Effects of chlorpromazine on pattern and flash ERGs and VEPs compared to oxazepam and to placebo in normal subjects

Antidopaminergic drugs delay the pattern-reversal VEP (P-VEP) and the flash VEP (F-VEP) and, in separate studies, reductions in the amplitude and increases in the latencies of scotopic ERGs have been reported. This study investigated the effects of chlorpromazine (CPZ) on the pattern ERG (P-ERG), P-VEP, flash ERGs and VEPs and oscillatory potentials (OPs). Normal volunteers (N = 15) were administered a placebo, or a single dose of CPZ 100 mg or oxazepam (OZP) 15 mg at weekly intervals, in a double-blind crossover design. A gold foil-ipsilateral ear derivation and an Oz′-Fz derivation were used for the ERG and VEP recordings, respectively. The latencies of ‘mixed’ and cone ERGs were significantly prolonged after CPZ compared to both placebo and to OZP. Amplitudes of rod- and cone-dominated ERGs were reduced following CPZ administration. All components of the OPs were significantly delayed after CPZ administration. No significant intertreatment differences were found in the F-VEP results. The P-ERG P50 peak and the P-VEP N70 and P100 peaks were significantly delayed after CPZ in the case of 28′ checks but not 55′ checks. Retinocortical times and P-ERG and P-VEP amplitudes were not significantly affected. In contrast to CPZ, the administration of OZP had virtually no significant effects compared to placebo. These findings suggest that the antidopaminergic CPZ has a primary effect on retinal electrophysiology. Similar findings have been reported in Parkinson's disease and in animal models.     

Effect of spatial frequency on simultaneous recorded steady-state pattern electroretinograms and visual evoked potentials

Pattern electroretinograms (P-ERGs) and visual evoked potentials (VEPs) to 4 Hz alternating square-wave gratings were simultaneously recorded in 23 subjects. Responses were Fourier analyzed and amplitude and phase of the 2nd and 4th temporal harmonics were measured.The spatial frequency-amplitude function of the P-ERG 2nd harmonic component displayed either a bandpass tuning behavior, or a low-pass behavior. The peak amplitude for subjects with bandpass tuning was at 1.5 c/deg. The phase of the P-ERG 2nd harmonic decreased monotonically as spatial frequency increased. The VEP 2nd harmonic had a bimodal spatial frequency function with a peak at 3 c/deg and a second increase at spatial frequencies below 1 c/deg, regardless of the P-ERG characteristics. The phase of VEP 2nd and 4th harmonic had an inverted U-shaped function with peak at 3 c/deg and 1.5 c/deg respectively.Comparison of simultaneously recorded P-ERG and VEP spatial frequency functions demonstrated different tuning behavior for cortical and retinal responses. It is concluded that the proposed technique permits the separate analysis of retinal and cortical processing of visual information. The 2nd and 4th harmonic components of VEP behave independently of each other suggesting they may be generated by different subsystems.     

Multichannel visual evoked potentials in migraine

Multichannel recordings of visual evoked potentials (VEPs) have proved to be useful in the evaluation of visual field defects. We studied the topographic distribution of transient VEPs in 15 migraine patients (8 with visual aura and 7 without) and 15 age-matched controls during the migraine-free interval. All the subjects included in the study had normal visual fields. VEPs were recorded from 9 electrodes placed on the posterior scalp. Stimuli were full-field and hemifield reversing square wave grating patterns of medium spatial frequency (4 c/deg). The groups did not show significant differences in latencies and amplitudes of the major components (N70, P100) recorded from the midline. However, migraine patients with visual hemianopic aura showed definite asymmetries in the VEP amplitude distribution. Significantly reduced, absent or polarity-invered VEP responses were recorded ipsilateral to the side of the prodromic visual symptoms. Direct comparison of affected and unaffected hemispheres by partial field stimulation confirmed these findings. According to the VEP cortical generator theory, these abnormalities suggest a functional anomaly consistent with the clinical syndrome and detectable also in the migraine-free interval. None of the migraine patients without aura or the controls showed VEP amplitude asymmetries. We conclude that multichannel VEP recordings may discriminate between different subtypes of migraine and contribute important physiopathological information to the study of this disease.     

Utility of visual evoked potentials using hemifield stimulation and several check sizes in the evaluation of suspected multiple sclerosis

One hundred and eleven patients with suspected multiple sclerosis (64 possible, 47 probable) and 16 with a definite diagnosis of MS were evaluated with pattern-reversal visual evoked potentials (VEPs), employing monocular full-field checks subtending 7′, 14′ and 28′ of visual angle, and right and left hemifield 28′ checks. Thirty-seven patients (29%) had a completely normal study. Sixty-six patients (52%) had abnormal responses to full-field 28′ checks, and in 13 (10%) of these, additional abnormalities were found in one or more of the other test conditions, which indicated the presence of an additional site of dysfunction in the visual pathway. Twenty-four patients (19%) with ‘normal’ full-field 28′ response had abnormalities in one or more of the other test conditions; these included prolonged latency to small size (7′ and 14′) full-field checks, abnormal responses in homonymous hemifields, and abnormal responses limited to a hemifield of one eye. Thus, the use of several check sizes and hemifield stimulation not only increases the sensitivity of VEPs in the evaluation of patients with suspected demyelinating disease, but enhances the capability of the VEP to demonstrate more than one area of visual system impairment.     

Mapped distribution of pattern reversal VEPs to central field and lateral half-field stimuli of different spatial frequencies

Visual evoked potentials (VEPs) to pattern reversal vertical bar stimuli of 3 different sizes (1, 2, 4 c/deg) were recorded from 19 scalp derivations in 50 controls. The stimuli were presented on a full-field (FF) screen of 24° visual angle, and on left and right half-fields (HF) of 12° radius. In 15 controls partial HF stimuli were presented on the central 3 and 6° and as hemiannular stimuli of 12° with occlusion of the central 3 and 6°.An antero-posterior polarity reversal of the N1-P1-N2 sequence was observed for FF VEPs. A tangential polarity reversal was observed for HF VEPs. Also with central or hemiannular stimuli polarity reversals of all VEP components were observed within the scalp.Variants of VEP distribution, absence of prominence of some of the ipsi- or contralateral VEP components were observed in 8–40% of controls.The FF and HF VEP distribution, and the variant VEP asymmetries were partly dependent on the pattern spatial frequency.     

Scalp-recorded oscillatory potentials evoked by transient pattern-reversal visual stimulation in man

Replicable oscillatory potentials, time-locked to pattern stimuli (9.0° central; counterphase reversal at 2.13 Hz) were dissociated from conventional, broad-band VEPs recorded in healthy volunteers at occipital scalp locations by high-pass digital filtering at 17.0–20.0 Hz. Nine consecutive wavelets were identified with a 56.4 ± 8.4 msec mean latency of the first replicable wavelet and mean peak-to-peak amplitude varying between 0.9 and 2.0 μV. The first 2 wavelets had significantly shorter latencies than wave N70 of unfiltered VEP, whereas the last 2 wavelets had longer latencies than N145. Latency and amplitude values varied as a function of contrast and spatial frequency of the stimulus, with shorter latencies and larger amplitudes at 60–90% contrast level and tuning of amplitude at 5.0 c/deg. All wavelets were correlated with wave P100 of unfiltered VEP, while a correlation with N70 of VEP was observed only for those wavelets with latencies in the range of wave P100. Two patients with documented brain lesions involving the visual system are described as examples of oscillatory responses occurring irrespective of filter bandpass and instead of the expected conventional VEP when the generation of these is interfered with by brain pathology. A substantial cortical contribution to the origin of the oscillatory response is conceivable. It is suggested that the oscillatory response to pattern-reversal stimulation reflects events in the visual system that are parallel to, and partly independent of, the conventional VEP, with potential application in research or for clinical purposes.     

Three-dimensional human pattern visual evoked potentials. II. Multiple sclerosis patients

Pattern visual evoked potentials were obtained from 46 patients with definite relapsing/remitting multiple sclerosis, using both a conventional 5-channel occipital array and a 3-D recording technique consisting of three bipolar derivations approximating the three dimensions of space. These three orthogonal wave forms were displayed as a 3-D Lissajous trajectory for each subject. Two of the 15 patients with completely normal conventional pattern VEPs had abnormalities of the orientation of the B-C curvilinear segment of the 3-D pattern VEPs. Delays in the first major occipital positive component (P100) were evident using both techniques; the correlation between P100 latency and the latency of the corresponding trajectory apex was r = 0.99 (P < 0.01). Post-chiasmal MRI abnormalities were associated with 3-D VEP orientation abnormalities. Three-dimensional pattern VEPs are moderately more sensitive than conventional pattern VEPs at detecting dysfunction posterior to the optic chiasm in demyelinating disease and do not require the use of eccentric fixation to do so.     

Clinical evaluation of VEPs to interleaved checkerboard reversal stimulation of central,hemi- and peripheral fields

The VEPs of 195 patients referred for supportive evidence of multiple sclerosis or optic neuritis were studied by a new method of interleaved checkerboard reversal stimulation of different areas of the visual field. In the first group of 95 patients checks of 40′ subtense reversed in the whole field (28° × 20°), alternately in the left and right hemifields and alternately in the central (5° radius) and peripheral fields. In the second group of 100 patients checks reversed in the whole field and in interleaved mode in 3 visual field areas, comprising the central (4° radius) and left and right hemisurround fields.In the first group abnormal responses were recorded from 52 eyes and there was partial disagreement among the stimulus conditions in 10 of the 52. Abnormalities were seen uniquely to central field stimulation in 3 eyes but never to whole field stimulation alone. In the second group abnormal responses were recorded in 58 eyes, again never uniquely to whole field stimulation, while abnormalities confined to one or two areas of the visual field were seen in 24, providing evidence of peripheral field involvement alone in 8 eyes.In the first group, waveforms created from the sum of the left and right hemifield and central and peripheral field responses showed quite close conformity to the whole field VEP, although amplitudes were significantly lower and latencies significantly shorter. In 7 eyes responses would have been differently classified (normal or abnormal) using the sum as compared with the whole fields. The sum of the 3 interleaved stimuli was less reliable, its morphology often not closely approximating whole field responses.It is suggested that interleaved stimulation of two or more areas of the visual field is a sensitive and reliable method which reduces the time necessary to perform the test and helps control the patients' concentration, fixation and alertness. Whole field stimulation is probably necessary only in patients with severely degraded responses.     

The phases of visual cortex and hippocampal evoked potentials in rabbit reflect the orienting reaction in case of visual stimuli intensity changes

The oddball paradigm was applied in experiments with waking rabbits using rare (deviant) and frequent (standard) stimuli, which were similar in color but different in intensity, deviant ones being of lower intensity. In addition, the VEPs to the single deviants were averaged. Such single deviants (without standard stimuli) were given at the beginning and at the end of the stimulation. The positivity of cortical and hippocampal visual evoked potentials to deviant stimuli increased in comparison to responses to standards and single deviants. The VEP-peaks P1 and P2 in the visual cortex and the VEP P1, N1 and P2 peaks in hippocampus increased. The most prominent significant changes were demonstrated for cortical VEP P2 (P130) peak. It is suggested that the increase of positivity to oddball deviants is due to the orienting reflex arising in response to rare stimuli. The increase of P2-peak can be connected with the transfer of information signaling changes of light intensity. It was demonstrated that the most clear and contrast differences in the VEPs to deviants and standards took place for the case of minimal distinction in their intensities. This fact may reflect the orienting reactionto threshold stimuli.     

Loss of cortical function in mice after decapitation, cervical dislocation, potassium chloride injection, and CO2 inhalation

Electroencephalograms (EEG) and visual evoked potentials (VEP) in mice were recorded to evaluate loss of cortical function during the first 30 s after euthanasia by various methods. Tracheal cannulae (for positive-pressure ventilation, PPV) and cortical surface electrodes were placed in mice anesthetized with inhaled halothane. Succinylcholine was used to block spontaneous breathing in the mice, which then underwent continuous EEG recording. Photic stimuli (1 Hz) were presented to produce VEPs superimposed on the EEG. Anesthesia was discontinued immediately before euthanasia. Compared with that obtained before euthanasia, EEG activity during the 30-s study period immediately after euthanasia was significantly decreased after cervical dislocation (at 5 to 10 s), 100% PPV-CO2 (at 10 to 15 s), decapitation (at 15 to 20 s), and cardiac arrest due to KCl injection (at 20 to 25 s) but not after administration of 70% PPV-CO2. Similarly, these euthanasia methods also reduced VEP amplitude, although 100% PPV-CO2 treatment affected VEP amplitude more than it did EEG activity. Thus, 100% PPV-CO2 treatment significantly decreased VEP beginning 5 to 10 s after administration, with near abolition of VEP by 30 s. VEP amplitude was significantly reduced at 5 to 10 s after cervical dislocation and at 10 to 15 s after decapitation but not after either KCl or 70% PPV-CO2 administration. The data demonstrate that 100% PPV-CO2, decapitation, and cervical dislocation lead to rapid disruption of cortical function as measured by 2 different methods. In comparison, 70% PPV-CO2 and cardiac arrest due to intracardiac KCl injection had less rapid effects on cortical function.     

Time-frequency analysis of visual evoked potentials for interhemispheric transfer time and proportion in callosal fibers of different diameters

This study is an extension of the experimental research of Nalçac et al., who presented 16 subjects with a reversal of checkerboard pattern as stimuli in the right visual field or left visual field and recorded EEG at O1, O2, P3, and P4. They applied the chosen bandpass filters (4–8, 8–15, 15–20, 20–32 Hz) to the VEPs of subjects and obtained four different components for each VEP. The first aim of this study is to improve the previous report using some methods in time-frequency domain to estimate interhemispheric delays and amplitudes in a time window. Using the improved estimates of interhemispheric delays, the second aim is to estimate the proportion of callosal fibers of different diameters that are activated by visual stimuli by comparing amplitudes of VEPs in different frequency bands. If the relation between frequency components of VEP and delays for callosal fibers of different dimension were reliable, it would give us an opportunity to deal with amplitude of bandpass-filtered VEPs in order to see approximately the proportion of these fibers activated by a certain stimulus. By using frequency-dependent shifts in time and maximizing the cross correlation of direct VEP (DVEP–VEP obtained from contralateral hemisphere)–indirect VEP (IVEP–VEP obtained from ipsilateral hemisphere) pairs in the time-frequency domain, we examined the delay not only at P100 and N160 peaks but along a meaningful time interval as well. Furthermore, by shifting back the IVEP according to the delay estimated at each time window, both the amplitudes and energies of the synchronized DVEP–IVEP pairs were compared at the chosen frequency bands. The percentages of IVEPs at each band was then examined further in conjunction with the distribution of axon diameters in the posterior pole of the CC, questioning the relation between the distributions of the axon diameters and activations at each band. We established an energy definition to express the activation in the fibers. When the energy percentages of IVEPs in theta and alpha were totaled, they were found to be between 76.2% and 81.6%, which is close to the value 74–77% for fibers of 0.4–1 m in diameter obtained from anatomical study of human CC. The sum of energy percentages in the beta1 and beta2 bands was between 20.1% and 24.2%, which probably reflects the proportion of activation of callosal fibers 1–3 m in diameter.     

Clinical Utility and Limitations of Intraoperative Monitoring of Visual Evoked Potentials

Objectives

During surgeries that put the visual pathway at risk of injury, continuous monitoring of the visual function is desirable. However, the intraoperative monitoring of the visual evoked potential (VEP) is not yet widely used. We evaluate here the clinical utility of intraoperative VEP monitoring.

Methods

We analyzed retrospectively 46 consecutive surgeries in 2011-2013. High luminance stimulating devices delivered flash stimuli on the closed eyelid during intravenous anesthesia. We monitored VEP features N75 and P100 and took patients'' preoperative and postoperative visual function from patient charts. Postoperative ophthalmologic workup was performed in 25 (54%) patients and preoperatively in 28 (61%) patients.

Results

VEP recordings were feasible in 62 of 85 eyes (73%) in 46 patients. All 23 eyes without VEP had impaired vision. During surgery, VEPs remained stable throughout surgery in 50 eyes. In 44 of these, visual function did not deteriorate and three patients (6 eyes) developed hemianopia. VEP decreased transiently in 10 eyes and visual function of all was preserved. VEPs were lost permanently in 2 eyes in two patients without new postoperative visual impairment.

Conclusions

Satisfactory intraoperative VEP monitoring was feasible in all patients except in those with severe visual impairment. Preservation of VEPs predicted preserved visual function. During resection of lesions in the visual cortex, VEP monitoring could not detect new major visual field defects due to injury in the posterior visual pathway. Intraoperative VEPs were sensitive enough to detect vascular damage during aneurysm clipping and mechanical manipulation of the anterior visual pathway in an early reversible stage. Intraoperative VEP monitoring influenced surgical decisions in selected patients and proved to be a useful supplement to the toolbox of intraoperative neurophysiological monitoring.     

Trial on the objective evaluation of visual acuity and its maturation by the method of evoked visual potentials]

We have developed a method to estimate foveal visual acuity (VA) through analysis of VEPs. It consists in determining the smallest check size in a pattern reversal that elicits a significant cortical response. The VEP is regarded as significant if the P 100 amplitude reaches a pre-established level in the signal to noise ratio. A valid criterion to determine normal VEP-VA emerges from the testing of 84 emmetropic and ametropic eyes: within our stimulation and recording conditions, a significant VEP response to the reversal of seven minutes checks corresponds to normal foveal acuity. This criterion has also proved pertinent to discriminate between normal VAs of 20/20 and decreased VAs (20/40 or less) with four other groups of subjects: 14 adult eyes whose VAs of 20/20 are decreased through Bangerter occlusives, 32 emmetropic and ametropic eyes belonging to five-years-olds children, 28 emmetropic and ametropic eyes of twelve-years-olds. In order to guarantee the validity of our results we carried out a double-blind study with ophthalmologists. The relevance of the method we suggest is related to that of the method which consists in extrapolating the regression line between VEP amplitudes and the pattern element sizes. At least we have aimed at establishing VEP norms for the maturation of VA. We have collected data from the following subjects: 5 infants tested monthly between 1 and 6 months, 31 infants ranging in age from 1 to 16 months, 10 five-year-old children, 13 twelve-year-olds, and 11 subjects aged 20. Within our stimulation and recording conditions a significant evoked response to the reversal of seven minute checks can be observed from 8 months onward. With an eight-month-old infant this response to the reversal of seven minute checks cannot be identified to the same response with an adult. There are two major differences: the latency of the major positive component is longer, and the structure of the evoked response consists of fewer components.     

Visual evoked potentials in response to dichoptic presentation of sinusoidal grating and noise background

Dichoptic stimulation was used in comparison of visual evoked potentials (VEPs) with those obtained with monocular stimulation (recordings made from the occipital area). 16 subjects viewed sinusoidal gratings with the right eye while a visual noise was added via a mirror for the left eye. In presence of the noise, amplitude of the early VEP components' N1, P1b, and the late component P2 decreased, P1a is not changed in presence of the noise, and the late negative wave N2 increased for all spatial frequencies. The effect of noise on the amplitude of VEPs obtained for monocular and dichoptic stimulation was similar. The data suggest that external noise is filtered by the V1 cortical neurons--matched filters for the gratings.     

Therapeutic benefit of radial optic neurotomy in a rat model of glaucoma

Radial optic neurotomy (RON) has been proposed as a surgical treatment to alleviate the neurovascular compression and to improve the venous outflow in patients with central retinal vein occlusion. Glaucoma is characterized by specific visual field defects due to the loss of retinal ganglion cells and damage to the optic nerve head (ONH). One of the clinical hallmarks of glaucomatous neuropathy is the excavation of the ONH. The aim of this work was to analyze the effect of RON in an experimental model of glaucoma in rats induced by intracameral injections of chondroitin sulfate (CS). For this purpose, Wistar rats were bilaterally injected with vehicle or CS in the eye anterior chamber, once a week, for 10 weeks. At 3 or 6 weeks of a treatment with vehicle or CS, RON was performed by a single incision in the edge of the neuro-retinal ring at the nasal hemisphere of the optic disk in one eye, while the contralateral eye was submitted to a sham procedure. Electroretinograms (ERGs) were registered under scotopic conditions and visual evoked potentials (VEPs) were registered with skull-implanted electrodes. Retinal and optic nerve morphology was examined by optical microscopy. RON did not affect the ocular hypertension induced by CS. In eyes injected with CS, a significant decrease of retinal (ERG a- and b-wave amplitude) and visual pathway (VEP N2-P2 component amplitude) function was observed, whereas RON reduced these functional alterations in hypertensive eyes. Moreover, a significant loss of cells in the ganglion cell layer, and Thy-1-, NeuN- and Brn3a- positive cells was observed in eyes injected with CS, whereas RON significantly preserved these parameters. In addition, RON preserved the optic nerve structure in eyes with chronic ocular hypertension. These results indicate that RON reduces functional and histological alterations induced by experimental chronic ocular hypertension.     

Visual evoked potentials in the vicinity of the optic tract during stereotactic pallidotomy

We recorded visual evoked responses in eight patients with Parkinson's disease, using a depth electrode either at or below the stereotactic target in the ventral part of the globus pallidus internus (GPi), which is located immediately dorsal to the optic tract. Simultaneously, scalp visual evoked potentials (VEPs) were also recorded from a mid-occipital electrode with a mid-frontal reference electrode. A black-and-white checkerboard pattern was phase reversed at 1 Hz; check size was 50 min of arc. Pallidal VEPs to full field stimulation showed an initial positive deflection, with a latency of about 50 ms (P50), followed by a negativity with a mean latency of 80 ms (N80). The mean onset latency of P50 was about 30 ms. P50 and N80 were limited to the ventralmost of the GPi and the ansa lenticularis. Left half field stimulation evoked responses in the right ansa lenticularis region while right half field stimulation did not, and vice versa. These potentials thus seemed to originate posterior to the optic chiasm. The scalp VEPs showed typical triphasic wave forms consisting of N75, P100 and N145. The location of the recording electrode in the ansa lenticularis region did not modify the scalp VEP. These results suggest that P50 and N80 are near-field potentials reflecting the compound action potentials from the optic tract. Therefore, N75 of the scalp VEPs may represent an initial response of the striate cortex but not of the lateral geniculate nucleus.     

Serial pattern evoked potential recording in a case of toxic optic neuropathy due to ethambutol

Visual evoked potentials (VEPs) were studied in a patient who developed visual impairment during ethambutol treatment. The ERG and the flash VEP were normal at the time of maximal visual loss, whereas pattern reversal VEPs 2 and 5 months after onset revealed evidence of severe bilateral optic nerve involvement, especially affecting macular fibres. Seven months after onset paramacular PNP complexes with a late positivity (scotomatous response) were recorded after pattern reversal and half-field stimulation, suggesting involvement of fibres subserving central vision. At the time when visual acuity was normal there was still electrophysiological evidence of a mild involvement of the anterior visual pathway. The papillomacular bundle seems to be especially involved in ethambutol eye toxicity.     

The conduction of optic nerve fibers using different visual patterns

The Authors have studied the behaviour of checkerboard pattern visual evoked potential (VEP) latencies by using different spatial frequency stimuli and different stimulating visual fields in order to demonstrate whether spatial frequency might constitute a parameter capable of exciting different retinal regions like different stimulus fields. According to the recent literature low spatial frequency stimuli generate VEP with latencies which are significantly shorter than high spatial frequency stimuli, making this method more reliable for the differentiation of macular and peripheral retinal fields.     

Amplitude asymmetry of hemifield pattern reversal VEPs in healthy subjects

The amplitudes of transient and steady-state visual evoked potentials (VEPs) were measured during hemifield stimulation of the left eye in 10 healthy adults. Pattern reversal of a checkerboard was produced at 4 stimulation frequencies: 1, 5, 10 and 15 Hz. The amplitudes of pattern VEPs were evaluated using the paired t test to determine significant differences between right and left hemifields. The transient VEP amplitudes from midoccipital, midparietal, ipsilateral occipital and contralateral occipital electrodes were significantly greater with right hemifield stimulation. The steady-state VEP amplitudes from the midoccipital electrode during 15 Hz stimulation were significantly greater with right hemifield stimulation. Our neurophysiological data may be compatible with neuroanatomical asymmetries of the occipital lobes in humans.     

The temporal frequency response function of pattern ERG and VEP: changes in optic neuritis

Steady-state pattern electroretinograms (PERGs) and visual evoked potentials (VEPs) in response to sinusoidal gratings (2 c/deg), sinusoidally counterphased at closely spaced temporal frequencies (TFs) between 4 and 28 Hz, were recorded from 11 patients with unilateral optic neuritis (ON; 11 affected eyes and 10 healthy fellow eyes) and 7 age-matched normal subjects (7 eyes). Amplitude and phase of responses' second harmonics were measured. Responses' apparent latencies were estimated from the rate at which phase lagged with TF. When compared to control values, mean PERG and VEP amplitudes of ON eyes were reduced (by about 0.4 log units) at both low (5–10 Hz) and high (16–20 Hz) TFs. Mean PERG amplitudes of fellow eyes were selectively reduced at low TFs (by about 0.3 log units). Mean PERG apparent latencies of both ON and fellow eyes were delayed (by 15 and 9 ms, respectively). Mean VEP apparent latency of ON eyes was delayed at both low and high TFs (by 24 and 30 ms, respectively), while that of fellow eyes was selectively delayed at high TFs (by 28 ms). The results in ON eyes indicate non-selective abnormalities of PERG and VEP generators responding at both low and high TFs. VEP TF losses may be in part accounted for by corresponding PERG losses. In the fellow eyes of patients, more selective PERG and VEP TF abnormalities may suggest differential impairment of retinal and postretinal subsystems responding better to low and high TFs (i.e. parvo-and magnocellular streams).