ERGs on the brain: the benefits of simultaneous flash retinal and cortical responses in paediatric cerebral visual impairment

Purpose

To highlight the importance of simultaneous flash electroretinogram (ERG) and visual evoked potential (VEP) recording to differentiate a true flash VEP response from an artefact caused by the intrusion of the ERG on a mid-frontal reference electrode in cases of severe cerebral visual impairment (CVI).

Methods

We report an observational case series of four children with severe CVI who underwent simultaneous flash ERG and VEP recordings. Flash VEPs from Oz–Fz and lower lid skin ERGs referred to Fz were recorded simultaneously to Grass intensity setting 4 flash stimulation.

Results

In all cases, atypical, but reproducible VEPs were evident. Comparison of the timing and waveform of the VEPs and ERGs showed the occipital responses were inverted ERGs and no true flash VEP was evident.

Conclusions

While ISCEV and neurophysiology standards do not require the simultaneous recording of the flash ERG with the VEP, these cases highlight the usefulness of this non-invasive technique particularly in suspected paediatric cerebral visual impairment to differentiate a true VEP from an artefact caused by ERG contamination.

     

A distinctive form of congenital stationary night blindness with cone ON-pathway dysfunction

PURPOSE: To characterize a distinctive form of congenital stationary night blindness (CSNB). DESIGN: Observational case report. PARTICIPANTS: A 30-year-old male with a history of night blindness, several members of his family, a patient with "complete" congenital stationary night blindness (CSNB1), and groups of age-similar control subjects. METHODS: Rod-system function was evaluated by measuring psychophysical dark-adapted thresholds, by recording dark-adapted electroretinograms (ERGs), and by fundus reflectometry. Cone-system function was evaluated by recording light-adapted ERGs, including those to sawtooth flicker, and by recording light-adapted visually evoked potentials (VEPs) to luminance increments and decrements. MAIN OUTCOME MEASURES: Dark-adapted thresholds, ERGs, rhodopsin double densities, Goldmann visual fields, and VEPs. RESULTS: The patient's visual acuity, visual fields, and color vision were normal. His peripheral dark-adapted thresholds were rod-mediated but elevated by approximately 3 log units above normal. Rhodopsin double density and bleaching recovery were normal. His dark-adapted maximal-flash ERG showed a "negative" waveform, in which the b-wave was more reduced in amplitude than the a-wave, although the a-wave amplitude was also reduced. The rod photoreceptors contributed to the patient's dark-adapted ERGs, as illustrated by the unequal responses to cone-matched stimuli. The patient's cone-mediated thresholds for long-wavelength stimuli were within the normal range. However, his light-adapted brief-flash b-wave was abnormal in amplitude and implicit time. Selective abnormalities of the ON responses of the cone system were apparent in the patient's reduced b-wave amplitude to rapid-on flicker with a normal response to rapid-off flicker, and his prolonged VEP latencies to increments but not to decrements. CONCLUSIONS: The overall pattern of findings distinguishes this patient from previously described forms of CSNB. The results suggest that two factors likely contribute to the patient's night blindness: (1) a rod phototransduction defect and (2) a postreceptoral defect. The results also indicate dysfunction within the cone ON pathway.     

An ERG and OCT study of neuronal ceroid lipofuscinosis CLN2 Battens retinopathy

BackgroundLate infantile neuronal ceroid lipofuscinosis (CLN2 Batten disease) is a rare, progressive neurodegenerative disease of childhood. The natural history of motor and language regression is used to monitor the efficacy of CNS treatments. Less is known about CLN2 retinopathy. Our aim is to elaborate the nature, age of onset, and symmetry of CLN2 retinopathy using visual electrophysiology and ophthalmic imaging.Subjects and methodsWe reviewed 22 patients with genetically confirmed CLN2 disease; seventeen showing classical and five atypical disease. Flash electroretinograms (ERGs), flash and pattern reversal visual evoked potentials (VEPs), recorded from awake children were collated. Available fundus images were graded, optical coherence tomography (OCT) central subfoveal thickness (CST) measured, and genotype, age, clinical vision assessment and motor language grades assembled.ResultsERGs show cone/rod system dysfunction preceded by localised macular ellipsoid zone disruption on OCT from 4.8 years. Electroencephalogram (EEG) time-locked spikes confounded both pattern 6/17 (35%) and flash VEPs 12/16 (75%). Paired right eye (RE) and left eye (LE) ERG amplitudes did not differ significantly for each flash stimulus at the p 0.001 level, Wilcoxon ranked signed test. Cone ERGs show a functional deficit before CST thinning in classical disease. Optomap hyper fundus autofluorescence (FAF) at the fovea was noted in three patients with normal ERGs. The oldest patient showed an ovoid aggregate above the external limiting membrane at the fovea, which did not affect the PERG.ConclusionERG findings in CLN2 retinopathy show symmetrical cone-rod dysfunction, from 4y10m in this series, but a broad range of ages when ERG function is preserved.Subject terms: Retina, Neuroscience     

The diagnostic use of the second oscillatory potential in clinical electroretinography

Of all the electroretinogram (ERG) components (a-wave, b-wave, and oscillatory potentials) only one oscillatory potential, OP₂, was found to be significantly correlated with the absolute intensity of the flash stimulus (i.e., the intensity of the stimulus irrespective of the state of retinal adaptation). Our finding was further confirmed in single cell recordings of lateral geniculate unit activity in rabbits in which peak time of OP₂ was found to correlate better with the geniculate activity. For these reasons we have identified OP₂ as the intensity coding oscillatory potential of the ERG. In order to investigate if this new feature could have some clinical significance, we examined photopic ERGs recorded from patients affected with various retinopathies. In most instances the peak time of OP₂ paralleled that of the b-wave, that is, in the ERG with delayed b-wave the peak time of OP₂ was also delayed, while in ERGs with normal b-wave peak time the peak time of OP₂ was also normal. However, in some conditions (especially in cone-rod diseases) a delayed OP₂ was found in ERGs with normal b-wave peak times.     

Cone dysfunction with negative electroretinogram and ring scotoma

Objective: To report an unusual case of cone dysfunction (CD) in which ring scotoma and negative electroretinogram (ERG) were found. Patient and methods: The patient was a 28-year-old Japanese man, who had been aware of an aversion to bright light since the age of eight years.The corrected visual acuity was 0.8 in each eye.Bilateral broad ring scotomas were demonstrated by kinetic perimetry. Almost five degrees of the central visual field were preserved. No nystagmus was noted.The standard full-field scotopic and photopic ERGs were recorded. Results: The photopic ERGs, including bright flash and flicker stimuli under rod-saturating background illumination, showed very little response. Negative ERG, i.e. reduced b-wave amplitude, was evident in the scotopic bright flash ERG.The scotopic responses to dim flashes were within the normal range. Conclusions: On the basis of the ERG findings, the patient was diagnosed as having CD.The central scotomas, usually detected in CD by conventional perimeter, were not found in this patient. Our results suggested that the cone function of this patient was reduced more severely in the parafoveal retina than in the central retina.     

Disturbed visual system function in methionine synthase deficiency

Background Isolated functional methionine synthase deficiency occurs in the cblE and cblG defects of methylcobalamin metabolism and is one of a number of causes of severely elevated plasma homocysteine. Clinical features are predominantly of a neurological nature but also include functional restriction of the visual system manifesting as loss of visual acuity and nystagmus. As yet, the origin and pathogenesis of impaired vision have not been explained.Materials and methods We investigated a patient who was proven by complementation analysis in cultured fibroblasts to belong to the cblG complementation group. Ganzfeld electroretinograms (ERG) and flash visual evoked potentials (VEP) were recorded over a period of 4 years.Results Amplitudes of all International Society for Clinical Electrophysiology of Vision (ISCEV) standard responses were below normal. The greatest reductions were of rod response to 24 V, of standard combined response (SC) b-wave to 120 V, of oscillatory potentials (OP) to 5 V, of cone response b-wave to 35 V, and of 30 Hz flicker response to 8 V. Except for SC and cone a-waves at age 2.5 and 3.5 years, as well as cone b-wave at 3.5 years, amplitudes remained at a subnormal level at follow-up examinations. Implicit times were slightly prolonged (SC b-wave 6 ms, OPs 2 ms, cone b-wave 2 ms, 30 Hz flicker 4 ms) or fell within the normal range. Responses of the flash VEP were severely deformed but reproducible.Conclusions This is the first report of detailed investigations of the visual system in a patient with isolated methionine synthase deficiency. Reduced oscillatory potentials suggest microvascular damage to the retina through homocysteine. Decreased photoreceptor function as well as ganglion cell loss as indicated by pathological flash VEPs may reflect a cytotoxic impact of homocysteine on neurons of the visual pathway.The authors have no competing interestsThe authors have full control of all primary data and they agree to allow Graefes Archives of Clinical and Experimental Ophthalmology to review their data if requested     

Electroretinographic monitoring in birdshot chorioretinopathy

PURPOSE: To evaluate electroretinography (ERG) during long-term follow-up in birdshot chorioretinopathy (BCR). DESIGN: Retrospective, comparative interventional case series. METHODS: SETTING: University subspecialty clinic. PATIENT POPULATION: Twenty-three HLA-A29-positive patients with BCR and 40 normal control subjects. INTERVENTION PROCEDURE: Patients were monitored with ERG approximately annually. Treatment was according to best medical judgment. main outcome measures: Baseline ERG values, vision, and ERG values during observed and treated intervals. RESULTS: Median age of patients was 52 years, and 19 patients were untreated at baseline. Eighty-two ERGs were performed. Eighteen patients had more than one ERG; mean follow-up of these patients was 40.2 months +/- 31.2, median 23 months. At baseline, several ERG parameters were statistically reduced compared with control subjects when adjusted for age. The combined rod-cone and cone b/a wave ratios did not differ from control subjects (P = .45 and 0.14). Scotopic rod and combined rod-cone b-wave amplitudes were statistically correlated with baseline vision, as were implicit times for the combined rod-cone a-wave, cone a-wave, and cone flicker b-wave. Median visual acuity was 20/25 and did not change during follow-up. Most ERG parameters showed marked worsening during observed intervals. During treated intervals, the ERG declined at a rate consistent with aging. CONCLUSIONS: Many ERG parameters in patients with BCR greatly differ from control subjects, correlate with vision, and worsen during observation. Selected patients may show improvement in ERG with treatment. The cone b-wave flicker implicit time was most often associated with clinically important measures such as vision, duration of symptoms, and deviation from normalcy.     

Electroretinograms and visual evoked potentials elicited by spectral stimuli in a patient with enhanced S-cone syndrome

PURPOSE: To evaluate the properties of the retina of a Japanese patient with enhanced S-cone syndrome by analyzing electroretinograms (ERGs) and visual evoked potentials (VEPs) elicited by different spectral stimuli. METHODS: Ganzfeld spectral flashes in the presence of strong white adapting background illumination were used to elicit cone ERGs and VEPs. RESULTS: The cone ERG elicited in the patient by short wavelength stimuli was distinctly different from the normal S-cone ERG. The action spectrum of the cone ERG confirmed its relative hypersensitivity to short wavelengths. The action spectrum of the VEP for the patient showed a similar relative hypersensitivity to short wavelengths. The response of the VEPs to short wavelength stimuli was different in waveform from the VEP response to longer wavelength stimuli observed in a normal subject. CONCLUSIONS: These results indicate that the hypersensitivity to short wavelengths is transmitted to the central nervous system and that there is a short wavelength transducing photopigment in many of the photoreceptors, either abnormal S-cones or photopic rods.     

ERGs,cone-isolating VEPs and analytical techniques in children with cone dysfunction syndromes

Photoreceptor and post-receptoral function in children with congenital and acquired cone disorders was measured by full-field electroretinogram (ERG) and transient visual evoked potentials (VEPs). Subjects were five rod monochromats (RM), five with cone dystrophy (CD), and 30 controls. Patients were diagnosed by clinical findings, ERGs, and standard color vision tests. VEP stimuli were check reversals and color grating onsets that stimulated each photoreceptor type (L-, M-, or S-cones) or post-receptoral pathways (L–M, white/black). VEP signal-to-noise ratios (S/N) were calculated by Fourier analysis of VEP epochs. All RM patients showed extinguished cone ERGs. A near normal S-cone VEP was recorded from a blue-cone rod monochromat without any signal from the L- or M-cone stimuli. Two other RM patients were classified as incomplete RM based on a low-level VEP signal from either L- or M-cone stimuli. CD patients had mildly to severely reduced ERGs and VEPs were abnormal to all cone-isolating stimuli. The VEP S/N ratio was not significantly correlated with the amount of rod contrast in the color stimuli. Color VEPs provide an objective assessment of macular cone function in children with cone dysfunction syndromes that is more sensitive to residual central cone function than standard full-field ERGs. VEP techniques may be useful in the early detection of cone loss in children, especially in children who do not tolerate ERG testing.     

综合视觉电生理检测对白内障术后视功能恢复的评估

目的 评价术前综合视觉电生理检测在判断白内障手术视功能预后中的作用。方法 白内障患者３１５例（４０８眼）术前常规检测图形翻转视觉诱发电位（ＰＶＥＰ）、红蓝光视网膜电图（ＦＥＲＧ）和视网膜电图的振荡电位（ＯＰｓ）。正常对照组１６２例（２６６眼）。术后检查眼底,术后３ｍｏ查矫正视力。结果 术后矫正视力≥０．５（Ⅰ组）和〈０．５（Ⅱ组）者与对照组相比,术前ＰＶＥＰ的Ｐ１００波振幅均下降、潜伏期均延长,后     

Retinal pathway origins of the pattern ERG of the mouse

This study investigated contributions from the retinal On and Off pathways, and the spiking and nonspiking activity of neurons in those pathways to the pattern ERG of the mouse. Light-adapted pattern and ganzfeld ERGs were recorded from anesthetized C57BL/6 mice 3-4 months of age. Recordings were made before and after intravitreal injections of PDA (cis-2,3-piperidine-dicarboxylic acid) to block transmission to hyperpolarizing 2nd order and all 3rd order neurons, TTX (tetrodotoxin) to block Na⁺-dependent spiking, APB (2-amino-4-phosphonobutyric acid) to block synapses between photoreceptors and ON-bipolar cells, and APB + TTX and PDA + TTX cocktails. The pattern stimuli consisted of 0.05 cy/deg gratings reversing in contrast at 1 Hz, presented at various contrasts (50-90%) and a rod saturating mean luminance. For flash ERGs, brief green ganzfeld flashes were presented on a rod-suppressing green background. Recordings were made 39-42 days after unilateral optic nerve crush (ONC) in a subset of animals in which ganglion cell degeneration was subsequently confirmed in retinal sections. Pattern ERGs were similar in waveform for all contrasts, with a positive wave (P1) peak for 90% contrast around 60 ms on average and maximum trough for a negative wave (N2) around 132 ms after each contrast reversal; amplitudes were greatest for 90% contrast which became the standard stimulus. ONC eliminated or nearly eliminated the pattern ERG but did not affect the major waves of the flash ERG. PDA and TTX both delayed P1 and N2 waves of the pattern ERG, and reduced their amplitudes, with effects of PDA on N2 greater than those of TTX. In the flash ERG, PDA reduced a-wave amplitudes, removed OPs but hardly affected b-wave amplitudes. In contrast, TTX reduced b-wave amplitudes substantially, as previously observed in rat. APB removed P1 of the pattern ERG, but left a negative wave of similar timing and amplitude to N2. In the flash ERG, APB removed the b-wave, producing a negative ERG. Addition of TTX to the APB injection removed most of N2 of the pattern ERG, while other waves of the pattern and flash ERG resembled those after APB alone. Addition of TTX to the PDA injection had little effect on the pattern ERG beyond that of PDA alone, but it prolonged the b-wave of the flash ERG. In conclusion, this study confirmed that a selective lesion of ganglion cells will practically eliminate the pattern ERG. The study also showed that P1 of the mouse pattern ERG is dominated by contributions, mainly spiking, from ON pathway neurons, whereas N2 reflects substantial spiking activity from the OFF pathway as well as nonspiking contributions from both pathways.     

Night Blindness with Depolarizing Pattern of ON/OFF Response in Electroretinogram: A Case Report

Purpose: To present a patient who has night blindness with a depolarizing pattern of ON/OFF response by electroretinography (ERG). Case: A 43-year-old woman had had night blindness and poorly corrected visual acuity since childhood. Parental consanguinity was noted. The patient had suffered from mental retardation, epilepsy, and mild cerebellar ataxia. Corrected visual acuity was 20/30 in the right eye and 20/25 in the left. Goldmann perimetry showed no scotoma but slight depression with internal isoptors. No evidence for rod activity was observed by Goldmann–Weekers adaptometry. The ocular fundi appeared normal. Methods: Conventional full-field ERGs to scotopic (dim and bright flash) and photopic (bright flash and flicker) stimuli were recorded. Photopic ERG responses to long flash stimulation (200 ms) were also examined. Results: The scotopic responses to dim flash were non-recordable, while those to bright flash were severely reduced. The photopic responses to bright flash were decreased. The amplitudes of flicker responses also were significantly decreased, and the implicit times of those responses were prolonged. Although the amplitudes of a- and d-waves to long flash stimulation were reduced, those of the b-wave were within normal range. The implicit times of a-, b- and d-waves were significantly prolonged. The patient showed a normal rise for the photopic b-wave but lacked a normal falling slope after the b-wave peak. An OFF-response late-negativity was also noted. Conclusions: The abnormal ON/OFF response found in the patient could be diagnosed as depolarizing pattern, characterized by elevation of the plateau to a positive potential above the prestimulus baseline. Since the ERG waveforms and clinical features found in our patient were different from those in previous reports, her ERG findings might reflect another retinal physiological mechanism.     

ISCEV Standard for full-field clinical electroretinography (2008 update)

This document, from the International Society for Clinical Electrophysiology of Vision (ISCEV), presents an updated and revised ISCEV Standard for clinical electroretinography (ERG). The parameters for flash stimulation and background adaptation have been tightened, and responses renamed to indicate the flash strength (in cd·s·m⁻²). The ISCEV Standard specifies five responses: (1) Dark-adapted 0.01 ERG (rod response); (2) Dark-adapted 3.0 ERG (combined rod–cone response); (3) Dark-adapted 3.0 oscillatory potentials; (4) Light-adapted 3.0 ERG (cone response); (5) Light-adapted 3.0 flicker (30 Hz flicker). An additional Dark-adapted 10.0 ERG or Dark-adapted 30.0 ERG response is recommended.

Establishing baseline rod electroretinogram values in achromatopsia and cone dystrophy

Purpose

To establish the normal range of values for rod-isolated b-wave amplitudes in achromatopsia and cone dystrophies.

Methods

We reviewed charts of 112 patients with various types of cone dystrophy, and compared their standardized electroretinographic rod b-wave amplitudes with age-matched normal controls. Twenty-six patients had known mutations in achromatopsia and cone dystrophy genes, while 53 were characterized by their inheritance pattern since they had yet to have their gene identified. Visual acuity information and scotomata were documented.

Results

We found that patients with achromatopsia and cone dystrophy had rod b-wave amplitudes that were significantly lower than age-matched controls, but found no evidence of rod amplitude progression nor loss of peripheral visual fields in the study group.

Conclusions

We found that cone dystrophy patients of all types had depressed rod-isolated ERGs across the board. If typical diagnostic criteria are used, these patients might be considered to have ??abnormal?? rod-isolated electroretinographic values, and might be called ??cone-rod dystrophy??, even though the waveforms are stable for years. Patients with cone-rod dysfunction patterns on ERG can be better understood by also performing kinetic (Goldmann) visual fields, which will help to distinguish cone dystrophies from progressive cone-rod dystrophies by central scotomata size and progression over time in many forms of cone-rod dystrophy.     

The 52nd ISCEV International Symposium Abstract Issue

Purpose

We have monitored retinal function in patients treated for retinoblastoma (primarily, but not exclusively by intra-arterial chemotherapy infusion) by electroretinography (ERG) recordings for the past 7 years. We here present data from 599 ERG studies of 108 patients, in which a complete ERG protocol including both photopic and scotopic recordings was performed, in justification of our frequent practice of reporting primarily 30-Hz photopic flicker amplitude data.

Methods

Patients referred for treatment of retinoblastoma underwent ERG recordings during examination under anesthesia whenever possible: at baseline and following most treatment sessions. Correlations were calculated for the complete datasets between the four primary amplitude response parameters: photopic single flash b-wave, photopic 30-Hz flicker peak-to-trough, scotopic rod-isolating b-wave, and scotopic maximal flash b-wave.

Results

Using our adaptation of the International Society for Clinical Electrophysiology of Vision-recommended standard ERG protocol, ERG responses of eyes of patients with untreated retinoblastoma or following traditional or intra-arterial treatment for retinoblastoma show very high correlations between 30-Hz flicker amplitude responses and three other standard photopic and scotopic ERG response amplitudes. Reductions in ERG amplitudes seen in these eyes following treatment show no significant difference between retinal dysfunction estimated using rod- or cone-dominated responses.

Conclusion

These observations support the use of photopic response amplitudes (especially in response to 30-Hz flicker) as the primary ERG outcome measure in studies of treated and untreated eyes with retinoblastoma when more complete ERG protocols may be impractical.     

PIII and Derived PII Analysis in a Patient with Retinal Dysfunction with Supernormal Scotopic ERG

Purpose: To present electroretinographic (ERG) findings in a patient with retinal dysfunction with supernormal scotopic ERG, and to analyze rod and cone PIII components and rod inner nuclear layer (derived PII) responses. Patient: A Japanese 11-year-old girl complained of poor visual acuity. There was no parental consanguinity in her family. The corrected visual acuity was 0.7 in both eyes. No abnormal finding was observed in both fundi. Methods: The patient underwent full-field ERGs. Rod and cone a-waves were analyzed using photoreceptor models. The derived PII responses were analyzed using a technique described by Hood and Birch. Results: In the photopic ERG, responses to single flash and 30-Hz flicker were attenuated. In the scotopic ERG, b-wave was supernormal in amplitude in response to intense flashes, but smaller than normal and markedly delayed over a lower range of flash intensities. By the PIII analysis, phototransductions (values of S) of both rod and cone were remarkably decreased. The derived PII responses for this patient were larger than the responses for normal subjects, and the onset of the PII responses in this patient are significantly delayed compared to those in normal subjects. Conclusions: The ophthalmological findings in this patient are consistent with previous publications of this disease. Although it has been reported that the sites of disease action were beyond the outer segment (values of S were within the normal range), our results suggest that photoreceptors could be involved in sites of disease action in at least some patients with this disease.     

Correlation of electroretinographic and fluorescein angiographic findings in unilateral central retinal vein obstruction

Background: In central retinal vein obstruction (CRVO), electroretinogram (ERG) abnormalities and extensive retinal capillary dropout (CD) in the fluorescein angiogram (FA) are good indicators of retinal ischemia. We retrospectively studied patients with unilateral CRVO and compared the ERG and FA results Methods: Single white flash ERG, photopic ERG, scotopic ERG and flicker ERG were recordered in 30 cases of unilateral CRVO. We analyzed the correlation between the ERG results and the presence/absence of extensive CD Results: The ERG b/a-wave amplitude ratios, photopic and scotopic b-wave amplitudes, and flicker amplitudes were significantly smaller (P<0.05) in eyes with extensive CD (n=12, 40%), than in eyes without (n=18, 60%). When the photopic or scotopic b-wave amplitudes were normal or supernormal, extensive CD on FA was absent in all eyes. When the b/a-wave ratios were 1.0 or when the b-wave amplitudes with white flash or flicker amplitudes were normal or supernormal, extensive CD was present in less than 32% of eyes Conclusion: These results suggest that the ERG results, especially the b/awave amplitude ratio, are significantly correlated with the presence/absence of CD on FA in CRVO.     

Cone and rod ERGs in degenerations of central retina

Sixty-four patients with retinal degenerations at the posterior pole were reviewed and their ERGs analysed. On the basis of symptoms, visual acuity, ophthalmoscopy and cone/rod ERG the patients were divided into five diagnostic groups: Stargardt's disease, fundus flavimaculatus, cone degeneration, dominant drusen and central retinitis pigmentosa (RP). Stargardt's disease and fundus flavimaculatus show low-normal or subnormal cone b-wave amplitudes, often with prolonged peak times; the rod ERG is rarely abnormal. Cone degeneration presents with reduced visual acuity, photophobia, nystagmus and minimal fundus changes. The ERG shows severely reduced cone b-waves and increased peak times; the rod b-waves are in the low-normal or subnormal range. Dominantly inherited drusen, included for comparison, revealed little change in the ERG in spite of widespread ophthalmoscopic changes: b-wave amplitudes fall mostly in the low-normal range, and their peak times may be prolonged. RP of the central type reveals considerable variability in all clinical aspects, but the cone and rod ERGs are consistently greatly reduced, showing markedly increased peak times of the cone b-waves. Recording of the Ganzfeld ERG with cone/rod separation thus proves useful in differentiating degenerations of the central retina.     

Simultaneous electroretinograms and visually evoked potentials from adult amblyopes in response to a pattern stimulus.

Electroretinograms (ERGs) and visually evoked potentials (VEPs) were recorded simultaneously from each eye of three adult amblyopes. A spatially alternating checkerboard pattern stimulus of constant mean luminance was used to eliminate the effect of stray light on the ERG. The VEP was affected in the amblyopic eye of all subjects. In two subjects the VEP amplitude was reduced; in the third subject the amplitude was not attenuated, but the waveform of the VEP was markedly altered. Photopic ERGs recorded from the normal and amblyopic eye of each subject with an unpatterned flashing light were equal in amplitude. However, ERGs elicited by a patterned stimulus were affected in the amblyopic eye of all three subjects; the after-potential showed larger reductions in amplitude than the b-wave. These results suggest there may be some retinal involvement in human amblyopia.     

Dose-dependency and Time-course of Electrophysiologic Short-term Effects of VIAGRA®: A Case Study

The dose-dependency and time-course of the short-term visual effects of sildenafil citrate (VIAGRA) were tested in two subjects. Blood pressure was measured and samples of blood taken at 30 min intervals before and after drug administration. In the first experiment, prolongations of the implicit times of the scotopic maximum a-wave, cone a- and b-wave, 33 Hz flicker, ON-response a- and b-wave and 3.3 Hz a- and b-wave electroretinogram (ERG) recordings and of the oscillatory potentials OP1, OP2, and OP3 were observed for both eyes of both subjects, following 100 or 200 mg dosings. Interestingly, no prolongation was found for OP4, to which the OFF-bipolar cell pathway significantly contributes. In the second experiment, in which visual function was repeatedly assessed following a 200 mg dose, similar prolongations were found in both eyes of one subject for the implicit times of the oscillatory potential OP2, the cone b-wave response and the 3.3 Hz a-wave. Moreover, the steady-state (A0) and immediate extinction (B0) blue target thresholds of transient tritanopia were raised relative to the pre-drug administration baseline effects. While the maximum lowering of both systolic and diastolic blood pressure approximately correlated with the peak plasma concentration of sildenafil (c. 30-60 min after administration), the peak magnitudes of most visual effects were found at c. 110 min, consistent with a second compartment kinetic.