Loss in pattern-elicited electroretinograms in optic nerve dysfunction

Sensitivity and specificity of the uniform field electroretinogram in glaucoma detection in comparison to the pattern electroretinogram

PURPOSE

To determine the ability of the photopic negative response (PhNR) of the uniform field electroretinogram (UF-ERG) to identify early glaucomatous changes in comparison to the checkerboard and bar stimuli of the pattern electroretinogram (PERG).

METHODS

Forty-nine glaucoma patients were classified into two groups: glaucoma-suspect (23 eyes) and early to moderate glaucoma (30 eyes), based on their clinical examination and the results of standard automated perimetry. Thirty patients (30 eyes) with intraocular pressures (IOP) of 21 mmHg or less, with no history of reported high IOP, were included as controls. PERG and UF-ERG recordings were obtained on a Diagnosys D-341 Attaché-Envoy System. Visual field testing was done only for glaucoma-suspect and glaucoma patients.

RESULTS

All three tests (PERG bar stimulus, PERG checkerboard stimulus and PhNR) displayed significantly prolonged peak times for glaucoma and glaucoma-suspect patients, with delays ranging from 7.8 to 14.8%, depending on the test. The PERG bar stimulus also showed a significantly lower N95 amplitude for both glaucoma groups (with reductions of 26.0% and 33.0% for glaucoma-suspect and glaucoma groups, respectively). The PERG checkerboard N95 amplitude component had high sensitivity for detecting glaucoma patients but a low specificity (97% and 37%, respectively; AUC = 0.61). Overall, the PhNR peak time showed the highest sensitivity and specificity (77% and 90%, respectively; AUC = 0.87).

CONCLUSIONS

PERG bar stimuli and the PhNR of the UF-ERG can be used in the clinical setting to detect glaucoma-related changes in glaucoma-suspect and glaucoma patients. However, our data confirm that the PhNR peak time has the best combined sensitivity and specificity.

Comparison of structural and functional tests in primary open angle glaucoma

Purpose:

To comparatively analyze the structural and functional tests used in the diagnosis and follow-up of glaucoma.

Methods:

Eighty eyes of 40 patients with primary open angle glaucoma (POAG) and 46 eyes of 23 healthy individuals were included in the study. Transient pattern electroretinography (PERG), steady-state PERG (ssPERG), computerized visual field (VF) screening, and examination of retinal nerve fiber layer (RNFL) and macular thickness on optical coherence tomography (OCT) were undertaken. The results were compared between the groups.

Results:

80 eyes belonging to 40 patients with a diagnosis of POAG (23 female, 17 male) (18 mild 22 moderate POAG) with a mean of 57.37 (±8.6) years, and 46 eyes of 23 healthy individuals (14 female, 9 male) with a mean age of 55.30 (±8.09) years were included in the study. PERG P50 and N95 and ssPERG latency revealed a significant delay in the POAG group. When the wave amplitudes were examined, they were found to be significantly lower in both PERG and sSPERG tests for the POAG group, but the results were more pronounced in ssPERG. The latency values of PERG and ssPERG tests were not significantly correlated with any of the parameters of the remaining tests. However, the amplitude values of these tests had a positive correlation with the mean deviation value and negative correlation with the pattern standard deviation value of VF. All associated parameters were significant for the amplitude value of the ssPERG test.

Conclusion:

For the proper management of glaucoma, rather than approaching damage simply as the loss of retinal ganglion cells or the neuroretinal rim, it is necessary to focus on the ongoing anatomical and functional relationship and evaluate structural and functional tests together. In addition, ssPERG test, which is not widely adopted in routine practice, provides valuable information and is significantly correlated with OCT parameters.

Discovery and clinical translation of novel glaucoma biomarkers

Glaucoma and other optic neuropathies are characterized by progressive dysfunction and loss of retinal ganglion cells and their axons. Given the high prevalence of glaucoma-related blindness and the availability of treatment options, improving the diagnosis and precise monitoring of progression in these conditions is paramount. Here we review recent progress in the development of novel biomarkers for glaucoma in the context of disease pathophysiology and we propose future steps for the field, including integration of exploratory biomarker outcomes into prospective therapeutic trials. We anticipate that, when validated, some of the novel glaucoma biomarkers discussed here will prove useful for clinical diagnosis and prediction of progression, as well as monitoring of clinical responses to standard and investigational therapies.

[Pattern electroretinogram and macular perfusion in glaucoma]

PURPOSE

To study microcirculatory and functional changes in macula in patients with Primary Open-Angle Glaucoma (POAG).

MATERIAL AND METHODS

The study included 95 POAG patients and 42 healthy control subjects. Whole en face image vessel density (wiVDRetina) was measured both in fovea and in parafovea using OCT-angiography (OCT-A) by means of SD-OCT AngioVue on Avanti RtVue xR (Optovue Inc., U.S.A.). Macular thickness and parameters of macular ganglion cell complex (GCC) were measured on the same day. Blood flow in the retrobulbar vessels was evaluated by means of Color Doppler Imaging (CDI). Pattern electroretinogram (PERG) was also taken from the study eyes. Correlations between PERG, SD-OCT GCC, macular thickness, and the parameters of OCT-A and CDI were studied.

RESULTS

The amplitude of t-PERG P50 decreased from 6.1±1.3 µV in normal eyes to 2.8±1.6 µV (p<0.0001) in early glaucoma and to 2.3±1.5 µV (p=0.93) in advanced stages. Relative vessel density of the capillary bed decreased from 51.3±3.0% in normal eyes to 45.9±5.0% (p<0.001) and to 41.8±5.0% (p=0.023) in early and advanced glaucoma respectively. The parameters of OCT-A and CDI correlated with morphological and functional parameters in normal and early glaucomatous eyes.

CONCLUSION

The study revealed reduction of macular microcirculation and decrease of PERG in early glaucoma. Correlations between the circulatory parameters and functional changes were found in early stages of the disease.

A comparative study of structural, functional and circulatory parameters in glaucoma diagnostics

PURPOSE

To compare the diagnostic accuracy of structural parameters, vessel density (VD) measured by optical coherence tomography angiography (OCTA), and electrophysiological testing in diagnosis of primary open-angle glaucoma (POAG).

METHODS

35 healthy participants and 90 POAG subjects underwent the measurement of whole image en face (wi) VD in the disc/peripapillary region and macula, the retinal nerve fiber layer (RNFL), and the average thickness of ganglion cell complex (GCC), pattern electroretinograms and pattern visual evoked potentials. The area under the receiver operating characteristic curve (AUC) was assessed for each parameter to differentiate early POAG from healthy eyes and between the POAG stages.

RESULTS

To distinguish early POAG from healthy eyes, the parameters with the highest AUC were detected: P50 amplitude of transient pattern electroretinogram, 1° (AUC 0.93, p = 0.002), P1 component of steady-state pattern electroretinogram (AUC 0.92, p = 0.003), P100 amplitude of pattern visual evoked potential, 1° (AUC 0.84, p = 0.013), wiVD macula superficial (AUC 0.80, p = 0.001), wiVD Disc (AUC 0.74, p = 0.016), GCC (AUC 0.74, p = 0.016) and to distinguish early POAG from the moderate to severe POAG: inferotemporal peripapillary VD (AUC 0.94, p < 0.0001) and focal loss volume of GCC (AUC 0.92, p < 0, 001).

CONCLUSIONS

Our results demonstrate the importance of measuring the microcirculation parameters in the macular area along with PERGs and PVEPs for the early detection of glaucoma. VD in the inferotemporal sector of the peripapillary retina and focal loss volume of the GCC are important for monitoring of the disease. The inclusion of OCTA, PERGs and PVEPs in glaucoma diagnostics may improve its early detection and monitoring.

Electropysiologic evaluation of the visual pathway in patients with multiple sclerosis

PURPOSE

To evaluate the ability of visual evoked potentials and pattern electroretinograms (PERG) to detect subclinical axonal damage in patients during the early diagnostic stage of multiple sclerosis (MS). The authors also compared the ability of optical coherence tomography (OCT), PERG, and visual evoked potentials to detect axonal loss in MS patients and correlated the functional and structural properties of the retinal nerve fiber layer.

METHODS

Two hundred twenty-eight eyes of 114 subjects (57 MS patients and 57 age- and sex-matched healthy controls) were included. The visual pathway was evaluated based on functional and structural assessments. All patients underwent a complete ophthalmic examination that included assessment of visual acuity, ocular motility, intraocular pressure, visual field, papillary morphology, OCT, visual evoked potentials, and PERG.

RESULTS

Visual evoked potentials (P100 latency and amplitude), PERG (N95 amplitude and N95/P50 ratio), and OCT parameters differed significantly between MS patients and healthy subjects. Moderate significant correlations were found between visual evoked potentials or PERG parameters and OCT measurements.

CONCLUSIONS

Axonal damage in ganglion cells of the visual pathway can be detected based on structural measures provided by OCT in MS patients and by the N95 component and N95/P50 index of PERG, thus providing good correlation between function and structure.

Frequency doubling technology, optical coherence technology and pattern electroretinogram in ocular hypertension

BACKGROUND

To assess which of three methods, namely, optical coherence tomography (OCT), pattern electroretinogram (PERG) or frequency-doubling technology (FDT), is the most sensitive and specific for detecting early glaucomatous damage in ocular hypertension (OH).

METHODS

Fifty-two patients with OH (24 men and 28 women, mean age of 56 ± 9.6 years) with an intraocular pressure (IOP) > 21 mm Hg and fifty-two control patients (25 men and 27 women, mean age of 54.8 ± 10.4 years) with IOP < 21 mm Hg, were assessed. All the patients had normal visual acuity, normal optic disk and normal perimetric indices.All subjects underwent OCT, FDT and PERG. Data were analyzed with unpaired t-tests, Chi-square test and Receiver Operating Characteristic (ROC) curve analyses.

RESULTS

In patients with OH, OCT showed retinal nerve fiber layer (RNFL) thinner than in control group in the superior quadrant (130.16 ± 10.02 vs 135.18 ± 9.27 μm, respectively; p < 0.011) and inferior quadrant (120.14 ± 11.0 vs 132.68 ± 8.03 μm; p < 0.001). FDT showed a significantly higher pattern standard deviation (PSD) (3.46  ± 1.48 vs 1.89 ± 0.7 dB; p < 0.001). With respect to PERG, only the amplitude showed significant differences (p < 0.044) between the two groups. ROC curve analysis revealed a sensitivity and specificity of 92% and 86%, respectively, for FDT-PSD (with an area under the ROC curve of 0.940), whereas with OCT, a sensitivity of 82% and a specificity of 74% was recorded in the inferior RNFL quadrant (with an area under the ROC curve of 0.806) finally with PERG amplitude we found a sensitivity of 52% and specificity of 77% (with an area under the ROC curve of 0.595).

CONCLUSIONS

FDT is the most sensitive and specific method for detecting early glaucomatous damage in eyes with OH, and together with OCT, can be useful in identifying those patients who may develop glaucoma.

TRIAL REGISTRATION

ISRCT number: ISRCTN70295497.

Diagnostic accuracy of pattern electroretinogram optimized for glaucoma detection

PURPOSE

To assess the ability of the new pattern electroretinogram optimized for glaucoma detection (PERGLA) paradigm to discriminate between healthy individuals and individuals with glaucomatous optic neuropathy (GON).

DESIGN

Cross-sectional study.

PARTICIPANTS

One hundred forty-two eyes of 71 participants (42 healthy and 29 with GON in at least 1 eye) enrolled in the University of California, San Diego, Diagnostic Innovations in Glaucoma Study were studied. Healthy individuals were those recruited as healthy with healthy-appearing optic disc by examination and masked stereoscopic optic disc photograph evaluation. Glaucomatous optic neuropathy was defined based on stereophotograph evaluation.

METHODS

The PERGLA (Glaid Elettronica, Pisa, Italy) recordings were obtained within 6 months of standard automated perimetry (SAP) testing. Dependent variables were PERGLA amplitude, phase, amplitude asymmetry, phase asymmetry, and SAP pattern standard deviation (PSD) and mean deviation (MD).

MAIN OUTCOME MEASURES

Diagnostic accuracy (sensitivity and specificity) of the PERGLA normative database for classifying healthy and glaucomatous individuals was determined. In addition, performance (areas under receiver operating characteristic curves [AUCs]) of PERGLA amplitude and phase for classifying healthy (n=84) and GON (n=50) eyes was determined. Results from both analyses were compared with those from SAP.

RESULTS

Sensitivity and specificity of the PERGLA normative database were 0.76 and 0.59, respectively, compared with 0.83 and 0.77 for SAP. The AUCs for PERGLA amplitude and phase were 0.75 and 0.50 (chance performance), respectively. The AUCs for SAP PSD and MD were 0.83 and 0.78, respectively.

CONCLUSIONS

Pattern electroretinograms recorded using the PERGLA paradigm can discriminate between healthy and glaucoma eyes, although this technique performed no better than SAP at this task. Low specificity of the PERGLA normative database suggests that the distribution of recordings included in the database is not ideal.

Update on the pattern electroretinogram in glaucoma

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Experimentally reduced perfusion of one eye impairs retinal function in both eyes

PURPOSE

The oscillatory potential index of scotopic white flash electroretinograms is reversibly enhanced in the contralateral eye when the ocular perfusion pressure (OPP) to the test eye is transiently reduced. A transient increase in the intraocular pressure (IOP) and decrease in the OPP in the test eye induced quantifiable vascular changes in the optic nerve head of the contralateral eye. We explored this contralateral phenomenon looking at ganglion cell function in both eyes during elevated IOP and decreased OPP in the test eye only. Our specific objective was to characterize the effects that transient hypoperfusion had on the neural generators of the pattern-reversal electroretinograms (pERGs), the ganglion cells, and preganglion neurons.

METHODS

A transient elevation in the IOP was sustained in 10 healthy subjects by scleral suction to reduce the baseline OPP by 15, 30, 45, and 60% for 2-min intervals. For each level of OPP, pERGs were evoked by a checkerboard with 75 minarc high-contrast black-white checks reversing at 5 Hz and recorded bilaterally using DTL fiber electrodes. The pERGs were also recorded immediately after removal of scleral suction and at 2-min intervals thereafter for an 8-min recovery interval.

RESULTS

The unilateral decrease in OPP differentially reduced the pERG in the test and contralateral eyes. The pERG for the test eye returned to baseline amplitude within 2 min of removing the suction cup. In contrast, the pERG in the contralateral eye remained below baseline throughout the entire 8-min recovery interval.

CONCLUSIONS

The observation of a bilateral decrease in the pERGs while the OPP was decreased in the test eye only suggested that these neuronal changes were modified at more central visual centers for retinal function to be compromised bilaterally. This latter effect may have been mediated by the transiently altered OPP or yet unknown neurohormonal mechanisms.

Spatial and temporal visual filtering in patients with glaucoma and ocular hypertension

PURPOSE

To investigate the spatial and temporal response characteristics in patients with glaucoma and ocular hypertension (OHT), in order to demonstrate the earliest specific measure of vision loss and to elucidate the precise mechanism of early glaucomatous damage.

METHODS

The Open Optical View System was used to assess changes in spatial and temporal vision in patients with clearly defined glaucoma (30 eyes), patients with OHT (30 eyes) and 30 eye-matched normal control eyes. The psychophysical methods applied were developed by Barber and Ruddock, who showed that the responses called ST1 and ST2 have similar characteristics to those found in the parvocellular and magnocellular pathway respectively. The measurement of spatial and temporal responses rests upon the measurement of a target that moves across a background, itself modulated spatially (gratings) and temporally (flicker).

RESULTS

The results reported, taken together with the current data on retinal ganglion cell function, reveal damage to both the parvocellular and magnocellular pathway in patients with glaucoma. In the OHT groups only marginal changes were found in the parvocellular response, but significant changes in the magnocellular response. In both OHT and glaucoma, the temporal processing shows greatest abnormalities at a small number of low flicker frequencies.

CONCLUSION

We provide psychophysical evidence of the detectable ganglion cell damage in patients with OHT who remain normal on testing with automated perimetry. The psychophysical method chosen (which measures the function of specific sub-divisions of the visual pathway) may prove useful in screening for glaucomatous damage.

Electrophysiology and psychophysics in ocular hypertension and glaucoma: evidence for different pathomechanisms in early glaucoma

It is not clear whether glaucomatous optic nerve damage is the end result of one pathological process or whether there are several mechanisms by which the final disease is manifest. The use of electrophysiological and psychophysical tests which measure the function of specific subdivisions of the visual pathways have been shown to be of use in the early diagnosis of glaucoma. In addition these results may help to elucidate the mechanisms of loss of visual function in patients with early glaucoma. One hundred and ninety-three patients with ocular hypertension (intraocular pressure > 24 mmHg, with normal visual fields and optic discs), 30 with glaucoma and 35 controls underwent pattern electroretinogram (PERG), peripheral colour contrast thresholds, motion detection thresholds (MDT) and Humphrey automated visual fields at the same visit. For each test there was a significant proportion of patients with abnormal results as has been found in previous studies of these techniques. However, there was a significant lack of correlation between the groups with only a small number of patients having abnormalities on more than one test. Of the patients demonstrating abnormal PERGs, 36% had abnormal colour contrast and 32% abnormal MDT, but only 15% were abnormal on both tests. Early glaucomatous damage may be focal or diffuse in nature. Similarly there may be preferential damage to ganglion cells subserving different visual functions or damage at different retinal layers. The results lend support to these hypotheses and give further evidence that more than one pathomechanism may be involved early in the glaucomatous process.

Pattern electroretinogram and automated perimetry in patients with glaucoma and ocular hypertension

To determine whether the pattern electroretinogram can improve the objectivity of visual field assessment, 39 patients with glaucoma and ocular hypertension were studied. This was to establish whether there is a correlation between the pattern electroretinogram and the global indices (mean deviation and corrected pattern standard deviation) provided by automated perimetry using the Humphrey visual field analyser. A significant correlation was found between the amplitude of the P50 + N95 wave of the pattern electroretinogram and the mean deviation and corrected pattern standard deviation components of the visual field. The larger the deviation from normal of these indices, particularly the corrected pattern standard deviation, the smaller the amplitude of the pattern electroretinogram. This correlation between the pattern electroretinogram and visual field indices provides an additional measure of confidence when interpreting equivocal results of automated perimetry.

A novel noninvasive videographic method for quantifying changes in the chromaticity of the optic nerve head with changes in the intraocular pressure, pulsatile choroidal blood flow and visual neural function in humans

Vision loss in glaucoma may be due to the compressive effects of the intraocular pressure (IOP) on the ganglion cell axons, impaired blood flow to the optic nerve, or some combination of these two factors. While reducing the IOP may preserve vision in patients with elevated IOP, not all patients experience longterm benefits from this therapeutic approach. The survival of ganglion cells may be more dependent upon the degree of vascular perfusion of the optic nerve head (ONH). In this report we present some preliminary data on a new noninvasive videographic technique for elaborating the capacity of the ONH vasculature to maintain perfusion constancy in the presence of transient elevations of the IOP and reductions of the ocular perfusion pressure (OPP). Shortterm, stepwise reductions of the OPP in the test eye of visually normal subjects (n = 5) systematically altered both the chromaticity (hue, saturation, brightness) of the ONH and the pulsatile ocular blood flow (POBF) in the choroid. Similar transient reductions in the OPP were seen to impair normal retinal physiology, as indicated by a significant attenuation of the bilateral pattern-reversal electroretinograms (pERGs) in visually normal subjects (n = 7). This technique was also used to reveal spontaneous rhythmical variations in the ONH chromaticity which were linked to the cardiac pulse rate. This so-called "chromatic pulse" of the ONH offers potential as a useful clinical index for evaluating the vascular perfusion of the ONH. The diagnostic and prognostic potential of dynamic digital imaging for the detection of abnormal hemodynamics in the ONH is discussed.

PERG and spectral sensitivity in ocular hypertensive and chronic open-angle glaucoma patients

Pattern electroretrinography (PERG) was performed in 33 patients with chronic open-angle glaucoma (COAG), 18 ocular hypertensive (OH) patients, and 24 normal subjects. COAG patients exhibited significantly lower PERG amplitudes than did normal subjects (P8rps = 0.025; P16rps less than 0.0001). The OH patients fell into two distinct groups: those with normal PERG scores and those with lower than normal scores. OH patients with PERG scores significantly lower than control values demonstrated significantly larger cup-to-disc ratios (P = 0.002) and higher initial intraocular pressures (IOPs) than did OH patients with normal PERG scores (P = 0.021). In the 11 OH patients in whom spectral sensitivity measurement was available, statistically significant correlations were found between the blue-cone sensitivity loss and the PERG amplitude (r8rps = 0.772, P8rps = 0.0053 and r16rps = 0.699, P16rps = 0.0167, respectively. Our results demonstrate reduced PERG amplitude in high-risk OH patients and further illustrate the correlation between PERG amplitude and blue-cone spectral sensitivity in OH subjects. Confirmation of the roles of PERG and spectral sensitivity in the detection of early glaucoma requires longitudinal study.

Spatial frequency-selective losses with pattern electroretinogram in type 1 (insulin-dependent) diabetic patients without retinopathy

Neurosensory abnormalities have been implicated in the first stages of diabetic retinopathy. The activity of retinal ganglion cells in 24 Type 1 (insulin-dependent) diabetic patients with short disease duration without retinopathy on fluorescein angiography was investigated by using a pattern electroretinogram in response to sinusoidal gratings of different spatial frequencies (0.6, 1.0, 1.4, 2.2 4.8 cycles/deg), counterphase modulated at 8 Hz. The pattern electroretinogram reflects, at least in part, the activity of subsets of generators (i.e. ganglion cells) which show spatial selectivity. Mean pattern electroretinogram amplitude was significantly reduced in patients at lower and intermediate, but not at higher spatial frequencies compared with 40 age-matched control subjects. At 1.4 cycles/deg the pattern electroretinogram amplitude was significantly correlated (r = 0.59) with age at onset (p = 0.002) and duration of disease (p = 0.002). Our results suggest that in Type 1 diabetic patients without retinopathy, there is an early sensory deficit of specific inner retina neurons which respond preferentially to gratings of medium and large size.

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.

Pattern electroretinogram peak times as a clinical means of discriminating retinal from optic nerve disease

Fifty-two patients with unilateral or bilateral retinal or optic nerve disease exhibited abnormal peak times and/or amplitudes in the pattern electroretinogram. While this abnormality in patients with optic nerve diseases was confined to an amplitude reduction, 40% of the eyes with retinal diseases exhibited additionally a peak time delay of the p and/or q component. We conclude that recording of pattern electroretinogram peak times provides an additional means to distinguish retinal from optic nerve diseases.

The pattern-evoked electroretinogram (PERG): age-related alterations and changes in glaucoma

Pattern-onset electroretinograms (PERGs) were studied in 147 normal subjects of different ages (14-79 years) and in 110 eyes of 65 patients with glaucoma or ocular hypertension. The responses showed an increase (P less than 0.001) in peak latency with increasing age and a decrease (P less than 0.001) in amplitude which approximately parallels the loss of ganglion cells estimated by other authors. Many glaucoma eyes showed a loss of the normally present spatial tuning. In the age group above 50 years 50% of the onset responses were significantly diminished and the peak latencies were not significantly different. A negative correlation (P less than 0.001) was found between the size of the PERG and the cup/disc ratio and a positive correlation (P less than 0.001) with the area of the neuroretinal rim of the optic disc. The PERG decreased (P less than 0.01) with increasing visual field losses.

The pattern electroretinogram in glaucoma: an evaluation by relative amplitude from the Bjerrum area

A new concept for evaluating the pattern electroretinogram (PERG) in glaucoma and its clinical application are described. The PERG was elicited by two different stimulus fields, namely, the whole central retinal area with a radius of 18 degrees and the paracentral ring area between the radius of 10 degrees and 18 degrees. The amplitude of the PERG for each stimulus field and the ratio of them were analysed for 30 patients with glaucoma or ocular hypertension. Among these only a small number of eyes were detected as abnormal when we evaluated the amplitude itself either with the central stimulus or the paracentral ring stimulus, whereas the ratio of the two values was below normal in some cases of advanced glaucoma. We conclude that the ratio of the paracentral to central PERG is useful for detecting glaucoma.

The pattern electroretinogram and visual-evoked potential in glaucoma

The pattern electroretinogram (PERG) may reflect ganglion cell or inner retinal layer activity. The most sensitive spatial and temporal variables for testing patients with glaucoma have not yet been identified. Fifty-two glaucoma suspects, 51 glaucoma patients, and 28 normal subjects were studied with the PERG and VEP, using three repetition rates and three spatial frequencies. Fast Fourier transforms were calculated at each spatial frequency and reversal rate. An analysis of variance revealed that normals could be differentiated from ocular hypertension and glaucoma patients using the amplitude of the PERG (second and fourth harmonic). Abnormalities in phase of the PERG between groups were also detected. A discriminant analysis of all amplitude and phase data revealed that the phase shift of the response of the second harmonic at 11 alternations/s (15-min checks) and at 5.5 alternations/s (15-min checks) correctly identified 81% of the normal and 75% of the glaucoma patients. The phase shift determinations of the VEP revealed significant abnormalities using 2 and 1/2 standard deviation confidence limits. There was significant overlap in the pattern ERG amplitude and phase shift in all three groups.

Pattern electroretinograms in ocular hypertension

The authors recorded pattern electroretinograms at different spatial frequencies in 16 patients affected with ocular hypertension. In 12 of these subjects the electroretinograms dropped in amplitude around 2 cycles/degree. The authors attributed this finding to ocular hypertension, hypothesizing ischemic damage at the head of the optic nerve with consequent fiber atrophy and degeneration of ganglion cells.

Electrophysiological discrimination between retinal and optic nerve disorders

In this study we show how the Pattern ERG (PERG) can be used to distinguish between optic nerve and retinal disease. Records from eyes with RBN and delayed visual evoked responses are compared with those recorded from the normal fellow eyes. In optic nerve disease there is a selective reduction of the later negative component of the PERG. PERGs were also recorded from patients with mild diabetic retinopathy. These were divided into three groups on the basis of the delay in their Visual Evoked Potential (VEP). The amplitude of both positive and negative components of the PERG fall with increasing severity of the disease thus showing that the abnormally long delay in VEP found in some cases is due to retinal disease rather than optic nerve disease.

Pattern reversal electroretinogram (PRERG) abnormalities in ocular hypertension: correlation with glaucoma risk factors

The indices employed commonly for the diagnosis of glaucoma (tonometry, ophthalmoscopy and perimetry) do not always identify which patients with ocular hypertension (OHT) will develop primary open-angle glaucoma (POAG) before irreversible visual field loss is manifest (1). The human pattern reversal electroretinogram (PRERG) is a bioelectric response reflecting neural activity of the proximal retina. PRERG amplitude reductions have been observed in POAG and other diseases affecting the optic nerve and retinal ganglion cells. This study was designed to determine whether OHT patients exhibit PRERG amplitude reductions and whether PRERG results are correlated with routinely evaluated clinical parameters. Steady-state PRERG (16 rps) were elicited by high contrast (76%), phase alternating checkerboard patterns (15-20 min checks) from one eye of 130 patients with ocular hypertension and 47 age matched visual normals (AMVNs). A significant (p less than 0.05) reduction in PRERG amplitude was noted for the OHT patients and 11.5% of those patients exhibited PRERG amplitudes more than 2.0 standard deviations below the AMVN mean. PRERG amplitude was found to be positively correlated with diastolic blood pressure (DBP) and negatively correlated with age, but no correlation between PRERG amplitude and either IOP, C/D ratio, or systolic blood pressure was evident. The lack of correlation between PRERG amplitude and the commonly used clinical indices may suggest a complementary role for this neurophysiologic test in determining which OHT patients will develop glaucoma.

Signs of early damage in glaucomatous monkey eyes: low spatial frequency losses in the pattern ERG and VEP

Experimental glaucoma was created in one eye of three cynomolgus monkeys by argon laser application to the mid-trabecular meshwork. Simultaneous pattern electroretinograms (PERG) and pattern visual evoked potentials (PVEP) were measured in both control and glaucoma eyes to spatial frequencies of 0.5, 1.25, 2.5, and 3.5 cpd which were counterphase modulated at 6 Hz. The transient flash electroretinogram was also measured. While normal flash electroretinograms were recorded in all eyes both before and after the unilateral production of elevated intraocular pressure (IOP), reductions in PERG and PVEP amplitude were seen in the eyes with glaucoma as early as two weeks following a sustained increase of IOP, despite the absence of cupping of the optic nervehead judged by ophthalmoscopic examination and analysis of photograph by two observers. Optic nervehead abnormalities occurred subsequently. In glaucomatous monkey eyes, the earliest PERG and PVEP changes were most evident with lower spatial frequencies of stimulation. Our data suggest that the optimal stimulus parameters for the detection of early glaucoma are low spatial frequency patterns presented at a rapid rate of temporal modulation.

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.

Electrophysiological evidence that early glaucoma affects foveal vision

The pattern electroretinogram (PERG) and visual evoked potential (PVEP) were recorded simultaneously using a 1.1 cpd pattern which was counterphase modulated at 1 Hz. The responses of ocular hypertensive (OHT) eyes (with normal visual fields) and eyes with early glaucoma (with early visual field defects and/or early cupping of the optic nervehead) were compared to age-matched normal observers. All patients (26 eyes) and normal observers (14 eyes) had normal transient flash electroretinograms. Delays were seen in mean PERG latency in both OHT and early glaucoma eyes, while mean PERG amplitude was significantly reduced only in the early glaucoma eyes. The PVEP responses were 'unmeasurable' in 11/26 patient eyes because the waveforms were grossly abnormal in shape, making it impossible to identify the N- and P-components. The data were categorized in this manner: a patient response was considered abnormal if latency or amplitude exceeded normal limits (PERG or PVEP) or if the waveform was 'unmeasurable' due to its shape (PVEP only). Of the 26 patient eyes, we found that 8 eyes had normal PERG and PVEP, 11 eyes had abnormal PERG and PVEP, one eye had an abnormal PERG and a normal PVEP, and 6 eyes (3 patients) had a normal PERG and an abnormal PVEP. These data support the proposition that foveal vision (as assessed by the PVEP) may be affected by early glaucomatous damage. The relationship between the PERG and PVEP also was evaluated using a new measurement which we call the 'latency window'. Using this measurement, 15/26 patient eyes were abnormal-9 of these had 'unmeasurable' PVEPs. This measurement could be useful in classifying 'W'-shaped PVEPs as normal or abnormal.

Pattern electroretinogram and optic nerve section in pigeons

We studied the effect of optic nerve section on the pattern electroretinogram (PERG) of 10 pigeons. Base line PERG and flash ERG were measured prior to surgery and then one optic nerve was cut. We measured PERG at various time intervals up to 24 weeks after the section. There was a sharp drop in PERG amplitude immediately following the section. It gradually returned to normal levels in the following 24 weeks. Significant decreases in time to peak were noted at 1 and 16 weeks for 0.5 cycle per degree checks and at 1, 2 and 9 weeks for 0.25 cycle per degree checks. The ERG generated by a TV stimulus did not change in amplitude but had a shorter time to peak at 24 weeks for a high intensity stimulus and at 16, 18, 24 weeks for a low intensity stimulus. Light and electron microscopic sections (at 24 weeks) revealed an almost complete loss of nerve fibers in the optic nerve. Retinal sections revealed only a few surviving ganglion cells and a few nerve fibers. This suggests that in pigeons, PERG is not generated by ganglion cells.

The electrical response of the human eye to patterned stimuli: clinical observations

Following the first recording of electroretinographic responses in man to a barred pattern by Riggs and associates (1964) in normal and by Lawwill (1973, 1974) in clinical cases, the first striking observation of a complete loss of pattern electroretinogram (PERG) after injurious section of the optic nerve by Groneberg & Teping (1980) has led to the conclusion that the PERG originates from proximal retinal structures different from those responsible for the luminance electroretinogram (LERG). Typical changes of the PERG are seen during branch occlusion of the central retinal artery and vein. In ocular hypertension without visual field loss and glaucoma-related papillary changes the PERG is decreased at intraocular pressures above 26 mm Hg. In cases of primary glaucoma with regulated intraocular tension and without using miotics the amplitude of the PERG reflects the damage to the inner retinal layers. This favorably compares with the P100 latencies of the visual evoked cortical potential (VECP) which in primary glaucoma were partly within, partly outside the normal range. Other retinal diseases showing amplitude changes in the PERG are primary macular dystrophy, diabetic retinopathy, and the acute stage of optic neuritis. In all these cases the Ganzfeld LERG may be normal or nearly normal, whereas the PERG undergoes typical changes. On the contrary a highly preserved PERG can be recorded in cases of retinitis pigmentosa where the electrooculogram light rise and the LERG are already missing. In light of these findings the recording of PERG constitutes a new promising method of clinical electroretinography reflecting the activity of the hitherto omitted innermost retinal layers. It thereby contributes essentially to the location of disturbances within the visual system.

Significance of abnormal pattern electroretinography in anterior visual pathway dysfunction

The pattern electroretinogram (PERG) findings in 72 patients with disease of the anterior visual pathways are presented in relation to the site of dysfunction. Two components of the PERG are described which are selectively involved in different pathologies. In particular, the main positive P50 component is invariably affected in retinal/macular dysfunction, whereas the late negative N95 component is principally affected in optic nerve disease.

Pattern reversal retinal potentials in ocular hypertensives at high and low risk of developing glaucoma

The human pattern-reversal retinal potential (PRRP) is a bioelectrical response which reflects neural activity generated in the proximal retina. Visual diseases which affect the retinal ganglion cells and the optic nerve often produce significant reductions in the amplitude of the PRRP. PRRP amplitude reductions are frequently observed in patients with primary open-angle glaucoma. This investigation was designed to determine whether patients with ocular hypertension who are at risk of developing glaucoma also exhibit PRRP amplitude reductions. The results indicate that PRRP amplitude reductions do occur in some ocular hypertensives, but many other ocular hypertensives do not exhibit PRRP abnormalities.

Electrophysiological assessment of aphakic cystoid macular oedema

Focal electroretinograms (FERG), pattern electroretinograms (PERG), and visual evoked potentials (VEP) were studied in a group of 30 aphakic patients with cystoid macular oedema (ACME). When compared with a control group of age-matched aphakics, 35% of patients were found to have abnormal FERG responses and 53%--over half of whom had normal FERG responses--showed abnormal PERG amplitudes. Although most of the patients had associated optic disc leakage, VEP latencies were normal in 26 out of 30. These results may explain the more severe visual loss seen in some ACME patients where the ophthalmologically visible retinal changes do not seem sufficient to explain such reduction in vision.

The pattern electroretinogram in patients with optic nerve disease

We analyzed the electroretinogram elicited by pattern stimuli (PERG) in 29 patients with unilateral optic nerve disease. The normal fellow eyes served as a control. When the normal fellow eye was covered and the patient was asked to watch the center of the pattern stimuli with the affected eye, the poor fixation often caused irregular eye movements which resulted in a poor reproducibility of the response. In such instance we opened the normal fellow eye for fixation, which helped to stabilize the affected eye being examined even when visual acuity was extremely poor. The cross-talk phenomenon of the ERG and the reflection of the VER from the normal fellow eye were proved negligible in this recording condition. We analyzed PERGs in comparison with the visual acuity and the degree of optic atrophy. Unlike the results of many previous authors, little correlation was observed between PERG and these two factors. Most patient showed normal or only slightly abnormal PERG, even when the visual acuity was extremely poor and the optic disc was completely atrophic. Our results suggest that, at least with our method, PERG has extremely limited value in detection of optic nerve disease.

Pattern ERG and glaucomatous visual field defects

In the past five years numerous reports have suggested that ganglion cell function can be tested by means of a specialized form of electroretinography, the so-called pattern electroretinogram (PERG). Because of the important potentials of a ganglion cell test for clinical use this technique has been applied by several investigators to patients with (presumed) ganglion cell dysfunction, especially glaucoma. On grounds of principle we had reason to question whether the reported positive results should be attributed to ganglion cell dysfunction or to other factors such as optical disturbances. We investigated in this study the PERG as a function of visual field loss in glaucoma patients with careful control of optical factors. We did not find changes in PERG as a function of field loss. So either field loss is not related to the mass behaviour of ganglion cells, or ganglion cells are not the prime basis of the PERG. We believe the latter to be true.

The use of a system analysis approach to electrodiagnostic (ERG and VEP) assessment

To evaluate the integrity of a biological system and its constituent functional units, a systematic study of input-output relations adopted from engineering has proven appropriate. With such an approach, sequential analysis can be implemented to probe the various parameter extractions along, for example, the visual system. The a priori assumption in this approach is that the visual world is processed along functionally separate pathways yielding distinct percepts such as contrast and motion. This so-called channel approach has proven useful not only to basic vision research but also for clinical application. The present overview shows that on the basis of the ERG or VEP, a type of functional anatomy can be performed with the biological system of interest remaining intact. Finally, it will be demonstrated that electrophysiological output parameters of the visual system can also serve as a non-invasive entry to investigate general systemic disorders.

Pattern-reversal electroretinograms in ocular hypertension

Pattern-reversal electroretinograms (ERGs) were recorded from seven patients, aged 50 to 69 years, with clinical diagnosis of unilateral ocular hypertension. In four of the seven patients the pattern ERG amplitude from the hypertensive eye was reduced below the normal level of variability, when compared with the amplitude from the opposite normotensive eye (ratio less than 0.8). In three of these four cases excavation of the optic disk in the hypertensive eye was observed 6 to 15 months after the recording of reduced pattern ERG. The finding suggests that pattern ERG may be an useful objective method for early detection of functional damage in eyes with increased intraocular pressure.

Clinical study of the pattern electroretinogram in patients with optic nerve damage

We have recorded both pattern and flash electroretinograms (ERG) in two patients with unilateral optic nerve damage due to optic canal fracture over one year. The pattern ERG from the affected eye was reduced in amplitude by approximately 40% in one patient, 60% in the other, compared with that from their other, normal eyes, while the flash ERG was normal in all eyes. Reduced pattern ERG responses may depend on retrograde degeneration following damage to the optic nerve. The pattern ERG, however, was not totally lost in the eyes with marked optic atrophy. There is a possibility that the pattern ERG contains both contrast and luminance components in various proportions.

The luminance origin of the pattern electroretinogram in man

Electroretinograms (e.r.g.s) and visually evoked potentials (v.e.p.s) to pattern stimuli were recorded simultaneously from healthy subjects. The stimuli were produced by a configuration in which the luminance of two sets of spatial elements (checks) could be modulated independently. Experiments were designed to distinguish between contrast responses and non-linear luminance responses. In the first of two basic experiments, the luminance of only one set of checks was modulated, at a constant level in every trial. The other set was not modulated, but its luminance was set at various levels. Under these conditions the local luminance stimulation was kept equal for every trial whereas the contrast stimulation varied. Therefore, local luminance responses in these experiments were expected to be constant and contrast responses were expected to vary. The e.r.g.s were identical for all luminance settings of the unmodulated checks, suggesting that luminance rather than contrast determines the response. The v.e.p.s showed, on the contrary, the behaviour expected for contrast responses. In the second basic experiment the local luminance stimulation was also kept constant, but the phase difference between the modulations of the two sets of checks was varied between 0 deg (pure luminance stimulation) and 180 deg (pattern reversal). In this type of experiment the second harmonic responses to local luminance modulation are expected to decrease to a minimum as phase difference goes from 0 to 90 deg and increase again as phase difference goes to 180 deg. Contrast responses are expected to increase monotonically from zero to maximal at phase difference shifts from 0 deg (no contrast stimulation) to 180 deg (contrast reversal). The e.r.g.s decreased to a minimum at 90 deg phase difference and increase again with phase difference going to 180 deg. At 0 and 180 deg the same value was recorded. Consequently, the e.r.g. behaviour suggests a luminance origin of the responses. The v.e.p.s monotonically increased as phase difference went from 0 to 180 deg, thus suggesting a contrast origin of the responses. Two additional control experiments were performed. The first experiment compared the responses to homogeneous field red/green exchange and pattern red/green exchange, with the luminances of the red and green sources matched by heterochromatic flicker photometry. The exchange of luminance-matched red and green checks (pattern reversal) did not produce different e.r.g. responses from those recorded in response to homogeneous field red/green exchange. The v.e.p. showed a significant increase for the pattern stimulus.(ABSTRACT TRUNCATED AT 400 WORDS)

Pattern electroretinogram: use of noncorneal skin electrodes

Pattern electroretinograms (ERGs) were recorded in three adults by a noncorneal electrode technique: silver-silver chloride skin electrodes attached to the inferior orbit of the left eye while the subject monocularly viewed a high contrast checker-board that reversed in contrast at a rate of 10 Hz. Recordings revealed pattern ERGs with an average amplitude of 1.5 microV. In addition, pattern ERGs were recorded as a function of spatial frequency and contrast of a square-wave grating. The results showed that an increase in spatial frequency or contrast yielded an increase in the amplitude of the pattern ERG. The results demonstrate that the pattern ERG can be recorded with a noncorneal electrode technique and that the noncorneal electrode technique is sensitive to changes in retinal function. Finally, it is demonstrated that the pattern ERG can transfer between the eyes such that the pattern ERG from a viewing eye can be recorded from an electrode placed below an occluded eye.

Pattern-reversal electroretinograms and visual evoked cortical potentials in multiple sclerosis

Pattern-reversal and flash electroretinograms (ERG) and visual evoked cortical potentials (VECP) were recorded from 15 patients with definite multiple sclerosis (MS). All patients had prolonged VECP latency, indicating demyelination of one or both optic nerves. The pattern-reversal ERG amplitude was reduced below the level of normal variation (mean -2 SD) in 11 of the 22 eyes with prolonged VECP latency and in one of the eight eyes with normal VECP latency. The mean pattern-reversal ERG amplitude from eyes with prolonged VECP latencies was significantly lower than the mean amplitude from the normal controls. No abnormalities were observed in the flash ERGs. Degeneration of retinal ganglion cell axons has been demonstrated in MS patients. The amplitude reduction in the pattern-reversal ERG, observed in some 50% of the eyes with prolonged VECP latencies, is supposed to reflect retinal ganglion cell dysfunction or degeneration secondary to demyelination of the optic nerve.

Oscillatory potentials, flash and pattern-reversal electroretinograms in amblyopia

Oscillatory potentials (OP), flash and pattern-reversal electroretinograms (ERG) were recorded in 8 adult patients with amblyopia (visual acuity 0.3 or less) and 10 age-matched normal controls. No significant differences were observed in OPs between amblyopic and opposite eyes and normal controls. The pattern-reversal ERGs were significantly reduced in all amblyopic eyes. No significant side difference was found in the flash ERGs. The observed amplitude reduction in the pattern-reversal ERG might reflect dysfunction of the retinal ganglion cells, which have been supposed to be the main source of this type of ERG. No electrophysiological evidence could be demonstrated for a disturbed retinal function prior to the ganglion cell level.

Nasopharyngeal recordings separate retinal from optic nerve potentials

Electrical potentials in response to single flashes and to pattern-reversal stimuli presented in Maxwellian view were recorded from several intranasal locations by withdrawing a nasopharyngeal electrode from the epipharynx through the nose in steps of 1 cm. From the anterior parts of the nose a waveform could be obtained resembling the corneal electroretinogram. In the epipharynx an ERG was recorded which was inverted in polarity. This reversal in polarity was explained by assuming an electrical dipole of the retina oriented parallel to the electrode path. When the electrode was below and behind the posterior pole of the eye ball a high-frequency activity of increased amplitude was observed the origin of which could not be explained by the retinal dipole. It is suggested that these increased oscillations originate from the optic nerve. Their behavior is explained by a hypothetical electrical dipole of the optic nerve oriented vertical to the electrode path.

The pattern electroretinogram in optic nerve demyelination

The pattern electroretinogram (PERG) is probably generated by the ganglion cell layer of the retina whose axons constitute the conductive fibres of the optic nerves. A study was undertaken of the PERG in a group of patients with clinically definite multiple sclerosis who had suffered optic nerve demyelination to assess the value of recording the PERG as a method for electrophysiological determination of optic nerve dysfunction. Pattern visual evoked potentials (PVEP) were simultaneously recorded, each eye being stimulated separately, and four different check sizes were used. Although individual patients showed PERG abnormalities the results as a group showed no significant difference from the normal population so far as latency or amplitude of the PERG was concerned. Thus we conclude that the PERG, while an interesting measurement, does not satisfactorily reflect optic nerve dysfunction. Further, our results indicate that it is not such a useful measure as the pattern visual evoked response for detecting optic nerve disease.

The pattern electroretinogram in optic nerve disease

Pattern evoked electroretinograms (PERG), diffuse flash electroretinograms (ERG) and visual evoked potentials were studied in patients with unilateral optic nerve disease. Patients with Snellen acuities of less than 6/30 did not have recordable PERGs in their affected eye, whereas their diffuse flash ERGs were normal. The VEPs were correspondingly reduced or absent when recorded from the poorer seeing eyes. A second group of patients with Snellen acuity between 6/6 and 6/30 in the involved eye showed reductions in the mean PERG amplitude of the affected as compared with the normal eyes. All affected eyes showed an abnormal contrast threshold measured with the PERG amplitude. Such results underscore the diagnostic value of the PERG in detecting even mildly affected cases of optic nerve disease.

Electroretinograms evoked in man by local uniform or patterned stimulation

1. We have recorded electroretinograms (e.r.g.s) in normal subjects. Television monitors were used as stimulators. The screens were surrounded by brightly lit white reflecting surfaces to ensure that the responses were developed by defined retinal areas.2. Various types of stimuli were employed. Either (i) a pattern of dark and bright squares was reversed, to evoke a pattern e.r.g. (p.e.r.g.), (ii) the luminance of the uniform screen was abruptly increased and decreased to evoke a focal on-off e.r.g. or (iii) a pattern was made to appear and disappear from a uniform background. In each of these cases, the sequence of changes of luminance at any one point could be made identical. The aim of the experiments was to determine whether the e.r.g. was modified by the spatial organization of the stimulus.3. In other experiments a colour monitor was used so that (i) a red-green flicker, (ii) red-green pattern reversal or (iii) the appearance of a red-green pattern from a yellow background could be used as a stimulus. The responses were caused by the changes in hue, since all the colours were equiluminant.4. With black and white patterns the p.e.r.g. peaks 5 msec later than the focal on-off e.r.g. The largest response is produced by squares of 0.5-1 degrees subtense.5. The ratio of the amplitudes of the p.e.r.g. to the focal on-off response is largest for stimuli confined to the macula and smallest for those projected onto peripheral retina.6. The amplitude of responses to chequerboard reversing patterns increases nearly linearly with contrast up to the maximum contrast available.7. When patterns appear or disappear from a uniform screen, and there is an associated change in the quantity of light entering the eye, recognizable b-waves occur when the average screen luminance increases, independently of whether pattern contrast increases (appearance) or decreases (disappearance).8. When a pattern appears or disappears with no change in luminance, e.r.g.s are evoked at both ;on' and ;off'. The disappearance of the dark parts of the pattern causes the largest logarithmic increase in local retinal illumination. For patterns of square size > 4 degrees the pattern disappearance response is larger than for pattern appearance. As the square size is reduced, the appearance response grows and the disappearance response decreases. The e.r.g.s evoked by the appropriate changes in luminance of a uniform screen are no longer the same as those caused by the appearance and disappearance of the pattern.9. The responses to change of hue are 70% as large as those produced by black and white patterns. The same ratio occurs for pattern and focal on-off e.r.g.s.10. When coloured patterns appear from and disappear to a uniform field, the e.r.g.s. evoked are very similar to those recorded when the appropriate changes of hue occur in a uniform field. This result is quite different to the findings for black and white patterns (see 8 above).11. The results suggest that it is the change in local adaptation caused by the black and white patterns which modifies the e.r.g. and not the presence of contrasting borders.

Pattern electroretinograms and visual-evoked potentials in glaucoma and multiple sclerosis

Steady-state visual-evoked potentials and electroretinograms were simultaneously recorded in four patients with glaucoma and in five patients with multiple sclerosis. The stimuli included a homogenous field and a 2.3 cycles per degree sinusoidal grating that were counter-phase modulated at the rate of 7.5 Hz. We used narrow bandwidth spectral analysis to measure the response amplitudes and signal-to-noise ratios. Transient pattern visual-evoked potentials (1 Hz) were also measured for latency in each eye. We found abnormal pattern electroretinograms, based on the absence of a significant second harmonic component, in three of the four glaucomatous eyes although the homogenous field electroretinograms were normal. In the patients with multiple sclerosis, the pattern electroretinograms were abnormal in two eyes, but the transient visual-evoked potential latency had the highest diagnostic yield (seven of ten eyes).

Comparison of the spatial response properties of the human retina and cortex as measured by simultaneously recorded pattern ERGs and VEPs

Electroretinograms and visual evoked potentials were simultaneously recorded from adult subjects using a checkerboard pattern stimulus reversing at 0.94, 3.75 and 7.5 Hz. Two contrast levels were used: 30 and 85%. The data obtained from the cortex (VEPs) show spatial tuning properties for all temporal frequencies at both contrast levels, with the peak of the amplitude-check size function occurring between 15 and 30 min. Tuning properties were found at the retina but only at the high contrast level and for the faster (3.75 and 7.5 Hz) temporal frequencies. The results demonstrate that spatial tuning is present in the human retina but not under as wide a range of conditions as found at the cortex.