Electrophysiological discrimination between retinal and optic nerve disorders

Analysis of the slope between P50 and N95 waves of the large field pattern electroretinogram as an additional indicator of ganglion cell dysfunction

AIM

Dysfunction of the retinal ganglion cells (RGC) can be detected by the pattern electroretinogram (PERG) as a reduction of the N95 amplitude, a decrease of the ratio between N95 and P50 amplitude and/or a shortening of P50 peak time. Additionally, the slope from the top of the P50 towards the N95 (P50-N95 slope) is less steep than in control subjects. The aim of the study was to quantitatively evaluate this slope in large field PERGs in controls and patients with RGC dysfunction due to optic neuropathy.

SUBJECTS AND METHODS

Large field (21.6°X27.8°) PERGs and optical coherence tomography (OCT) data from 30 eyes of the 30 patients with different types of clinically confirmed optic neuropathies, and with P50 amplitudes within normal limits and abnormal PERG N95 were retrospectively analysed and compared to 30 healthy eyes of 30 control subjects. The P50-N95 slope was analysed with a linear regression from 50 to 80 ms after the stimulus reversal.

RESULTS

The patients with optic neuropathy exhibited a significant reduction of the N95 amplitude (p < 0.001) and N95/P50 ratio (p < 0.001), the P50 peak time was mildly shorter (p = 0.03). The P50-N95 slope was significantly less steep in eyes with optic neuropathies (- 0.089 ± 0.029 vs. - 0.220 ± 0.041, p < 0.001). Thickness of temporal RNFL and the P50-N95 slope appeared to be the most sensitive and specific parameters for detecting RGC dysfunction (AUC = 1.0).

CONCLUSIONS

The slope between the P50 and N95 waves of a large field PERG is considerably less steep in patients with RGC dysfunction and could thus be an efficient biomarker, particularly in the diagnosis of early or borderline cases.

Clinical electrophysiology of the optic nerve and retinal ganglion cells

Clinical electrophysiological assessment of optic nerve and retinal ganglion cell function can be performed using the Pattern Electroretinogram (PERG), Visual Evoked Potential (VEP) and the Photopic Negative Response (PhNR) amongst other more specialised techniques. In this review, we describe these electrophysiological techniques and their application in diseases affecting the optic nerve and retinal ganglion cells with the exception of glaucoma. The disease groups discussed include hereditary, compressive, toxic/nutritional, traumatic, vascular, inflammatory and intracranial causes for optic nerve or retinal ganglion cell dysfunction. The benefits of objective, electrophysiological measurement of the retinal ganglion cells and optic nerve are discussed, as are their applications in clinical diagnosis of disease, determining prognosis, monitoring progression and response to novel therapies.

Visual Disfunction due to the Selective Effect of Glutamate Agonists on Retinal Cells

One of the causes of nervous system degeneration is an excess of glutamate released upon several diseases. Glutamate analogs, like N-methyl-DL-aspartate (NMDA) and kainic acid (KA), have been shown to induce experimental retinal neurotoxicity. Previous results have shown that NMDA/KA neurotoxicity induces significant changes in the full field electroretinogram response, a thinning on the inner retinal layers, and retinal ganglion cell death. However, not all types of retinal neurons experience the same degree of injury in response to the excitotoxic stimulus. The goal of the present work is to address the effect of intraocular injection of different doses of NMDA/KA on the structure and function of several types of retinal cells and their functionality. To globally analyze the effect of glutamate receptor activation in the retina after the intraocular injection of excitotoxic agents, a combination of histological, electrophysiological, and functional tools has been employed to assess the changes in the retinal structure and function. Retinal excitotoxicity caused by the intraocular injection of a mixture of NMDA/KA causes a harmful effect characterized by a great loss of bipolar, amacrine, and retinal ganglion cells, as well as the degeneration of the inner retina. This process leads to a loss of retinal cell functionality characterized by an impairment of light sensitivity and visual acuity, with a strong effect on the retinal OFF pathway. The structural and functional injury suffered by the retina suggests the importance of the glutamate receptors expressed by different types of retinal cells. The effect of glutamate agonists on the OFF pathway represents one of the main findings of the study, as the evaluation of the retinal lesions caused by excitotoxicity could be specifically explored using tests that evaluate the OFF pathway.

The pattern of retinal ganglion cell dysfunction in Leber hereditary optic neuropathy

Leber inherited optic neuropathy (LHON) is characterized by subacute bilateral loss of central vision due to dysfunction and loss of retinal ganglion cells (RGCs). Comprehensive visual electrophysiological investigations (including pattern reversal visual evoked potentials, pattern electroretinography and the photopic negative response) performed on 13 patients with acute and chronic LHON indicate early impairment of RGC cell body function and severe axonal dysfunction. Temporal, spatial and chromatic psychophysical tests performed on 7 patients with acute LHON and 4 patients with chronic LHON suggest severe involvement or loss of the midget, parasol and bistratified RGCs associated with all three principal visual pathways.

Morphological and electrophysiological outcome in prospective intravitreal bevacizumab treatment of macular edema secondary to central retinal vein occlusion

PURPOSE

To evaluate intravitreal bevacizumab (IVB) treatment in patients with central retinal vein occlusion (CRVO) by spectral domain optical coherence tomography (OCT) and electroretinography (ERG).

METHODS

Twenty-two CRVO patients were treated with IVB injections and followed for 1 year. Morphological effect of treatment was observed with fluorescent angiography and OCT. Functional effect was followed with best corrected visual acuity (BCVA) and ERG: combined rod-cone response of the standard full-field ERG (dark adapted 3.0 ERG), photopic negative response (PhNR), and pattern ERG (PERG).

RESULTS

Best corrected visual acuity (BCVA) improved by 18.2 letters after 6 months (p ≤ 0.001) and additional 4.7 letters by the 12th month (p ≤ 0.001). The central retinal thickness of 829.8 ± 256.7 μm decreased to 398.8 ± 230 μm (p ≤ 0.001) after 6 months and to 303.7 ± 128.9 μm during the following 6 months (p ≤ 0.001). The total macular volume (14.4 ± 4.2 mm(3)) decreased to 9.6 ± 3.2 mm(3) and 8.5 ± 2.0 mm(3) after 6 months and 1 year of treatment, respectively (p ≤ 0.001). Electrophysiological measures improved significantly after 6 months and 1 year of treatment: the a-wave implicit time of dark adapted 3.0 ERG from 25.6 ± 2.3 to 24.1 ± 2.1 and 24.1 ± 2.0 ms (p ≤ 0.01); the PhNR from -5.9 ± 6.6 to -9.4 ± 6.1 and -10.4 ± 4.6 µV (p ≤ 0.05); the PERG P50 amplitude from 0.2 ± 0.3 to 0.9 ± 0.6 and 1.1 ± 0.6 µV (p ≤ 0.001); and N95 amplitude from 0.4 ± 0.6 to 1.2 ± 0.9 and 1.6 ± 0.9 µV (p ≤ 0.001).

CONCLUSIONS

Intravitreal bevacizumab (IVB) treatment of macular edema due to CRVO improved standard morphological measures and the electrophysiological function of outer and inner retinal layers, which was most evident in central retina.

The value of two-field pattern electroretinogram in routine clinical electrophysiologic practice

PURPOSE

To investigate the clinical use of the large-field pattern electroretinogram (PERG) as an adjunct test to the International-standard PERG in an unselected sequential cohort of patients referred for routine electrophysiologic assessment.

METHODS

Pattern electroretinograms to both 15° × 11° (International Society for Clinical Electrophysiology of Vision Standard) and 30° × 22° (large field) checkerboard field sizes were recorded in 277 consecutive electrophysiology patients, aged 10-79 years. Most patients had additional tests including full-field electroretinogram, electrooculogram, multifocal electroretinograms, or cortical visual evoked potential. Patient data were compared with data from 27 control subjects.

RESULTS

Satisfactory 2-field PERG data were obtained in 91% (N = 253) of patients; data from 24 patients (9%) were excluded because of poor compliance (n = 17) or nystagmus (n = 7). Standard PERGs were consistent with macular dysfunction in 44% of cases; large-field PERG revealed macular dysfunction in an additional 8% of eyes and helped to distinguish between localized central, predominantly paracentral, and widespread macular dysfunction. The results were consistent with multifocal electroretinogram and/or imaging studies on the same patients. In some patients with optic nerve disease, the large-field PERG provided clearer evidence of normal macular function than the standard PERG.

CONCLUSION

Routine use of the large-field PERG is a valuable complement to standard-field PERG testing in the evaluation and management of patients with different forms of macular or generalized retinal dysfunction and can be useful in patients with optic nerve disease.

Electroretinogram findings in unilateral optic neuritis

To report the electrophysiological findings in patients with unilateral optic neuritis (ON), with particular reference to the electroretinogram (ERG). A retrospective analysis of full-field ERG, pattern ERG (PERG) and pattern visual evoked potential findings from 46 patients with clinical and electrophysiological findings in keeping with unilateral ON. ISCEV standard ERGs did not significantly differ between the optic neuritis and fellow eyes, nor between patients with and without MS. Differences were present in the N95 component of the PERG, which was significantly lower in the affected eye, and the pattern reversal visual evoked potential, which showed significantly longer peak time (latency) in the affected eye. In addition, there was a significant difference between patients with and without multiple sclerosis (MS). No significant inter-ocular asymmetry in ISCEV standard ERGs was present in these cases of unilateral optic neuritis, either as a clinically isolated syndrome or as part of multiple sclerosis. All ERGs recorded were normal.

Wolfram syndrome 1 (Wfs1) gene expression in the normal mouse visual system

Wolfram syndrome (OMIM 222300) is a neurodegenerative disorder defined by insulin-dependent diabetes mellitus and progressive optic atrophy. This syndrome has been attributed to mutations in the WFS1 gene, which codes for a putative multi-spanning membrane glycoprotein of the endoplasmic reticulum. The function of WFS1 (wolframin), the distribution of this protein in the mammalian visual system, and the pathogenesis of optic atrophy in Wolfram syndrome are unclear. In this study we made a detailed analysis of the distribution of Wfs1 mRNA and protein in the normal mouse visual system by using in situ hybridization and immunohistochemistry. The mRNA and protein were observed in the retina, optic nerve, and brain. In the retina, Wfs1 expression was strong in amacrine and Müller cells, and moderate in photoreceptors and horizontal cells. In addition, it was detectable in bipolar and retinal ganglion cells. Interestingly, moderate Wfs1 expression was seen in the optic nerve, particularly in astrocytes, while little Wfs1 was expressed in the optic chiasm or optic tract. In the brain, moderate Wfs1 expression was observed in the zonal, superficial gray, and intermediate gray layers of the superior colliculus, in the dorsomedial part of the suprachiasmatic nucleus, and in layer II of the primary and secondary visual cortices. Thus, Wfs1 mRNA and protein were widely distributed in the normal mouse visual system. This evidence may provide clues as to the physiological role of Wfs1 protein in the biology of vision, and help to explain the selective vulnerability of the optic nerve to WFS1 loss-of-function.

Visually evoked potentials after panretinal photocoagulation in omani patients with uncontrolled diabetes mellitus

Aim:

To report on the changes of latency and amplitudes of the pattern VEP in patients with uncontrolled diabetes mellitus II and I before and after panretinal laser treatment.

Design:

Single center hospital based comparative study.

Methods:

One hundred eyes of patients with proliferative diabetic vitreoretinopathy, and HbA1C ≥ 10 percent were subjected to Pattern Visually Evoked Potentials (Medtronic keyopint system, Nicolet) prior to and 4 weeks after PRP. Results were compared to age-matched non-diabetic controls. Chi-Square test, and paired ‘t’ test were used for statistical analysis.

Results:

Preoperative mean VEP amplitude was 8.35mV±3.71, and not significantly different to the control group (mean 10.51mV±3.34) (chi square test p=1). Mean preoperative P100 latency was 106.93±7.90ms and significantly different to the control group (103.21±7.65ms) (paired t-test p=0.001). After laser treatment, VEP amplitudes decreased in 48/100 eyes (mean total 5.11mV±2.4), and P100 latency increased in 75/100 eyes (mean total 110.47±7.35ms).

Conclusion:

In this study, PRP was followed by a significant decrease in VEP amplitudes in 48 percent and increase in latency in 75 percent of eyes.

A review of primary hereditary optic neuropathies

The primary inherited optic neuropathies are a heterogeneous group of disorders that result in loss of retinal ganglion cells, leading to the clinical appearance of optic atrophy. They affect between 1:10,000 to 1:50,000 people. The main clinical features are a reduction in visual acuity, colour vision abnormalities, centro-caecal visual field defects and pallor of the optic nerve head. Electrophysiological testing shows a normal flash electroretinogram, absent or delayed pattern visually evoked potentials suggestive of a conduction deficit and N95 waveform reduction on the pattern electroretinogram, consistent with a primary ganglion cell pathology. The primary inherited optic neuropathies may be sporadic or familial. The mode of inheritance may be autosomal dominant, autosomal recessive, X-linked recessive or mitochondrial. Within each of these groups, the phenotypic characteristics vary in such features as the mode and age of onset, the severity of the visual loss, the colour deficit and the overall prognosis. A number of different genes (most as yet unidentified) in both nuclear and mitochondrial genomes, underlie these disorders. The elucidation of the role of the encoded proteins will improve our understanding of basic mechanisms of ganglion cell development, physiology and metabolism and further our understanding of the pathophysiology of optic nerve disease. It will also improve diagnosis, counselling and management of patients, and eventually lead to the development of new therapeutic modalities.

Optic disc morphology of patients with OPA1 autosomal dominant optic atrophy

BACKGROUND/AIMS

Patients with autosomal dominant optic atrophy (ADOA) are genetically heterogeneous, but all have disc pallor. A degree of cupping in ADOA can make the distinction from normal tension glaucoma (NTG) clinically difficult. This study aimed to clarify the features of the optic nerve of patients with ADOA at the OPA1 locus.

METHODS

29 patients (58 eyes), from 12 families, were identified in a prospective observational study of patients with ADOA examined by a single observer between 1995 and 1998, in whom genetic analysis showed either evidence for linkage to chromosome 3q28 or mutations in the ADOA gene, OPA1. All of the patients had disc and fundal photographs available for retrospective analysis. Clinical data collected included disc appearance, intraocular pressure, Snellen visual acuity, Hardy-Rand-Rittler colour vision plates, and Humphrey 30-2 visual fields.

RESULTS

Mean age at time of examination was 37 years and mean visual acuity was 6/24. Disc morphology showed temporal disc pallor in 30 eyes (52%) and total disc pallor in 28 eyes (48%). At least one disc showed a cup to disc ratio of more than 0.5 in 18 patients (28 discs, 48%). The temporal neuroretinal rim always showed pallor and shallow shelving (or saucerisation) was seen in 46 eyes (79%). Only 12 discs (21%) had deep excavation and baring of blood vessels. All of the patients had normal intraocular pressure and no family history of glaucoma. There was a temporal grey, pigmentary crescent in 12 patients (18 eyes, 31%) and peripapillary atrophy in 20 patients (40 eyes, 69%), but disc margin haemorrhages were not seen. There was no maculopathy or retinopathy.

CONCLUSION

The optic disc morphology, described for the first time in this genetically homogeneous population of patients with OPA1 ADOA, shows a distinctive absence of a healthy neuroretinal rim and shallow saucerisation of the optic disc cup, with frequent peripapillary atrophy.

Pattern electroretinography (PERG) and an integrated approach to visual pathway diagnosis

The pattern electroretinogram (PERG) provides an objective measure of central retinal function, and has become an important element of the author's clinical visual electrophysiological practice. The PERG contains two main components, a positivity at approximately 50ms (P50) and a larger negativity at approximately 95ms (N95). The P50 component is affected by macular dysfunction with concomitant reduction in N95. The PERG therefore complements the Ganzfeld ERG in the assessment of patients with retinal disease. In contrast, the ganglion cell origins of the N95 component allow electrophysiological evaluation of ganglion cell function both in primary disease and in dysfunction secondary to optic nerve disease, where selective loss of N95 can be observed. Both macular dysfunction and optic nerve disease can give abnormalities in the visual evoked cortical potential (VEP), and the PERG thus facilitates more meaningful VEP interpretation. This review addresses the origins and recording of the PERG, and then draws on extensive clinical data from patients with genetically determined retinal and macular dystrophies, other retinal diseases and a variety of optic nerve disorders, to present an integrated approach to diagnosis.

Visual prognostic value of the pattern electroretinogram in chiasmal compression

BACKGROUND/AIMS

The visual loss associated with compression of the optic chiasm by pituitary tumours may be transient or permanent, possibly related to the extent of irreversible retrograde degeneration to the retinal ganglion cells. The pattern electroretinogram (PERG) N95 component is thought to rise in relation to retinal ganglion cell function and hence may be a potential prognostic indicator for visual function following decompressive surgery.

METHODS

The notes and electrodiagnostic records of 72 eyes from 36 patients with chiasmal compression were retrospectively analysed.

RESULTS

The postoperative change in visual field was found to be associated with the PERG N95:P50 ratio (p=0.01). Improvement in visual field was shown by a greater proportion of eyes with a normal N95:P50 ratio (65%) than with an abnormal ratio (27%). No change in visual field occurred in 26% of the eyes with a normal N95:P50 ratio compared with 67% of those with an abnormal ratio. Only 8% of eyes showed a worsening of visual field following surgery, in similar proportions for eyes with normal and abnormal N95:P50 ratios. There was no significant relationship with visual acuity.

CONCLUSION

The PERG is a useful visual prognostic indicator in the preoperative assessment of chiasmal compression.

Electrophysiological findings in dominant optic atrophy (DOA) linking to the OPA1 locus on chromosome 3q 28-qter

Pattern and flash visual evoked cortical potentials (PVEP, FVEP), and pattern electroretinograms, (PERG) were recorded in 13 affected individuals from 8 families with DOA. These were selected as representative from 87 affected members of 21 pedigrees with DOA who were examined, and who underwent genetic linkage analysis. Linkage to the OPA1 locus on chromosome 3q 28-qter was demonstrated in all families. VA ranged from 6/9 to HM: visual fields showed a variable centro-caecal defect; SLO (when performed) showed diffuse nerve fibre loss; MRI (when performed) showed small intra-orbital optic nerves. In 9/13 patients the PVEP was absent in one or both eyes. Most recordable PVEPs were of abnormal latency, but the delays were not marked (peak times 116-135 msec); amplitudes were low or subnormal. PERG fell within the normal range in 9 eyes of 7 patients. 14 eyes showed an abnormal N95:P50 ratio in keeping with ganglion cell dysfunction. Some severely affected eyes showed P50 component involvement, but in no eye was the PERG extinguished. Significant interocular asymmetries in at least one electrophysiological measure were present in 6/13 patients. Colour contrast thresholds were significantly elevated for all three colour confusion axes, with tritan being most affected.

Clinical features, molecular genetics, and pathophysiology of dominant optic atrophy

Inherited optic neuropathies are a significant cause of childhood and adult blindness and dominant optic atrophy (DOA) is the most common form of autosomally inherited (non-glaucomatous) optic neuropathy. Patients with DOA present with an insidious onset of bilateral visual loss and they characteristically have temporal optic nerve pallor, centrocaecal visual field scotoma, and a colour vision deficit, which is frequently blue-yellow. Evidence from histological and electrophysiological studies suggests that the pathology is confined to the retinal ganglion cell. A gene for dominant optic atrophy (OPA1) has been mapped to chromosome 3q28-qter, and studies are under way to refine the genetic interval in which the gene lies, to map the region physically, and hence to clone the gene. A second locus for dominant optic atrophy has recently been shown to map to chromosome 18q12.2-12.3 near the Kidd blood group locus. The cloning of genes for dominant optic atrophy will provide important insights into the pathophysiology of the retinal ganglion cell in health and disease. These insights may prove to be of great value in the understanding of other primary ganglion cell diseases, such as the mitochondrially inherited Leber's hereditary optic neuropathy and other diseases associated with ganglion cell loss, such as glaucoma.

The pattern electroretinogram in anterior visual pathway dysfunction and its relationship to the pattern visual evoked potential: a personal clinical review of 743 eyes

The pattern electroretinogram (PERG) has now been in routine clinical use for sufficiently long to allow a personal clinical review of its relationship to the cortically generated pattern visual evoked potential (PVEP). The PERG and PVEP findings are presented from 520 eyes with optic nerve demyelination (382 eyes), optic nerve compression (90 eyes) or heredofamilial optic atrophy (48 eyes), and these are compared with the findings obtained in 223 eyes with dysfunction anterior to the retinal ganglion cells. Dysfunction anterior to the retinal ganglion cells gives a reduction in the P50 component of the PERG, but this component is usually spared in optic nerve disease where selective loss of the N95 component is by far the most frequently occurring abnormality. A diagnostic strategy is presented.

Impaired VEP after photostress response in multiple sclerosis patients previously affected by optic neuritis

The aim of our work was to evaluate if an optic nerve involvement (multiple sclerosis patients previously affected by optic neuritis) may induce any change in visual evoked potential (VEP) after photostress response. VEP in basal conditions and after photostress were assessed in 10 patients with defined multiple sclerosis without a history of optic neuritis (MSWO); in 14 patients with defined multiple sclerosis previously affected by optic neuritis but with complete recovery of the visual acuity (MSON) and in 14 age-matched controls. In order to complete the investigation of the retinal function, Transient Pattern electroretinogram (PERG) and steady-state focal-ERG (counterphased gratings presented at 8 Hz in the macular region) were performed in MSON patients only. In MSWO eyes VEP parameters in basal condition and after photostress did not undergo significant changes compared to controls (ANOVA; P > 0.05). In MSON eyes we observed basal VEP with delayed P100 peak latency and reduced N75-P100 amplitude when compared with the control ones (P < 0.01). In MSON eyes the parameters of VEP after photostress underwent large changes and longer recovery time (RT) than in control and MSWO eyes (P < 0.01). In addition; in MSON eyes we found increased transient PERG P50 latency (P < 0.01) and reduced P50-N95 amplitude (P < 0.01); Focal-ERG (that displays a major component at 16 Hz; 2nd harmonic:2P) with reduced 2P amplitudes and delayed 2P phases (P < 0.01). Our results indicate that patients previously affected by optic neuritis present an abnormal VEP after photostress response and this may be ascribed predominantly to an involvement of the inner retinal layers as indicated by the concomitant impairment of PERG and focal-ERG responses.

Check size tuning of the pattern electroretingoram: a reappraisal

The pattern electroretinogram was recorded to checkerboard stimuli with a wide range of check sizes and two stimulus field sizes. Check sizes ranged from 0.25 degree to 7 degrees (field size, 16 degrees x 14 degrees) and 0.25 degree to 15 degrees (field size, 32 degrees x 27 degrees) in 14 and seven subjects, respectively. Reversal rate was 4.5/s. For minimal intrusion of blink artifacts the interrupted stimulation technique was employed. The P50 and N95 components of the pattern electroretinogram were evaluated separately. With both stimulus field sizes amplitude of P50 and N95 was maximal between 0.75 degree and 1 degree. With smaller check sizes the amplitude dropped monotonically. With larger check sizes field size played a role: with the 16 degrees x 14 degrees field, P50 gradually dropped to 89% from 1 degree to 7 degrees, which was paralleled by N95 only up to 7 degrees, where N95 dropped to 81% (p < 0.05). With the 32 degrees x 27 degrees field, there was no significant difference in size dependency between P50 and N95 for large check, both components staying constant from 1 degree to 15 degrees. We conclude that there is only minor large-check attenuation of the pattern electroretinogram, especially with a large field. The apparent field-size dependency may explain previous discrepancies in the literature.

Pattern electroretinogram, visual evoked potential and psychophysical functions in maculopathy

To compare pattern electroretinograms and visual evoked potentials with psychophysical examinations, such as visual acuity, static (automated) perimetry and color vision in unilateral maculopathies of various origins, 20 patients with unilateral retinal diseases within the macula and the posterior pole were tested. Pattern electroretinography, visual evoked potential testing and static perimetry (Octopus program M1) were performed with three different test field sizes (20 degrees x 20 degrees, 10 degrees x 10 degrees and 6 degrees x 6 degrees). The best correlation in all three test field sizes was found between visual acuity, static perimetry and visual evoked potential. This result is surprising, since central area defined functions (visual evoked potentials, visual acuity) correlated well with a total area integrating function (mean defect in static perimetry. The pattern electroretinogram, which seems to reflect an area-related function as well, showed a correlation to static perimetry only in the smaller 10 degrees x 10 degrees and 6 degrees x 6 degrees fields and not a significant correlation in the 20 degrees x 20 degrees field. Smaller stimulation fields may therefore produce sharper results in pattern electroretinographic testing. There was no correlation between pattern electroretinograms and visual evoked potentials or visual acuity. The pattern electroretinogram was recorded under monocular and binocular viewing conditions. In 60% of the patients, the amplitude of the affected eye was more reduced in the monocular than the binocular viewing condition; the healthy fellow eye controlled stable fixation of the affected eye more readily during binocular pattern electroretinogram registration. The degree of the color vision disturbance (C-index, desaturated panel D-15 test) did not correlate to any of the other examinations.

Vision

Images

The pattern electroretinogram: N95 amplitudes in normal subjects and optic neuritis patients

Recent work has suggested that the N95 peak of the transient pattern electroretinogram (PERG) may be a more sensitive indicator of the late stages of retinal function prior to optic nerve activation than the P50 peak. In this report, we show that a new measure of N95 amplitude, based on digital filtering methods to identify a non-linear baseline before measurement, greatly reduced the amplitude variation in a population of 50 normal subjects when compared with two other plausible measures. We then used that new measure to follow the time course of N95 amplitudes in 12 optic neuritis patients. It was found that maintenance of a normal N95 amplitude at 6 months after onset of optic neuritis was always associated with excellent clinical recovery as measured by visual fields, acuity, presence or absence of an afferent pupil and optic atrophy, and contrast sensitivity (CS). Loss of N95 amplitude to below laboratory limits of normal was associated with abnormalities in these indicators of visual function. This study supports the idea that the N95 peak represents retinal ganglion cell function.

Macular dysfunction in multiple sclerosis revealed by steady-state flicker and pattern ERGs

Recent evidence indicates that the 2nd harmonics of steady-state (8 Hz) electroretinograms to either sinusoidal flicker (FERG) or to counterphased gratings (PERG) presented in the macular region (9 degrees) represent different subsets of generators in the inner retina. We evaluated the steady-state macular FERG and PERG 2nd harmonics (2F and 2P, respectively) in 19 normal subjects (19 eyes) and in 23 multiple sclerosis patients (44 eyes; 25 eyes with a history of clinical optic neuritis, and 19 eyes with no history of optic neuritis, subclinical eyes). The mean 2F and 2P amplitudes were significantly reduced, as compared to controls, in both subclinical and optic neuritis eyes. The 2P phase was significantly delayed, as compared to controls, in subclinical eyes, whereas 2F phase was delayed in eyes with optic neuritis. 2F was outside the 95% confidence limits (in amplitude or phase) in 11/19 subclinical eyes and in 25/25 optic neuritis eyes. 2P was outside the normal range in 12/19 subclinical eyes and in 24/25 optic neuritis eyes. These results show that FERG and PERG 2nd harmonics are significantly altered in multiple sclerosis eyes with or without a clinical history of optic neuritis. This finding suggests a dysfunction of inner macular layers which may result from direct retinal involvement or retrograde degeneration.

The incidence of abnormal pattern electroretinography in optic nerve demyelination

This report describes the pattern electroretinogram (PERG) findings in 141 patients with optic nerve demyelination in one or both eyes. The overall incidence of PERG abnormality in the 199 eyes with abnormally delayed pattern visual evoked potential (PVEP) P100 component was 39.2%, with 84.6% of these PERG abnormalities being confined to the N95 component. The incidence of abnormal PERG was greater (53.3%) in those eyes with a history of retrobulbar neuritis than in those with sub-clinical demyelination (22.8%). The importance of stimulus parameters is noted. The value of the PERG in the improved interpretation of an abnormal PVEP is discussed.

Electrophysiology and colour perimetry in dominant infantile optic atrophy

A typical finding in dominant infantile optic atrophy (DIOA) is the variation of the phenotypic expression of the DIOA gene even within one family. It is of special interest for genetic consultation to evaluate an examination method for detecting subclinically involved patients. Seven patients of two families were examined. Three of them had the typical symptoms of DIOA: reduced visual acuity, tritan defect, temporal pallor of both optic discs, and a relative central scotoma for white test spots. In visual evoked cortical potentials (VECP) the amplitudes were reduced, and in one patient the latencies were slightly delayed and two patients considerably so. The amplitude of the negative component of the PERG was markedly reduced, while the positive component was normal. In the remaining four family members normal retinal and cortical responses were recorded under standard conditions and visual fields and colour vision (FM 100 hue) were also normal. However, static perimetry with blue test spots showed in two family members enlarged central scotomas, thus proving that they had subclinical DIOA.

Pattern electroretinograms in optic neuritis during the acute stage and after remission

A total of 20 patients with unilateral acute optic neuritis were studied. Each patient had experienced the recent onset of a decrease in visual acuity, a relative afferent pupillary defect, a relative or absolute central scotoma and a colour-vision defect. The pattern-reversal electroretinogram (PERG) of each patient was analysed with regard to the amplitude of the positive and negative components. During the acute stage the amplitude of the positive component was reduced in all patients and that of the negative, in 18 of 20 cases. Parallel to clinical recovery, a steady increase was observed in the amplitude of the positive component to normal values; no statistical differences between affected and fellow eyes was found. In contrast, the amplitude of the negative component remained significantly reduced after clinical recovery.

Pattern electroretinography in patients with delayed pattern visual evoked potentials due to distal anterior visual pathway dysfunction

Between March 1983 and January 1988 delayed pattern visual evoked potentials (PVEP) were observed in 67 patients with distal visual pathway dysfunction. Many of these patients had been referred for neurophysiological examination because of possible optic nerve dysfunction. These patients also had pattern electroretinography (PERG) performed which in all cases showed an abnormality of the main positive P50 component. None of these patients had an abnormality confined to the negative N95 component, the type of abnormality usually found if the PERG is abnormal in optic nerve disease. It is suggested that PERG recording should now be a routine adjunct to the PVEP in the assessment of anterior visual pathway dysfunction.

Coxsackie B5 papillitis

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Electroretinograms to checkerboard pattern reversal in cats: physiological characteristics and effect of retrograde degeneration of ganglion cells

Pattern electroretinograms (P-ERGs) evoked by alternating checks were studied in cats. Spatial frequency functions for transient and steady-state P-ERG waves showed a bimodal distribution with a preferred frequency at 0.6-0.75 c/deg and a second amplitude increase at frequencies lower than 0.5 c/deg. Decreasing the pattern luminance by 0.5 log units produced a shift of the spatial tuning curve toward lower spatial frequencies. No temporal tuning was noted in the temporal frequency functions. The bimodal distribution suggests that at spatial frequencies higher than 0.5 c/deg, the tuning reflects a 'contrast response' originating in cells with center surround organization. At spatial frequencies below 0.5 c/deg, the 'luminance response' becomes predominant and is generated in cells sensitive to mean luminance changes. Transient and steady-state P-ERGs to medium and high spatial frequencies were abolished by section of the optic nerve, while low spatial frequency stimuli at or below 0.3 c/deg continued to evoke P-ERGs at 1, 5 and 10 months after surgery. Quantitative whole mount retina microscopic examination confirmed the retrograde degeneration of the ganglion cells. It is concluded that both transient and steady-state P-ERGs to small and medium spatial frequencies checks are predominantly related to ganglion cell activity, while P-ERGs to low spatial frequencies reflect preganglionic cell activity.

Leber's hereditary optic atrophy

Leber described a particular type of hereditary optic atrophy in 1871. The clinical features of all cases since reported are reviewed. There is characteristically acute visual loss, circumpapillary teleangiectatic micropathy, tortuosity of the retinal vessels and oedema in the retinal nerve fibres. 85% of those affected are male, but affected fathers do not transmit the condition to their children. The exact mode of inheritance is still obscure but it is suggested that inheritance may be mitochondrial; enlarged subsarcolemmal mitochondria in LOA patients have been described. Colour vision defects are observed not only in patients, but also in presumed carriers. Electrophysiological investigations demonstrate optic nerve damage, but are not indicative of any particular pathology. It has been reported that in many cases of LOA the severity of the disease is related to tobacco smoking. Increased cyanocobalamin blood levels in patients and increased cyanide blood levels support this hypothesis.

Separable evoked retinal and cortical potentials from each major visual pathway: preliminary results

Single cell experiments in primates show that there are two major parallel pathways named after the lamination in the lateral geniculate nucleus. Each of these systems can be preferentially excited by appropriate stimuli. Here we report that in man the polarity of the evoked potentials both in retina and in cortex depends on which of these pathways is stimulated. The identification of the resulting waveforms is thereby simplified--a matter of practical importance. The fact that at retina and cortex there are characteristic potentials may reflect the different cell biology of the two pathways.

A review of the clinical applications of the pattern electroretinogram

The pattern electroretinogram (PERG) has recently been introduced as a clinical procedure. It has been thought by many to represent activity of the retinal ganglion cells, although this is still a matter of contention. The exciting prospect of a selective test of ganglion cell function led to the application of the PERG in a variety of ophthalmological conditions. In the course of these investigations the PERG was found to be diminished in cases of maculopathy, optic atrophy, optic neuritis, toxic optic neuropathy, neurotransmitter disorders, glaucoma and ocular hypertension and in retinal vascular disorders such as diabetes. It was also affected in some cases of amblyopia. This paper briefly describes the techniques used to record the PERG and reviews current literature pertaining to its clinical application.

The pattern electroretinogram

Physiological experiments and the exploitation of clinical conditions have provided compelling evidence that retinal ganglion cells and other inner retinal structures generate the pattern ERG (PERG). As an increasing number of clinical reports have been published some contradictory findings have been reported. These may be ascribed to variation in recording and measuring techniques. The PERG consists of two major portions, the early positive and the following negative component which can be investigated separately if the stimulus conditions allow isolated (or "transient") responses to be recorded. Care has to be taken in positioning the reference electrode, maintaining accurate refraction, and the influence of pupil size must be considered. Furthermore the PERG is contaminated by a luminance component which may be generated in the outer retina. The size of this increases with low spatial frequency (large check-sizes) and high mean luminance. The PERG permits the examination of an additional level of the retina and helps the understanding of pathophysiology of various eye diseases, and is of clinical importance in routine diagnosis and assessment. In glaucoma the PERG amplitude is often reduced before it is possible to detect a scotoma and it is therefore an important prognostic indicator in patients with ocular hypertension. In diabetic retinopathy, retinal ischaemia sufficient to lead to the pre-proliferative state can be demonstrated. The PERG also has a major clinical role in examining localised retinal pathology. If combined with VECP recording, it greatly extends the interpretations possible, since not only can damage to the optic nerve be detected by both tests, but the normal PERG in the presence of an abnormal PVECP implies that the losses are confined to the central pathway.