Visual field constriction and electrophysiological changes associated with vigabatrin

Purpose: We investigated functional, morphological and electrophysiological changes in patients under anti-epileptic therapy with vigabatrin (VGB), a GABA aminotransferase inhibitor. Methods: 20 epileptic patients treated with vigabatrin (age range 25–66 years) were enrolled in this study. The referrals were made by the treating neurologist, based on suspected or known visual field changes in these patients. Two patients had vigabatrin monotherapy, 18 patients were treated with vigabatrin in combination with other antiepileptic drugs. None of the patients reported visual complaints. Patients were examined with psychophysical tests including colour vision (Farnsworth D15), dark adaptation threshold, Goldmann visual fields and Tuebingen Automated Perimetry (90°). A Ganzfeld ERG and an EOG following the ISCEV standard protocol were also obtained. Additionally, all patients were examined with the VERIS multifocal ERG including recordings of multifocal oscillatory potentials. Results: Visual acuity, anterior and posterior segments, colour vision and dark adaptation thresholds were normal in all patients. Of 20 patients, 18 presented visual field constriction. All patients with visual field defects revealed altered oscillatory potentials waveforms in the ERG, especially in those patients with marked visual field defects. Multifocal oscillatory potentials were also delayed in those patients. In some patients a delayed cone single flash response (6/20), a reduced mERG amplitude (12/20) and a reduced Arden ratio (9/20) were found. Conclusions: The present data indicate an effect of vigabatrin on the inner retinal layers. Since abnormalities of the oscillatory potentials were seen in all patients with visual field defects a dysfunction of GABA-ergic retinal cell transmission might be assumed.     

Visual electrophysiological effect of a GABA transaminase blocker

Vigabatrin is an antiepileptic drug for the treatment of partial seizures. The anticonvulsant effect is achieved by irreversible inhibition of the enzyme GABA-transaminase which catalyses the inactivation of GABA. Vigabatrin has been associated with visual field loss and electrophysiological abnormalities. The purpose of the study was to determine any alterations in normal volunteers of the visual field and the visual electrophysiology resulting from a short exposure to vigabatrin. A three-way, double-blind study of placebo, carbamazepine and vigabatrin was undertaken at baseline and on days two, four and nine. Seven subjects completed all three cycles and 14 subjects (six females and eight males; mean age 27.3 years SD 6.7) completed at least one cycle. Static threshold automated perimetry comprised Humphrey Visual Field Analyzer Programs 30-2 and 30/60-2. Electro-oculography and electroretinograms were performed with undilated pupils using the Medelec Ganzfeld stimulator GS2000. The visual field was unaffected by placebo, carbamazepine or vigabatrin. The group mean amplitudes and latencies for the scotopic ERG, 30Hz flicker ERG and the oscillatory potentials remained unchanged for any cycle. The group mean photopic ERG b-wave latency increased from baseline (p < 0.05); no significant change occurred with carbamazepine or placebo. The group mean Arden Index for vigabatrin decreased from baseline to day 9 (p <; 0.01); no significant differences were present for carbamazepine or placebo. Vigabatrin has a rapid effect on both the photopic ERG and the EOG; however, the changes merely reflect alterations in retinal GABA levels secondary to concomitant blocking of GABA transaminase by existing vigabatrin therapy. This revised version was published online in July 2006 with corrections to the Cover Date.     

The value of electrophysiology results in patients with epilepsy and vigabatrin associated visual field loss

PURPOSE: To determine the value of electrophysiological findings in patients with temporal lobe epilepsy and to relate these findings to the amount of concentric contraction of the visual field and the use of vigabatrin. METHODS: Electro-retinograms and electro-oculograms were done on 30 patients, operated for temporal lobe epilepsy. The patients were divided into three groups: (A) concentric contraction of the visual field associated with a history of vigabatrin medication (15 patients), (B) normal visual field with vigabatrin use (11 patients) and (C) normal visual field without vigabatrin medication (4 patients). RESULTS: Electrophysiological abnormalities were found in 50% of the patients in group A. The Arden ratio of the EOG was lowered in 57%. Abnormalities in the ERG were found: b-wave implicit time photopic F was prolonged (50%), b-wave amplitudes scotopic B (53%), C (73%) and G (50%) and photopic H (50%) were diminished. The amount of visual field loss and the total dose of vigabatrin used, showed only slight correlation with the ERG and EOG. The use of vigabatrin during the ERG and EOG recording in group A, gave a higher b-wave amplitude scotopic G in 64% of cases. The a-wave implicit times scotopic G (73%) and photopic G (59%) and H (73%) were shortened in group B. CONCLUSION: EOG was abnormal in 57% in group A. ERG abnormalities could only be found in 50% of group A, mainly in the inner retina. Since also the total dose of vigabatrin and the amount of visual field loss did not really show a correlation with the electrophysiological findings and results of literature are not unanimous, electrophysiology does not appear at present to be a good method to detect patients with, or at risk of, vigabatrin associated visual field loss. Regularly performed visual field examination remains the cornerstone in screening.     

Electro-ophthalmological recovery after withdrawal from vigabatrin

This study describes the effects of stopping of the anti-epileptic drug vigabatrin on the visual field and electrophysiological changes in one third of the group of patients which is described in the paper `Visual field and electrophysiological abnormalities due to vigabatrin' (Van der Torren and Graniewski, 2002). In 1997 several reports described the possible oculotoxic effect of vigabatrin followed by a reconsideration of this medication in epileptic patients. Vigabatrin was discontinued in one-third of the patients on chronic medication (mean duration 4.8 years). The visual field and electrophysiological examinations were repeated every 3 months if possible, otherwise at 6-month intervals. The EOG Arden index and the ERG rod b-wave showed a significant improvement when vigabatrin was discontinued. Repeated examinations of visual fields and electrophysiology shortly after discontinuation of the drug (between 1 and 3 months) and later on after 6 months and 1 year showed a recovery of the EOG Arden index and the ERG rod b-wave during this period. The visual fields did not change in either direction. Conclusion: the recovery effect is a strong argument for the hypothesis that the reduction in EOG and ERG b-wave is an oculotoxic effect. The electrophysiological improvement during 6 months or longer after discontinuation and the unchanged visual fields are an argument for the hypothesis that the visual field represents the irreversible intoxicating effect on the retina, whereas the electrophysiology represents a more direct effect on the retinal glial cells level.     

Vigabatrin: longterm follow-up of electrophysiology and visual field examinations

BACKGROUND: To report the results of repeated electrophysiological and visual field examinations in patients with vigabatrin-associated visual field loss (VGB-VFL) and the relationship between these electrophysiological findings, the cumulative dose of vigabatrin and the extent of visual field loss. METHODS: Twenty-two eyes of 11 patients with VGB-VFL were studied. All patients underwent surgery for therapy-resistant epilepsy. Repeated electro-oculograms (EOGs) and flash electroretinograms (ERGs) were made and the cumulative dose of vigabatrin and the visual field loss were recorded after a period of 37-47 months. RESULTS: The visual field loss was stable in patients who had stopped vigabatrin at the time of the first examination. There was a slight increase in VFL in patients who continued vigabatrin. During the second EOG and ERG, abnormalities in scotopic and photopic a-wave latencies and in scotopic b-wave amplitude were found in more than 50% of patients. Only b-wave latency became normal, while EOG, a-wave latency, a-wave amplitude and b-wave amplitude stayed abnormal. The amount of VFL and the cumulative dose of vigabatrin were statistically correlated with the b-wave amplitude, mainly photopic, found during the first and second examinations. CONCLUSION: After 4 years, EOG, flash ERG and visual field loss had not improved in patients with VGB-VFL. The statistically significant correlation found during the first examination between the amount of VFL and the cumulative dose of vigabatrin with the (mainly photopic) b-wave amplitude remained constant.     

Reduced full-field electroretinogram (ERG) in a patient treated with methotrexate

PURPOSE: To examine retinal function in a patient with decreased vision possibly due to treatment with methotrexate. METHODS: Ophthalmological examination included testing of visual acuity (VA), fundus inspection, fundus photography, and kinetic perimetry. Retinal function was tested objectively with three electrophysiological methods: full-field electroretinography (ERG), multifocal electroretinography (mfERg) and also electro-oculography (EOG). RESULTS: A 13-year-old boy with psoriasis arthritis had been treated with methotrexate on a weekly basis for 8.5 years. After terminating treatment, his VA, which was reduced to 0.3 in both eyes initially, improved during the following 3 years but did not return to normal. No visual field defects were found with kinetic perimetry. The rod and cone responses in the full-field ERG were markedly reduced in b-wave amplitude initially, but grew slowly to nearly normal values 3 years later. After withdrawal of the drug, the mfERG demonstrated normal responses in the macular region. The Arden index in the EOG was normal. CONCLUSION: Chronic treatment with methotrexate may affect VA, and mat reversible reduce rod and cone function. In patients who use systemic medication and who vision is reduced, objective evaluation of retinal function with electrophysiological methods is recommended.     

服用羟氯喹者的视觉电生理检查

目的 对服用羟氯喹者进行视网膜电图和眼电图检查,评价用药安全性.方法 选择正在服用羟氯喹的180例自身免疫病患者,行视力、眼压、眼前节及散瞳眼底检查,其中55例患者行视网膜电图和眼电图检查.每6个月复诊1次.结果 180例患者的视力、眼压、眼底均正常,55例患者按用药时间分组,各用药时段组Arden比、a波、b波峰时和a波平均振幅及30 Hz反应差异均无统计学意义(P>0.05),而在用药13～24月组,-15dB光刺激强度下的b波平均振幅较未用药组和用药3～12月组差异均有统计学意义(P<0.05).结论 使用低剂最的羟氯喹具有良好的眼部安全性.     

Attenuation of the retinal nerve fibre layer and reduced retinal function assessed by optical coherence tomography and full‐field electroretinography in patients exposed to vigabatrin medication

Purpose: To investigate the clinical value of assessment of peripapillary retinal nerve fibre layer (RNFL) thickness with OCT in addition to the evaluation of retinal function measured by full‐field electroretinography (ff‐ERG) in patients with suspected vigabatrin (VGB)‐attributed visual field defects. Methods: Visual fields from adult patients in our clinical follow‐up program for VGB medication were analysed. Twelve patients with suspected VGB‐attributed visual field defects were selected for the study. They were re‐examined with computerized kinetic perimetry, ff‐ERG and OCT (2D circle scan). Results: Constricted visual fields were found in all patients. Comparative analysis of ff‐ERG parameters showed reduced b‐wave amplitudes for the isolated and the combined rod and cone responses (p < 0.0001). The a‐wave, reflecting photoreceptor activity, was reduced (p = 0.001), as well as the summed amplitude of oscillatory potentials (p = 0.029), corresponding to inner retinal function. OCT measurements demonstrated attenuation of the RNFL in nine of 12 patients, most frequently superiorly and/or inferiorly. No temporal attenuation was found. Significant positive correlations were found between the total averaged RNFL thickness, superior and inferior RNFL thickness and reduced ff‐ERG parameters. Positive correlations were also found between RNFL thickness and isopter areas. Conclusion: OCT measurements can detect attenuation of the RNFL in patients exposed to VGB medication. RNFL thickness correlates with reduced ff‐ERG parameters and isopter areas of constricted visual fields, indicating that VGB is retino‐toxic on several levels, from photoreceptors to ganglion cells. The study also supports previous studies, suggesting that OCT measurement of the RNFL thickness may be of clinical value in monitoring patients on vigabatrin therapy.     

Visual field and electrophysiological abnormalities due to vigabatrin

The purpose of this study was to determine the electrophysiological changes in patients using the anti epileptic drug vigabatrin and to correlate these findings with the previously reported risk for visual field loss in these patients. In 1998 the neurologists of both involved hospitals referred all patients on vigabatrin medication for ophthalmological examination to the outpatients clinics. Of the 33 patients whom were referred to our outpatient clinics, four had to be dropped from the study because of disability to perform the examinations the remaining 29 patients were included in the study. Standard ophthalmological investigations were carried out, and contrast sensitivity, visual field (Humphrey 30-2 and Esterman or Octopus 32), colour vision (panel D15), ERG and EOG according to ISCEV standards were tested. 18 patients continued the medication and 11 stopped taking the drug during the study. Nine of the patients who stopped the drug were followed during at least half a year afterwards, this group will be described in the combined article `Electro ophthalmic recovery after withdrawal from vigabatrin' (Graniewski and Van der Torren, this issue). The electro-ophthalmological findings in the group of 29 patients were correlated with the visual fields and the daily and cumulative dosages of vigabatrin. Of the patients, 32% showed no visual field constriction at all; from these patients 64% had EOG and/or ERG changes. Of the patients with slight to marked visual field constriction, 90% presented EOG and/or ERG changes. Significant correlation between daily dosages of vigabatrin and visual field defects was shown as well as between visual field defects and rod and cone b wave amplitude reductions. Cumulative vigabatrin dosages presented a significant correlation with EOG ratio and ERG rod b-wave amplitude. Conclusively EOG and ERG testing were found to be even an more accurate way to monitor the direct vigabatrin effect on the outer retina and is possible different from the visual field testing.     

Electroophthalmological characteristics in ischemic retinopathy (author's transl)]

In the ERG the b-wave and the oscillatory potentials are reduced or nonrecordable in ischemic retinopathy. The photopic b-wave appeared to be more sensitive than the scotopic b-wave. In the EOG the slow oscillation is reduced. These clinical observations are in accordance with the results of experimental studies in rhesus monkeys.     

The function of eye and vision system in children and youth treated with vigabatrin--our own experiences

PURPOSE: The aim of this study is to find the relationship between visual function changes and vigabatrin treatment continuation or discontinuation. MATERIAL AND METHODS: 19 patients (11 males, 8 females) from 8 to 20 years old, treated with vigabatrin because of partial epilepsy, were examined. Best corrected visual acuity, contrast sensitivity and static visual field were done. The examinations were repeated after 1-2 months and after 1-2 years. The longest follow-up was about three years (one girl). In some children from this group additional elctrophysiologic tests (ERG, EOG according to ISCEV standards), were done. RESULTS: Corrected visual acuity was 5/5 in all eyes. Contrast sensitivity was normal and it was not changed in follow-up period. Abnormal visual field was found in more than half of examined patients. The improvement of visual field occurred after vigabatrin discontinuation, but in one patient the improvement occurred although vigabatrin treatment was continued. Most of the patients refused control ERG and EOG, but in first examination decreased or border b-wave amplitude after "flicker 30Hz" was found. CONCLUSIONS: In some patients treated with vigabatrin reversible visual field changes occurred. Multicentre study should be performed, to solve the problem of relationship between visual field changes, vigabatrin and other antiepileptic treatment. All tests in group of epileptic patients are difficult because of poor cooperation.     

Retinal Function in Rabbits Does Not Improve 4–5 Months after Terminating Treatment with Vigabatrin

Purpose: We have previously reported changes in retinal function and histopathology in rabbits treated with vigabatrin. The purpose of the present study was to evaluate retinal function and histopathology of retina in rabbits 4–5 months after terminating vigabatrin medication. Methods: Five rabbits were treated with a daily per oral dose of vigabatrin during 12–13 months. After terminating treatment an observation period of 4–5 months followed. Six rabbits receiving water served as controls. Standardized full-field electroretinograms were performed every 6–8 weeks, using a Burian–Allen bipolar contact lens. After 18 months the rabbits were sacrificed and the morphology of the sectioned retina was studied. The antibodies used for staining were GABA, GFAP, GAD, and vimentin. Results: After 12–13 months of treatment the full-field ERG was reduced in all rabbits treated with vigabatrin. There was a statistically significant difference in the dark adapted cone b-wave amplitude between treated animals and controls (Wilcoxon signed-rank test, p = 0.043). This difference was consistent also 4–5 months after terminating treatment. Immunohistology of the sectioned retina demonstrated no significant difference in immunoreactivity between treated animals and controls. All treated rabbits demonstrated elevated serum concentration of the drug during medication. Conclusion: Four to five months after terminating treatment with vigabatrin the rabbit full-field ERG remains reduced in isolated cone b-wave amplitude indicating that vigabatrin induced retinal dysfunction may be irreversible. However, immunohistology is normal after a period without treatment, implying that the previously described changes in retinal morphology and glial cell activity are reversible, and probably exist only during treatment.     

Full-field ERG and visual fields in patients 5 years after discontinuing vigabatrin therapy

Purpose In numerous studies vigabatrin medication has been associated with visual field constriction and alterations in the full-field electroretinogram (ff-ERG), but it is not clear whether these changes are reversible or not. The purpose of this study was to examine patients with visual field loss and reduced ff-ERG several years after discontinuing vigabatrin therapy, in order to investigate reversibility. Methods Eight patients with visual field constriction and reduced cone responses measured by 30 Hz flicker ERG were examined with Goldmann perimetry and ff-ERG 4-6 years after discontinuing medication. The results were compared with investigations conducted during medication, 4-6 years previously. Statistical analysis was also used to compare the ff-ERG results of the patients, during treatment and at follow-up, with a group of 70 healthy subjects. Results Visual field constriction remained 4-6 years after discontinuing vigabatrin therapy. The amplitude of the 30 Hz flicker response also remained reduced on follow-up both compared with the results during treatment and with the control group. Moreover, the amplitude of the isolated rod response and the combined rod-cone response were decreased in the patients compared with the control group, during vigabatrin treatment as well as on follow-up. On follow-up, oscillatory potentials (OPs) also were registered, showing reduced amplitudes in patients compared with controls. The within subject comparison showed no significant changes. Conclusion Vigabatrin attributed visual field constriction and reduced ff-ERG responses remain several years after discontinuing vigabatrin therapy, indicating drug-induced permanent retinal damage.     

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.     

Symptomatic and asymptomatic visual loss in patients taking vigabatrin.

PURPOSE: To investigate the clinical, perimetric, and electrophysiologic findings in patients with visual field loss on long-term treatment with the antiepileptic medication vigabatrin. DESIGN: Consecutive observational case series. PARTICIPANTS: Forty-one consecutive subjects taking vigabatrin referred for screening ophthalmologic assessment were studied. Twelve subjects with evidence of peripheral visual field constriction are presented. METHODS: Twelve subjects with evidence of peripheral visual field constriction on 60-4 perimetry underwent central 30-2 and blue-on-yellow (B/Y) perimetry, as well as electroretinography (ERG), electro-oculography (EOG), and visual-evoked potential (VEP) testing. MAIN OUTCOME MEASURES: Visual acuity; fundus abnormalities; visual field loss; and ERG, EOG, or VEP abnormalities were the main outcome measures. RESULTS: Eight of the 12 subjects with constricted visual fields were asymptomatic. The central 30-2 perimetry demonstrated bilateral visual field constriction in 9 of 12 patients and the B/Y perimetry in 8 of 9 patients tested. Of the ten patients tested electrophysiologically, four had abnormal ERGs, five had abnormal EOGs, and three had delayed VEPs. CONCLUSIONS: The incidence of visual field constriction in patients taking vigabatrin may be higher, and asymptomatic visual field loss more common, than reported previously. The authors postulate a possible Muller cell dysfunction in the peripheral retina. Patients taking vigabatrin should have regular peripheral visual field examinations.     

Carotinoid retinopathy. II. Electrophysiologic findings in 23 carotenoid-treated patients

Twenty-three patients on long-term therapy (up to 14 years) with carotenoids (up to 336 g) were tested electrophysiologically. The EOG revealed a small but not significant delay of the light peak. Arden's ratio, however, was normal. The ERG was depressed as far as photopic activity was concerned. At low dosages of carotenoids the scotopic ERG amplitudes were found to be hypernormal, whereas at higher dosages the increase in amplitude during dark-adaptation was markedly delayed. There was a dose-dependent prolongation of b-wave implicit time and a dose-dependent reduction in oscillatory potentials. The marked effect on the b-wave and on the oscillatory potentials and the site of the retinal crystals permit the assumption that a mechanism of carotenoid action is located in the middle layers of the retina.     

The effect of metoclopramide on the Ganzfeld electroretinogram

Antecedent light flashes enhance the amplitude of the electroretinogram (ERG) oscillatory potentials, but do not modify other ERG responses nor dark-adaptation sensory thresholds. Metoclopramide infusion (i.v.) has a generally attenuating effect on the ERG, which is more evident under conditions of dark- than light-adaptation. Metoclopramide decreases the peak amplitude of the rod b-wave and the dark-adapted cone b-wave in a similar manner; it also significantly increases the implicit time of the rod b-wave, but not of the dark-adapted cone b-wave. In addition metoclopramide reverses the enhancement of the oscillatory potentials by the antecedent light flashes.     

电生理测试作为早期青光眼诊断指标的横断面研究

明视负向反应(PhNR)和图形视网膜电图(PERG)的结果作为评估青光眼的诊断指标.10例对照组和15例早期青光眼患者接受了完整的眼科检查,包括视力测量,眼压(IOP)测量,眼底检查和视野检查.同时进行图形视网膜电图和全视野视网膜点图纪录.青光眼组的平均偏差和图形平均标准偏差显著较低(P＜0.001,P＜0.01).PERGN95,PhNR,b波以及PhNR/b波的幅值显著较低(P＜0.001).眼压升高降低了PERG与PhNR的振幅.     

Vigabatrin and retinal changes

Purpose: Vigabatrin is an effective antiepileptic drug but visual field constriction (VFC) is found to be a severe side-effect. The aims have been to investigate whether visual field constriction (VFC) is related to changes in the electroretinography (ERG). Methods: Twenty patients with localisations related epilepsy of whom one half had received vigabatrin were subjected to examination without informing about the treatment given. The eye examination included Goldmann perimetry and ERG. Results: All the patients had normal visual acuity. A total of three patients (30%) in the vigabatrin group and none in the control group were found to have VFC. In the vigabatrin group ERG examination were normal in one case, in five cases there were changes scotopic, photopic and in the oscillatory potentials (OP), while the remaining four had changes in two of these parameters. OPs were abnormal in eight of 10 patients. Of the three patients with VFC all had changes in ERG. The four patients with the most severe abnormalities in ERG had received high daily doses of vigabatrin (4 – 6 mg) in a period. In the control group no abnormality was observed in five cases, and in the remaining five changes were present in one or two of the potentials. Conclusion: It is found that 30% of patients treated with vigabatrin, develop VFC, and none in the control group. Similarly more patients in the vigabatrin group had changes in the ERG as compared to the control group, and the number of abnormal potentials are significantly higher among patients with VFC compared to those without. But the finding of abnormal ERG results is not synonymous with VFC, and this is important to bear in mind when examining patients that cannot cooperate to a VF examination. An individual sensitivity to vigabatrin is supposed, but severe ERG changes occurred in all patients having had high daily doses slant4 g.     

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.