 6/24, and 6/18. Over follow up, ranging from 5 to 12 years, all tumours progressed, and VA declined for all patients. Multifocal VEP detected optic nerve functional loss corresponding with visual decline. This case series suggests mfVEP is effective in the objective topographic monitoring of optic nerve function in NF2 patients with ONSM. Due also to its safety in a paediatric population, the test may be considered in the routine monitoring of these patients, to be used to assist regular ophthalmic review and MRI scans.

Detecting Glaucoma With a Portable Brain-Computer Interface for Objective Assessment of Visual Function Loss

Importance

The current assessment of visual field loss in diseases such as glaucoma is affected by the subjectivity of patient responses and the lack of portability of standard perimeters.

Objective

To describe the development and initial validation of a portable brain-computer interface (BCI) for objectively assessing visual function loss.

Design, Setting, and Participants

This case-control study involved 62 eyes of 33 patients with glaucoma and 30 eyes of 17 healthy participants. Glaucoma was diagnosed based on a masked grading of optic disc stereophotographs. All participants underwent testing with a BCI device and standard automated perimetry (SAP) within 3 months. The BCI device integrates wearable, wireless, dry electroencephalogram and electrooculogram systems and a cellphone-based head-mounted display to enable the detection of multifocal steady state visual-evoked potentials associated with visual field stimulation. The performances of global and sectoral multifocal steady state visual-evoked potentials metrics to discriminate glaucomatous from healthy eyes were compared with global and sectoral SAP parameters. The repeatability of the BCI device measurements was assessed by collecting results of repeated testing in 20 eyes of 10 participants with glaucoma for 3 sessions of measurements separated by weekly intervals.

Main Outcomes and Measures

Receiver operating characteristic curves summarizing diagnostic accuracy. Intraclass correlation coefficients and coefficients of variation for assessing repeatability.

Results

Among the 33 participants with glaucoma, 19 (58%) were white, 12 (36%) were black, and 2 (6%) were Asian, while among the 17 participants with healthy eyes, 9 (53%) were white, 8 (47%) were black, and none were Asian. The receiver operating characteristic curve area for the global BCI multifocal steady state visual-evoked potentials parameter was 0.92 (95% CI, 0.86-0.96), which was larger than for SAP mean deviation (area under the curve, 0.81; 95% CI, 0.72-0.90), SAP mean sensitivity (area under the curve, 0.80; 95% CI, 0.69-0.88; P = .03), and SAP pattern standard deviation (area under the curve, 0.77; 95% CI, 0.66-0.87; P = .01). No statistically significant differences were seen for the sectoral measurements between the BCI and SAP. Intraclass coefficients for global and sectoral parameters ranged from 0.74 to 0.92, and mean coefficients of variation ranged from 3.03% to 7.45%.

Conclusions and Relevance

The BCI device may be useful for assessing the electrical brain responses associated with visual field stimulation. The device discriminated eyes with glaucomatous neuropathy from healthy eyes in a clinically based setting. Further studies should investigate the feasibility of the BCI device for home-based testing as well as for detecting visual function loss over time.

Frequency-doubling technology perimetry and multifocal visual evoked potential in glaucoma, suspected glaucoma, and control patients

INTRODUCTION

The gold standard in functional glaucoma evaluation is standard automated perimetry (SAP). However, SAP depends on the reliability of the patients' responses and other external factors; therefore, other technologies have been developed for earlier detection of visual field changes in glaucoma patients. The frequency-doubling perimetry (FDT) is believed to detect glaucoma earlier than SAP. The multifocal visual evoked potential (mfVEP) is an objective test for functional evaluation.

OBJECTIVE

To evaluate the sensitivity and specificity of FDT and mfVEP tests in normal, suspect, and glaucomatous eyes and compare the monocular and interocular mfVEP.

METHODS

Ninety-five eyes from 95 individuals (23 controls, 33 glaucoma suspects, 39 glaucomatous) were enrolled. All participants underwent a full ophthalmic examination, followed by SAP, FDT, and mfVEP tests.

RESULTS

The area under the curve for mean deviation and pattern standard deviation were 0.756 and 0.761, respectively, for FDT, 0.564 and 0.512 for signal and alpha for interocular mfVEP, and 0.568 and 0.538 for signal and alpha for monocular mfVEP. This difference between monocular and interocular mfVEP was not significant.

CONCLUSION

The FDT Matrix was superior to mfVEP in glaucoma detection. The difference between monocular and interocular mfVEP in the diagnosis of glaucoma was not significant.

A frequency-tagging electrophysiological method to identify central and peripheral visual field deficits

BACKGROUND

The aim of this study was to develop a fast and efficient electrophysiological protocol to examine the visual field's integrity, which would be useful in pediatric testing.

METHODS

Steady-state visual-evoked potentials (ssVEPs) to field-specific radial checkerboards flickering at two cycle frequencies (7.5 and 6 Hz for central and peripheral stimulations, respectively) recorded at Oz were collected from 22 participants from 5 to 34 years old and from 5 visually impaired adolescents (12-16 years old). Responses from additional leads (POz, O1, O2), and the impact of gaze deviation on the signals, were also investigated in a subgroup of participants.

RESULTS

Steady-state visual-evoked potentials responses were similar at all electrode sites, although the signal from the central stimulation was significantly higher at Oz and was highly sensitive in detecting gaze deviation. No effect of age or sex was found, indicating similar ssVEP responses between adults and healthy children. Visual acuity was related to the central signal when comparing healthy participants with four central visual impaired adolescents. Clinical validation of our electrophysiological protocol was also achieved in a 15-year-old adolescent with a severe peripheral visual deficit, as assessed with Goldmann perimetry.

CONCLUSIONS

A single electrode over Oz is sufficient to gather both central and peripheral visual signals and also to control for gaze deviation. Our method presents several advantages in evaluating visual fields integrity, as it is fast, reliable, and efficient, and applicable in children as young as 5 years old. However, a larger sample of healthy children should be tested to establish clinical norms.

Evaluation of hemifield sector analysis protocol in multifocal visual evoked potential objective perimetry for the diagnosis and early detection of glaucomatous field defects

Purpose

Multifocal visual evoked potential (mfVEP) is a newly introduced method used for objective visual field assessment. Several analysis protocols have been tested to identify early visual field losses in glaucoma patients using the mfVEP technique, some were successful in detection of field defects, which were comparable to the standard automated perimetry (SAP) visual field assessment, and others were not very informative and needed more adjustment and research work. In this study we implemented a novel analysis approach and evaluated its validity and whether it could be used effectively for early detection of visual field defects in glaucoma.

Methods

Three groups were tested in this study; normal controls (38 eyes), glaucoma patients (36 eyes) and glaucoma suspect patients (38 eyes). All subjects had a two standard Humphrey field analyzer (HFA) test 24-2 and a single mfVEP test undertaken in one session. Analysis of the mfVEP results was done using the new analysis protocol; the hemifield sector analysis (HSA) protocol. Analysis of the HFA was done using the standard grading system.

Results

Analysis of mfVEP results showed that there was a statistically significant difference between the three groups in the mean signal to noise ratio (ANOVA test, p < 0.001 with a 95% confidence interval). The difference between superior and inferior hemispheres in all subjects were statistically significant in the glaucoma patient group in all 11 sectors (t-test, p < 0.001), partially significant in 5 / 11 (t-test, p < 0.01), and no statistical difference in most sectors of the normal group (1 / 11 sectors was significant, t-test, p < 0.9). Sensitivity and specificity of the HSA protocol in detecting glaucoma was 97% and 86%, respectively, and for glaucoma suspect patients the values were 89% and 79%, respectively.

Conclusions

The new HSA protocol used in the mfVEP testing can be applied to detect glaucomatous visual field defects in both glaucoma and glaucoma suspect patients. Using this protocol can provide information about focal visual field differences across the horizontal midline, which can be utilized to differentiate between glaucoma and normal subjects. Sensitivity and specificity of the mfVEP test showed very promising results and correlated with other anatomical changes in glaucoma field loss.

The role of hemifield sector analysis in multifocal visual evoked potential objective perimetry in the early detection of glaucomatous visual field defects

Objective

The purpose of this study was to examine the effectiveness of a new analysis method of mfVEP objective perimetry in the early detection of glaucomatous visual field defects compared to the gold standard technique.

Methods and patients

Three groups were tested in this study; normal controls (38 eyes), glaucoma patients (36 eyes), and glaucoma suspect patients (38 eyes). All subjects underwent two standard 24-2 visual field tests: one with the Humphrey Field Analyzer and a single mfVEP test in one session. Analysis of the mfVEP results was carried out using the new analysis protocol: the hemifield sector analysis protocol.

Results

Analysis of the mfVEP showed that the signal to noise ratio (SNR) difference between superior and inferior hemifields was statistically significant between the three groups (analysis of variance, P < 0.001 with a 95% confidence interval, 2.82, 2.89 for normal group; 2.25, 2.29 for glaucoma suspect group; 1.67, 1.73 for glaucoma group). The difference between superior and inferior hemifield sectors and hemi-rings was statistically significant in 11/11 pair of sectors and hemi-rings in the glaucoma patients group (t-test P < 0.001), statistically significant in 5/11 pairs of sectors and hemi-rings in the glaucoma suspect group (t-test P < 0.01), and only 1/11 pair was statistically significant (t-test P < 0.9). The sensitivity and specificity of the hemifield sector analysis protocol in detecting glaucoma was 97% and 86% respectively and 89% and 79% in glaucoma suspects. These results showed that the new analysis protocol was able to confirm existing visual field defects detected by standard perimetry, was able to differentiate between the three study groups with a clear distinction between normal patients and those with suspected glaucoma, and was able to detect early visual field changes not detected by standard perimetry. In addition, the distinction between normal and glaucoma patients was especially clear and significant using this analysis.

Conclusion

The new hemifield sector analysis protocol used in mfVEP testing can be used to detect glaucomatous visual field defects in both glaucoma and glaucoma suspect patients. Using this protocol, it can provide information about focal visual field differences across the horizontal midline, which can be utilized to differentiate between glaucoma and normal subjects. The sensitivity and specificity of the mfVEP test showed very promising results and correlated with other anatomical changes in glaucomatous visual field loss. The intersector analysis protocol can detect early field changes not detected by the standard Humphrey Field Analyzer test.

Stimulus parameters for multifocal pupillographic objective perimetry

PURPOSE

We compared the diagnostic power of 10 stimulus variants that assessed the visual fields of both eyes by recording pupillary responses to multifocal stimuli. The 10 variants comprised 6 initial tests, and 4 subsequent variants whose design was informed by the initial results.

METHODS

Two study groups containing 16 normal and 22 primary open angle glaucoma subjects, and 15 normal and 20 primary open angle glaucoma subjects had their diagnostic status verified by a slit-lamp investigation, applanation tonometry, 3 forms of perimetry, and Stratus OCT. Stereoscopically arranged displays presented multifocal stimulus arrays having 24 stimulus regions/eye within the central 60 degrees. Pupil responses were recorded by video cameras under infrared illumination. The 10 stimulus conditions varied in presentation rate, duration, stimulus luminance, and flicker rate. Stimuli were 4 minutes in duration, presented in 8 segments of 30 seconds. Up to 15% of the data of a segment could be lost owing to blinks and fixation losses without repeating the segment.

RESULTS

Each recording gave 96 direct and consensual responses/subject. The best performing stimulus method gave a sensitivity of 1.0 ± 0.0 (mean ± SE) for moderate and severe glaucomatous fields combined at a false positive rate of 0.05. Median signal to noise ratios for peak response amplitude expressed as t-statistics exceeded 4 for several variants.

CONCLUSIONS

Stimulus delivery rates of about 1 presentation/region/s and test luminance around 150 cd/m performed best diagnostically. Unlike automated perimetry, the mfPOP method provides information on response delays and afferent and efferent defects at each region of the visual field.

Multifocal visual evoked potentials in unilateral compressive optic neuropathy secondary to orbital tumors

OBJECTIVE

To evaluate the effects of unilateral compressive optic neuropathy secondary to orbital tumors and the removal of the tumors on amplitude and latency of multifocal visual evoked potentials (mfVEPs) and to compare these responses with visual field defects seen on static automated perimetry.

METHODS

Static automated and mfVEP recordings were obtained from 14 patients with orbital tumors affecting one optic nerve. Monocular and interocular amplitude and latency analyses were performed.

RESULTS

The change in the mfVEP amplitude agreed with visual field findings with regard to topography and severity of deviation from normal in 10 patients. For 4 patients with normal visual field, the changes in the mfVEP were of significance. The delay in recordable responses from affected eyes ranged from 2.56 to 18.28 ms (interocular analysis) and 0.1 to 21.86 ms (monocular analysis). Ten patients whose tumor was totally removed showed a recovery of the visual field and mfVEP to various degrees. Visual field of 6 patients showed within normal limits after total removal of the tumor, and the defects of mfVEP in 3 patients remained apparent, while the mfVEP of the other 3 patients showed a complete recovery.

CONCLUSIONS

Various orbital tumors can cause compressive optic neuropathy. Compressive optic neuropathy secondary to orbital tumors results in mfVEP amplitude reduction and latency prolongation. The changes in measures of mfVEP due to orbital tumors are consistent with the visual field changes in most patients. In some patients, the subjective visual field results and objective mfVEP are discordant. The objective changes of mfVEP may appear earlier than the defect of visual field, and thus it may be able to identify subtle defects that are undetectable with Humphrey perimetry. Postoperatively, recovery of the mfVEP may be later than that of visual field in some patients. The mfVEP changes may assist in both early diagnosis and follow-up of the compressive optic neuropathy secondary to orbital tumors.

Perimetric and retinal nerve fiber layer findings in patients with Parkinson's disease

Background

Visual dysfunction is common in Parkinson’s disease (PD). It remains, however, unknown whether it is related to structural alterations of the retina. The aim of this study is to compare visual field (VF) findings and circumpapillary retinal nerve fiber layer (RNFL) thickness in a series of PD patients and normal controls, in order to assess possible retinal anatomical changes and/or functional damage associated with PD.

Methods

PD patients and controls were recruited and underwent VF testing with static automated perimetry and RNFL examination with optical coherence tomography (OCT). Cognitive performance using Mini Mental State Examination (MMSE), PD staging using modified Hoehn and Yahr (H-Y) scale and duration of the disease was recorded in PD patients.

Results

One randomly selected eye from each of 24 patients and 24 age-matched controls was included. OCT RNFL thickness analysis revealed no difference in the inferior, superior, nasal or temporal sectors between the groups. The average peripapillary RNFL was also similar in the two groups. However, perimetric indices of generalized sensitivity loss (mean deviation) and localized scotomas (pattern standard deviation) were worse in patients with PD compared to controls (p < 0.01). 73% of eyes of PD patients had glaucomatous-like asymmetrical hemifield defects with abnormal Glaucoma Hemifield Test and various combinations of arcuate defects (n = 12), nasal steps (n = 11) and paracentral scotomas (n = 16). Bilateral defects were found in 14 patients (58%). No correlation was found between VF indices and MMSE or H-Y scores.

Conclusion

PD patients may demonstrate glaucomatous-like perimetric defects even in the absence of decreased RNFL thickness.

Evaluation of multifocal visual evoked potentials in patients with Graves' orbitopathy and subclinical optic nerve involvement

Dysthyroid optic neuropathy is the most serious, although infrequent (8-10 %) complication in Graves' orbitopathy (GO). It is known that early stages of compressive optic neuropathy may produce reversible visual field defects, suggesting axoplasmic stasis rather than ganglion cell death. This observational, cross-sectional, case-control study assessed 34 consecutive patients (65 eyes) with Graves' hyperthyroidism and longstanding GO and 31 age-matched control subjects. The patients' multifocal visual evoked potentials (mfVEP) were compared to their clinical and psychophysical (standard automated perimetry [SAP]) and structural (optic coherence tomography [OCT]) diagnostic test data. Abnormal cluster defects were found in 12.3 % and 3.1 % of eyes on the interocular and monocular amplitude analysis mfVEP probability plots, respectively. As well, mfVEP latencies delays were found in 13.8 and 20 % of eyes on the interocular and monocular analysis probability plots, respectively. Interestingly, 19 % of patients with GO had ocular hypertension, and a strong correlation between intraocular pressure measured at upgaze and mfVEP latency was found. MfVEP amplitudes and visual acuity were significantly related to each other (P < 0.05), but not with the latencies delays. However, relationships between the interocular or monocular mfVEP amplitudes and latencies analysis and SAP indices or OCT data were not statistically significant. One-third of our patients with GO showed changes in the mfVEP, indicating significant subclinical optic nerve dysfunction. In this sense, the mfVEP may be a useful diagnostic tool in the clinic for early diagnosis and monitoring of optic nerve function abnormalities in patients with GO.

Clinical use of multifocal visual-evoked potentials in a glaucoma practice: a prospective study

PURPOSE

To test a framework that describes how the multifocal visual-evoked potential (mfVEP) technique is used in a particular glaucoma practice.

METHODS

In this prospective, descriptive study, glaucoma suspects, ocular hypertensives and glaucoma patients were referred for mfVEP testing by a single glaucoma specialist over a 2-year period. All patients underwent standard automated perimetry (SAP) and mfVEP testing within 3 months. Two hundred and ten patients (420 eyes) were referred for mfVEP testing for the following reasons: (1) normal SAP tests suspected of early functional loss (ocular hypertensives, n = 43; and glaucoma suspects on the basis of suspicious optic disks, n = 52); (2) normal-tension glaucoma patients with suspected central SAP defects (n = 33); and (3) SAP abnormalities needing confirmation (n = 82).

RESULTS

All the glaucoma suspects with normal SAP and mfVEP results remained untreated. Of those with abnormal mfVEP results, 68 % (15/22) were treated because the abnormal regions on the mfVEP were consistent with the abnormal regions seen during clinical examination of the optic disk. The mfVEP was abnormal in 86 % (69/80) of eyes with glaucomatous optic neuropathy and SAP damage, even though it did not result in an altered treatment regimen. In NTG patients, the mfVEP showed central defects in 44 % (12 of 27) of the eyes with apparently normal central fields and confirmed central scotomata in 92 % (36 of 39), leading to more rigorous surveillance of these patients.

CONCLUSIONS

In a clinical practice, the mfVEP was used when clinical examination and subjective visual fields provided insufficient or conflicting information. This information influenced clinical management.

Contrast-response functions of the multifocal steady-state VEP (MSV)

OBJECTIVES

To measure contrast-response functions (CRFs) for 9 visual field (VF) regions and nonlinear interactions between regions using a multifocal steady-state VEP (MSV).

METHODS

Ten normal adults were tested (51.7 ± 16.9 yr, 5 females). Stimuli resembling those of the Frequency Doubling Technology (FDT) perimeter were presented in 9 VF regions simultaneously, which were modulated at incommensurate temporal frequencies (mean 19.7 Hz). Responses were recorded to 11 contrasts from 3% to 89%, using 8 scalp electrodes. Two repeats of a 20s duration stimulus were averaged for each contrast.

RESULTS

The CRFs were log-linear except for a depression near 7% contrast (p=0.0008), which was prominent in the central VF. The effects of VF region, stimulus frequency and recording electrode were significant (all p<0.016). Significant responses at frequencies corresponding to interactions between VF regions also appeared. Electrodes that were best for the interactions and second harmonic responses differed, suggesting different cortical sources.

CONCLUSIONS

Despite short recording durations the saturating CRFs meant that significant responses could be measured to low contrasts, and be distinguished from nonlinear interactions.

SIGNIFICANCE

Recording MSVs to low contrast FDT-like stimuli might be useful for quantifying damage by glaucoma and other visual disorders.

Evaluation of the visual function in obstructive sleep apnea syndrome patients and normal-tension glaucoma by means of the multifocal visual evoked potentials

BACKGROUND

This study was designed to objectively evaluate visual function and the causal relationship between sleep apnea and optic nerve dysfunction in patients with obstructive sleep apnea syndrome (OSAS) with or without diagnosis of normal-tension glaucoma (NTG) using multifocal visual evoked potentials (mfVEP).

METHODS

This observational, cross-sectional study assessed 20 patients with recently diagnosed OSAS with or without NTG. Diagnosis of sleep apnea was based on overnight polysomnography (ApnoeScreen). All participants underwent a complete physical and ophthalmologic examination. MfVEP recordings obtained using VERIS software (Electro-Diagnostic Imaging, San Mateo, USA), SITA-standard 30-2 automated perimetry (Humphrey Visual Field Analyzer II) and optic coherence tomography (Topcon 3D OCT-1000) exams were performed to evaluate the changes.

RESULTS

Abnormal mfVEP amplitudes defects (interocular and monocular probability analysis) were found in 40% of the eyes in the non-glaucoma group and in 90% of eyes of the NTG patients. As well, delayed mfVEP latencies (interocular and monocular probability analysis) were seen in 30 and 60% of the eyes of the non-glaucoma and NTG groups, respectively. The average RNFL (retinal nerve fiber layer) thickness was significantly reduced in the NTG eyes compared to the control database and the non-glaucoma eyes. On the Humphrey Visual Field total deviation analysis, all the NTG eyes showed significant clusters of abnormal points but none was detected in the non-glaucoma group eyes. However, the mfVEP amplitude and latency did not show any significant correlation with the standard perimetry and OCT variables, because the mfVEP technique was able to detect far more early visual defects in these patients. Systolic blood pressure, sleep efficiency, arousal index, mean and minimum arterial oxygen saturation (SaO(2)), time SaO(2) < 90%, oxyhemoglobin desaturation index, number of central and mixed apneas and apnea-hipopneas index were shown to be significantly correlated with mfVEP amplitude and latency.

CONCLUSIONS

A significant incidence of subclinical optic nerve involvement, not detected with other structural and psychophysics diagnostic techniques was seen by means of the mfVEP. In this sense, the mfVEP may be a useful diagnostic tool in the clinic for early diagnosis and monitoring of optic nerve function abnormalities in patients with OSAS.

Effects of acutely lowering intraocular pressure on the results of multifocal visual evoked potential testing

PURPOSE

There have been many reports in the literature on the apparent reversal of optic nerve cupping in patients with glaucoma after lowering intraocular pressure (IOP) on clinical examination, as well as improvement in visual field testing, and increased nerve fibre layer thickness on optical coherence tomography. No studies to date have looked at improvement of multifocal visually evoked potentials (mfVEP) after lowering IOP.

METHODS

This was a prospective study of twenty consecutive patients with elevated IOP seen in the glaucoma department of Wills Eye Institute. Patients who met the inclusion criteria for this study had a complete eye examination including IOP measurement and underwent testing with mfVEP, Heidelberg Retinal Tomograph (HRT) and static achromatic automated perimetry with SITA-Standard 24-2 program Humphrey visual field (HVF) studies at baseline and 2 h post-IOP reduction. A minimum of 30% IOP reduction was required. IOP changes were then compared with various parameters of mfVEP, HRT and HVF using Spearman rank correlation coefficients.

RESULTS

The Spearman rank correlation values between change in IOP versus various parameters were calculated: Accumap severity index (ASI), 0.37 (p = 0.14); Accumap superior hemifield, 0.049 (p = 0.85); Accumap inferior hemifield, 0.030 (p = 0.91); HVF mean deviation, 0.081 (p = 0.76); HRT rim area, 0.17 (p = 0.51); HRT cup area, -0.006 (p = 0.98). Weak positive but insignificant correlations were seen for all parameters except cup area.

CONCLUSIONS

This pilot study failed to confirm statistically significant correlations between IOP reduction and changes in Accumap, HVF and HRT measures, although positive correlations were seen for most measures.

Receiver-operating characteristic analysis of multifocal VEPs to diagnose and quantify glaucomatous functional damage

To test whether multifocal visual evoked potential (mfVEP) recording using two perpendicularly placed channels, as previously reported, to measure the degree of signal-to-noise ratio (SNR) distribution overlap between a signal window and a noise window would efficiently detect and quantify glaucomatous damage. Humphrey visual field (HVF) and mfVEP were recorded from 56 patients with primary open-angle glaucoma and mean deviation less than -15 dB and 62 age-matched ophthalmologically normal individuals. Areas under the receiver-operating characteristic curve (SNR-AUC) were calculated based on the proportion of mfVEP responses that exceeded a specific SNR criterion for both windows. Abnormal sectors with an SNR deviated from the previously established norm with P<5% and 1% were counted. Diagnostic accuracy of the SNR-AUC was similar to that of the average total deviation (TD) of the HVF. The hemifield agreement to detect a defect in mfVEP and HVF was 77.1-87.3%, which was similar to previous reports using multiple channels. Correlation coefficients between SNR-AUC and average TD (0.74 in the upper hemifield and 0.65 in the lower) were significantly higher than those between the sums of abnormal locations on the mfVEP and HVF probability plots (0.27 and 0.33, respectively). Two perpendicular channels can detect and quantify functional damage due to glaucoma. The SNR-AUC may be used as a global index to quantify diffuse glaucomatous functional loss.

Beta-zone parapapillary atrophy and multifocal visual evoked potentials in eyes with glaucomatous optic neuropathy

We investigated changes in multifocal visual evoked potential (mfVEP) responses due to beta-zone parapapillary atrophy (ßPPA). Patients with glaucomatous optic neuropathy (GON) with or without standard achromatic perimetry (SAP) abnormalities were referred for mfVEP testing during a 2-year period. Eyes with good quality optic disc stereophotographs and reliable SAP results were included. The mfVEP monocular mean latency delays (ms) and amplitudes (SNR) were analyzed. Age, SAP mean deviation (MD), pattern standard deviation (PSD), and spherical equivalent (SE) were analyzed in the multivariate model. Generalized estimated equations were used for comparisons between groups after adjusting for inter-eye associations. Of 394 eyes of 200 patients, 223 (57%) had ßPPA. The ßPPA eyes were older (59.6 ± 13.7 vs. 56.5 ± 13.7 year, P = 0.02), more myopic (-4.0 ± 3.5 vs. -1.3 ± 3.5 D, P < 0.01), and had poorer SAP scores (MD: -4.9 ± 5.2 vs. -2.6 ± 5.2 dB, P < 0.01; PSD: 4.3 ± 2.9 vs. 2.5 ± 3.0 dB, P < 0.01). By univariate analysis, mean latencies were longer in ßPPA eyes (6.1 ± 5.3 vs. 4.0 ± 5.5 ms, P < 0.01). After adjusting for differences in SE, age, and SAP MD, there was no significant difference between the two groups (P = 0.09). ßPPA eyes had lower amplitude log SNR (0.49 ± 0.16 vs. 0.56 ± 0.15, P < 0.01), which lost significance (P = 0.51) after adjusting for MD and PSD. Although eyes with ßPPA had significantly lower amplitudes and prolonged latencies than eyes without ßPPA, these differences were attributable to differences in SAP severity, age, and refractive error. Thus, ßPPA does not appear to be an independent factor affecting mfVEP responses in eyes with GON.

Application of multifocal visual evoked potentials in the assessment of visual dysfunction in macular diseases

PURPOSE

To evaluate the use of AccuMap multifocal visual evoked potentials (mfVEP) in visual dysfunction caused by macular diseases.

METHODS

Forty-eight eyes with known macular diseases underwent AccuMap mfVEP and microperimetry 1 (MP1) assessments. Evaluation of mfVEP abnormality was based on an amplitude deviation probability plot and the AccuMap Severity Index (ASI). Correlation analyses of the mean mfVEP amplitude corresponding to a radius of 2°, 5°, and 10° of the central visual field, minimum angle of resolution best-corrected visual acuity (BCVA), and MP1 mean sensitivity of the corresponding areas were performed.

RESULTS

Among the 48 affected eyes, AccuMap mfVEP detected an abnormality of the central visual field in 45 eyes, with a sensitivity of 93.8%. The mean mfVEP amplitudes within a radius of 2°, 5°, and 10° of the central visual field were found to be positively correlated with BCVA (P<0.01 for all groups). The mean amplitudes also positively correlated with the MP1 mean sensitivity value of the corresponding visual field (P<0.01 for all groups). In the group with stable fixation or predominantly central fixation, the mean mfVEP amplitudes did not correlate with the BCVA or the MP1 mean sensitivity value. Regardless of the fixation status, the ASI was found to correlate with both the BCVA and the total MP1 mean defect value.

CONCLUSION

Objective perimetry using AccuMap mfVEP might be applied in the assessment of macular function, with the ASI offering a potentially useful indicator for evaluating macular dysfunction.

Initial arcuate defects within the central 10 degrees in glaucoma

PURPOSE

To better understand the relationship between the spatial patterns of functional (visual field [VF] loss) and structural (axon loss) abnormalities in patients with glaucomatous arcuate defects largely confined to the central 10° on achromatic perimetry.

METHODS

Eleven eyes (9 patients) with arcuate glaucomatous VF defects largely confined to the macula were selected from a larger group of patients with both 10-2 and 24-2 VF tests. Eyes were included if their 10-2 VF had an arcuate defect and if the 24-2 test was normal outside the central 10° (i.e., did not have a cluster of three contiguous points within a hemifield). For the structural analysis, plots of retinal nerve fiber layer (RNFL) thickness of the macula were obtained with frequency-domain optical coherence tomography (fdOCT). The optic disc locations of the RNFL defects were identified on peripapillary fdOCT scans.

RESULTS

The VF arcuate defects extended to within 1° of fixation on the 10-2 test and were present in the superior hemifield in 10 of the 11 eyes. The arcuate RNFL damage, seen in the macular fdOCT scans of all 11 eyes, involved the temporal and inferior temporal portions of the disc on the peripapillary scans.

CONCLUSIONS

Glaucomatous arcuate defects of the macula's RNFL meet the disc temporal to the peak of the main arcuate bundles and produce a range of macular VF defects from clear arcuate scotomas to a papillofoveal horizontal step ("pistol barrel scotoma"). If RGC displacement is taken into consideration, the RNFL and VF defects can be compared directly.

Simultaneous recording of multifocal VEP responses to short-wavelength and achromatic stimuli

A paradigm is introduced that allows for simultaneous recording of the pattern-onset multifocal visual evoked potentials (mfVEP) to both short-wavelength (SW) and achromatic (A) stimuli. There were 5 sets of stimulus conditions, each of which is defined by two semi-concurrently presented stimuli, A64/SW (a 64% contrast achromatic stimulus and a short-wavelength stimulus), A64/A8 (64% achromatic/8% achromatic), A0/A8 (0% (gray) achromatic/8% achromatic), A64/A0 and A0/SW. When paired with A64 as part of A64/SW, the SW stimulus yielded mfVEP responses (SWmfVEP) with diminished amplitude in the fovea, consistent with the known sensitivity of the S-cone system. In addition, when A8, which is approximately equal to the L and M cone contribution of the SW stimulus, was recorded alone, the response to A8 was small, but significantly larger than noise. However, when A8 was paired with A64, the response to A8 was reduced to close to noise level, suggesting that the LM cone contribution of the SWmfVEP can be suppressed by A64. When A64 was recorded alone, the response to A64 was about 32% larger than the mfVEP for A64 when paired with the SW. Likewise, the presence of A64 stimulus also reduces the response of SWmfVEP by 35%. Finally, an intense narrow-band yellow background prolonged the latency of SW response for the A0/SW stimulus but not the latency of SW response for the A64/SW stimulus. These results indicate that it is possible to simultaneously record an SWmfVEP with little LM cone contribution along with an achromatic mfVEP.

Comparison of multifocal visual evoked potential, standard automated perimetry and optical coherence tomography in assessing visual pathway in multiple sclerosis patients

BACKGROUND

Multifocal visual evoked potentials (mfVEP) measure local response amplitude and latency in the field of vision.

OBJECTIVE

To compare the sensitivity of mfVEP, Humphrey visual field (HVF) and optical coherence tomography (OCT) in detecting visual abnormality in multiple sclerosis (MS) patients.

METHODS

mfVEP, HVF, and OCT (retinal nerve fiber layer [RNFL]) were performed in 47 MS-ON eyes (last optic neuritis [ON] attack >or=6 months prior) and 65 MS-no-ON eyes without ON history. Criteria to define an eye as abnormal were: (1) mfVEP amplitude/latency - either amplitude or latency probability plots meeting cluster criteria with 95% specificity; (2) mfVEP amplitude or latency alone (specificity: 97% and 98%, respectively); and (3) HVF and OCT, mean deviation and RNFL thickness meeting p < 0.05, respectively.

RESULTS

MfVEP (amplitude/latency) identified more abnormality in MS-ON eyes (89%) than HVF (72%), OCT (62%), mfVEP amplitude (66%) or latency (67%) alone. Eighteen percent of MS-no-ON eyes were abnormal for both mfVEP (amplitude/latency) and HVF compared with 8% with OCT. Agreement between tests ranged from 60% to 79%. mfVEP (amplitude/latency) categorized an additional 15% of MS-ON eyes as abnormal compared with HVF and OCT combined.

CONCLUSIONS

mfVEP, which detects both demyelination (increased latency) and neural degeneration (reduced amplitude), revealed more abnormality than HVF or OCT in MS patients.

Assessing visual pathway function in multiple sclerosis patients with multifocal visual evoked potentials

Multifocal visual evoked potentials provide a topographic measure of visual response amplitude and latency. The objective of this study was to evaluate the sensitivity and specificity of the multifocal visual evoked potential technique in detecting visual abnormalities in patients with multiple sclerosis. Multifocal visual evoked potentials were recorded from 74 patients with multiple sclerosis with history of optic neuritis (MS-ON, n = 74 eyes) or without (MS-no-ON, n = 71 eyes), and 50 normal subjects (controls, n = 100 eyes) using a 60-sector pattern reversal dartboard stimulus (VERIS). Amplitude and latency for each sector were compared with normative data and assigned probabilities. Size and location of clusters of adjacent abnormal sectors (p < 0.05) were examined. Mean response amplitudes were (+/- SE) 0.39 +/- 0.02, 0.53 +/- 0.02, and 0.60 +/- 0.01 for MS-ON, MS-no-ON, and control groups, respectively, with significant differences between all groups (p < 0.0001). Mean latencies (ms; +/-SE relative to normative data) were 12.7 +/- 1.3 (MS-ON), 4.3 +/- 1.1 (MS-no-ON), and 0.3 +/- 0.4 (controls); group differences again significant (p < 0.0001). Half the MS-ON eyes had clusters larger than five sectors compared with 13% in MS-no-ON and 2% in controls. Abnormal sectors were distributed diffusely, although the largest cluster was smaller than 15 sectors in two-thirds of MS-ON eyes. Cluster criteria combining amplitude and latency showed an area of 0.96 under the receiver operating characteristic curve, yielding a criterion with 91% sensitivity and 95% specificity. We conclude that the multifocal visual evoked potential provides high sensitivity and specificity in detecting abnormalities in visual function in multiple sclerosis patients.

Multifocal pupillographic visual field testing in glaucoma

PURPOSE

This preliminary study investigated a means of concurrently assessing the visual field defects of both eyes by recording pupillary responses to multifocal stimuli.

METHODS

Twenty normal subjects and 26 primary open angle glaucoma patients, age and sex matched, were examined by slit-lamp, Humphrey Field Analyser II achromatic 24-2 perimetry and fundus photography. The patients had moderate to severe fields in at least one eye. Two stereoscopically arranged displays presented an array of 24 stimulus regions per eye extending from fixation to 30 degrees eccentricity. Pupil responses were recorded by video cameras under infrared illumination. Four stimulus conditions were tested: each stimulus region containing either a single or a 2 x 2 array of patches, presented either steadily for 133 ms or flickered at 15 Hz for 266 ms. Mean presentation rate was 1/s/region. The 4-min duration stimuli were presented in 8 segments of 30 s. Segments did not need to be repeated unless more than 15% of a segment record was lost as a result of blinks or fixation losses.

RESULTS

The 48 stimuli produced 96 direct and consensual responses per subject. The single patch, non-flickered stimulus condition produced the best diagnostic performance, an area under the curve of 84%. The contraction amplitudes for that stimulus gave a median z-score of 3.2.

CONCLUSIONS

The method produced diagnostic accuracy approaching that of automated perimetry, but unlike perimetry provides standard errors for every point in each field as well as information on response delay and efferent defects. Only one pupil needs to function to measure both visual fields.

Multifocal frequency-doubling pattern visual evoked responses to dichoptic stimulation

OBJECTIVE

To examine the feasibility of a multifocal visual evoked potential (mfVEP) binocularly, using a variant of the multifocal frequency-doubling (FD) pattern-electroretinogram (MFP).

METHODS

Stimuli were presented in both monocular and dichoptic conditions at eight visual field locations/eye. The incommensurate stimulus frequencies ranged from 15.45 to 21.51 Hz. Five stimulus conditions differing in spatial frequency and orientation were examined for three viewing conditions. The resulting 15 stimulus conditions were examined in 16 normal subjects who repeated all conditions twice.

RESULTS

Several significant independent effects were identified. Response amplitudes were reduced for dichoptic viewing (by 0.85 times, p<4 x 10(-11)); offset by increases in responses for between eye differences of one octave of spatial frequency: lower (1.15 times, 0.1 cpd); higher (1.29 times, 0.4 cpd), both p<1.8 x 10(-7). Crossed orientations produced significant effects upon response phase (p=0.023) but not amplitude (p=0.062).

CONCLUSIONS

The results indicated that dichoptic evoked potentials using multifocal frequency-doubling illusion stimuli are practical. The use of crossed orientation, or differing spatial frequencies, in the two eyes reduced binocular interactions.

SIGNIFICANCE

The results indicate a method wherein several spatial or temporal and frequencies per visual field region can be tested in reasonable time using a multifocal VEP using spatial frequency-doubling stimuli.

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.

Multifocal visual evoked potential responses to pattern-reversal, pattern-onset, pattern-offset, and sparse pulse stimuli

The purpose of the present study was to compare standard multifocal visual evoked potential (mfVEP) pattern-reversal responses with those produced by pattern-onset, pattern-offset, and pulsed pattern stimuli. mfVEP recordings were obtained from five normal subjects using VERIS and a 4-electrode array. The standard reversal stimulus had 2(15) m-sequence steps (7.5-min duration). Pattern-onset and -offset responses were evaluated using sequences that all had 32 frames per m-step and 2(10) total steps (7.5 min); but the duration of the contrast step varied so that it was 1, 2, 4, 8, 12, or 16 of the 32 frames. The same series was also inverted so that adapting contrast was high and the stimulus step began with a contrast decrement. The effect of temporal sparseness was studied with positive contrast pulses (two-frame duration) within 16, 20, 24, 28, or 32 frames per m-step (all had 2(11) total steps). Four stimulus locations were isolated to study the effect of spatial sparseness. Standard mfVEP reversal responses were virtually identical to onset responses throughout the field, but ~3.5 times smaller. Responses to pattern onset were about twice as large as those for offset, especially in the lower hemifield, irrespective of adapting contrast level. Offset responses exhibited a different waveform compared with reversal, onset, or brief pulse responses. Though temporally sparse pattern-pulse responses were ~3.5 times larger than standard reversal responses, there was no improvement in signal-to-noise ratio (SNR). However, spatial isolation increased SNR by 22% for reversal responses and by 62% for temporally sparse pulses. Temporally sparse pattern-pulse stimuli do not improve mfVEP SNR unless they are also spatially sparse, suggesting that lateral inhibitory mechanisms have a greater impact than temporal contrast gain control mechanisms. The mfVEP response depends on the polarity of a contrast step, irrespective of the state of contrast adaptation.

Repeatability of the multifocal visual evoked potentials in a clinical glaucoma setting

BACKGROUND

To determine the reproducibility of the multifocal visual evoked potentials (mfVEP) test results in a clinical glaucoma setting, and the factors that affect variability.

METHODS

This was an observational case series study. The monocular mfVEP test, having a 58-sector, pattern-reversal dartboard array, was performed twice within 4 weeks in both eyes of 29 adult open-angle glaucoma (OAG) patients and suspects, using AccuMap Opera Software (ObjectiVision Pty Ltd, Sydney, Australia). The AccuMap severity index (ASI), the mean amplitude, and the individual amplitudes in each sector were compared between the 2 tests using intraclass correlations (ICCs). The effects of the severity of mfVEP field defects and signal-to-noise ratio (SNR) on the reproducibility of these variables were determined using the McNemar test and the Spearman rank correlation, respectively.

RESULTS

The average ICCs of the ASI and amplitudes in the 2 tests were 0.84 and 0.87, respectively. Two sectors in the right eye and 6 in the left eye had significant differences between the 2 tests (Wilcoxon signed-rank p < 0.05). Larger differences were observed in patients having lower SNR (Spearman p = 0.022). Forty-six of the 58 eyes stayed within the same diagnosis category on repeating the test (i.e., within normal limits or outside normal limits).

INTERPRETATION

Although there were some isolated examples of clinically significant differences on repeating the mfVEP test in our patients, our results suggest overall good repeat reliability. The variability of the test was higher in patients having high noise levels during the test.

A method to detect progression of glaucoma using the multifocal visual evoked potential technique

PURPOSE

To describe a method for monitoring progression of glaucoma using the multifocal visual evoked potential (mfVEP) technique.

METHODS

Eighty-seven patients diagnosed with open-angle glaucoma were divided into two groups. Group I, comprised 43 patients who had a repeat mfVEP test within 50 days (mean 0.9 +/- 0.5 months), and group II, 44 patients who had a repeat test after at least 6 months (mean 20.7 +/- 9.7 months). Monocular mfVEPs were obtained using a 60-sector pattern reversal dartboard display. Monocular and interocular analyses were performed. Data from the two visits were compared. The total number of abnormal test points with P < 5% within the visual field (total scores) and number of abnormal test points within a cluster (cluster size) were calculated. Data for group I provided a measure of test-retest variability independent of disease progression. Data for group II provided a possible measure of progression.

RESULTS

The difference in the total scores for group II between visit 1 and visit 2 for the interocular and monocular comparison was significant (P < 0.05) as was the difference in cluster size for the interocular comparison (P < 0.05). Group I did not show a significant change in either total score or cluster size.

CONCLUSION

The change in the total score and cluster size over time provides a possible method for assessing progression of glaucoma with the mfVEP technique.

Multifocal VEP and OCT in optic neuritis: a topographical study of the structure-function relationship

PURPOSE

To investigate topographical relationship between amplitude of multifocal visual evoked potentials (mfVEP) and retinal nerve fibre layer (RNFL) thickness following acute optic neuritis (ON).

PATIENTS AND METHODS

Fifty patients with a clinical diagnosis of acute unilateral ON between 6 and 36 months prior to the study and 25 age-matched controls underwent mfVEP testing (Accumap V 2.1, ObjectiVision Pty Ltd, Sydney, Australia) and OCT imaging (fast RNFL protocol, Stratus, software version 3.0, Carl Zeiss Meditec, Inc., Dublin, CA). RNFL thickness and mfVEP amplitude were measured for upper, temporal and lower retinal sectors and corresponding areas of the visual field in affected eyes of ON patients and control eyes. Inter-eye asymmetry coefficients for both RNFL thickness and mfVEP amplitude were calculated for each zone, and corresponding coefficients were correlated between each other.

RESULTS

There was highly significant reduction of RNFL thickness and mean mfVEP amplitude in all three retinal sectors of the affected eye. Largest reduction of RNFL thickness was noticed in temporal sector and of mfVEP amplitude in corresponding central part of the visual field. RNFL thickness correlated highly with amplitude of the mfVEP derived from corresponding areas of the visual field in all three zones.

CONCLUSIONS

We demonstrated strong topographical associations between structural and functional measures of optic nerve integrity in patients with ON.

Glaucoma affects steady state VEP contrast thresholds before psychophysics

PURPOSE

Frequency doubling technology (FDT) is a recent psychophysical test for glaucoma. It measures the contrast threshold to low spatial frequency, high temporal frequency sinusoidal luminance profile bars. We wanted to confirm, with stricter controls, Vaegan and Hollow's report that contrast thresholds of steady state visual evoked potentials (ssVEPs) to a stimulus resembling the central field of the FDT test was more sensitive to glaucoma than the subjective threshold to the same stimulus and to start to optimize the technique.

METHODS

A double masked trial using 57 eyes of 42 subjects. Both thresholds were estimated by modified binary search. In psychophysical testing, subjects were given a two alternative forced choice task. In ssVEP testing a significant signal in any one of eight channels was deemed to be a detection. In some subjects electrode positions were compared, both eyes were tested, tests were repeated to estimate reliability, stimulus frequencies were varied or full contrast functions were obtained.

RESULTS

Thresholds and percent abnormal increased as a function of glaucoma severity for ssVEPs but not for psychophysics. Both threshold measures were reliable. Interocular correlations were low. SsVEP amplitude against contrast functions had similar thresholds to those found by modified binary search. The data was too irregular for individual thresholds to be estimated from a fitted exponential. Amplitudes were greatest at 7 to 10 Hz, < or =6 cm above inion and least laterally. Noise was similar across electrodes.

CONCLUSIONS

SsVEP contrast thresholds to a stimulus like the central field of the FDT test detected glaucoma better than corresponding psychophysical thresholds at 18.29 Hz, when formal controls were used, as they had in a less controlled previous study at 7.14 Hz.

Update on the pattern electroretinogram in glaucoma

PURPOSE

To review the efficacy of the pattern electroretinogram (PERG) in early diagnosis of glaucoma.

METHODS

Stimulation parameters of check size and temporal frequency are considered. Analyses of various peaks (P50, N95, the N95/P50) and Fourier steady-state are considered. The relation to visual field defects is explored.

RESULTS

The PERG is markedly alterated in glaucoma. It shows amplitude reductions in (still) normal areas of the visual field. Optical imaging on the retina needs to be optimal. Higher temporal frequency (>10 reversals/s) improves the sensitivity to detect glaucoma compared with transient stimulation. The ratio between the amplitudes to 0.8 degrees checks and to 16 degrees checks, "PERG ratio," exploits a check size-specific reduction in early glaucoma and reduces variability. Longitudinal studies suggest that the PERG can indicate incipient glaucoma damage before evidence from the visual field.

CONCLUSIONS

The PERG is a demanding electrophysiological technique that can serve as a sensitive biomarker for retinal ganglion cell function. With appropriate paradigms, PERG assists in identifying those patients with elevated interocular pressure in whom glaucoma damage is incipient before visual field changes occur.

Effect of recording duration on the diagnostic performance of multifocal visual-evoked potentials in high-risk ocular hypertension and early glaucoma

PURPOSE

To evaluate the effect on diagnostic performance of reducing multifocal visual-evoked potential (mfVEP) recording duration from 16 to 8 minutes per eye.

METHODS

Both eyes of 185 individuals with high-risk ocular hypertension or early glaucoma were studied. Two 8-minute mfVEP recordings were obtained for each eye in an ABBA order using VERIS. The first recording for each eye was compared against single run (1-Run) mfVEP normative data; the average of both recordings for each eye was compared against 2-Run normative data. Visual fields (VFs) were obtained by standard automated perimetry (SAP) within 22.3+/-27.0 days of the mfVEP. Stereo disc photographs and Heidelberg Retina Tomograph images were obtained together, within 24.8+/-50.4 days of the mfVEP and 33.1+/-62.9 days of SAP. Masked experts graded disc photographs as either glaucomatous optic neuropathy or normal. The overall Moorfields Regression Analysis result from the Heidelberg Retina Tomograph was used as a separate diagnostic classification. Thus, 4 diagnostic standards were applied in total, 2 based on optic disc structure alone and 2 others based on disc structure and SAP.

RESULTS

Agreement between the 1-Run and 2-Run mfVEP was 90%. Diagnostic performance of the 1-Run mfVEP was similar to that of the 2-Run mfVEP for all 4 diagnostic standards. Sensitivity was slightly higher for the 2-Run mfVEP, whereas specificity was slightly higher for the 1-Run mfVEP.

CONCLUSIONS

If higher sensitivity is sought, the 2-Run mfVEP will provide better discrimination between groups of eyes with relatively high signal-to-noise ratio (eg, early glaucoma or high-risk suspects). But if higher specificity is a more important goal, the 1-Run mfVEP provides adequate sensitivity and requires only half the test time. Considered alongside prior studies, the present results suggest that the 1-Run mfVEP is an efficient way to confirm (or refute) the extent of VF loss in patients with moderate or advanced glaucoma, particularly in those with unreliable VFs, including malingering or other "functional" forms of VF loss.

The relationship between visual field and retinal nerve fiber layer measurements in patients with multiple sclerosis

PURPOSE

To investigate the relationship between visual function, measured by standard automated perimetry (SAP), and retinal nerve fiber layer (RNFL) thickness, measured by optical coherence tomography (OCT), in patients with multiple sclerosis (MS).

METHODS

SAP and RNFL thickness were measured in patients with MS in 28 eyes with the last optic neuritis (ON) >or=6 months prior (ON group) and 33 eyes without ON history (non-ON group). Abnormal overall or quadrant RNFL thickness was defined by measured values below 5% of the norm. A whole visual field or a sector of the field was classified as abnormal by using cluster criteria on total-deviation plots. Agreement between SAP and OCT results in classifying eyes/sectors was presented as a percentage of observed agreement, along with the AC1 statistic, which corrects for chance agreement. Regression analyses were performed relating several SAP parameters and RNFL thickness in the ON group.

RESULTS

ON eyes showed more loss of visual sensitivity (MD, P = 0.02) and more loss of RNFL thickness (P < 0.0001) than did non-ON eyes. SAP and OCT agreed in 86% (AC1 = 0.78) of eyes and 69% (AC1 = 0.38) of sectors in the ON group and 61% (AC1 = 0.33) of eyes and 66% (AC1 = 0.48) of sectors in the non-ON group. Overall RNFL thickness was related to MD (dB) by a simple exponential function (R(2) = 0.48), supporting a linear relationship between these measures when both are expressed on linear scales. Absolute Pearson correlation coefficients for overall RNFL thickness and several SAP parameters ranged from 0.51 to 0.69.

CONCLUSIONS

Good agreement between SAP and OCT was found in ON eyes but not in non-ON eyes or in individual sectors in either group. The findings in this study provide further support for the utility of combining structural and functional testing in clinical research on patients with MS, as well as in future neuroprotection trials for which the anterior visual pathways in patients with MS and optic neuritis may be used as a model.