The multifocal pattern electroretinogram in glaucoma

The Use of the RETeval Portable Electroretinography Device for Low-Cost Screening: A Mini-Review

Electroretinography (ERG) provides crucial insights into retinal function and the integrity of the visual pathways. However, ERG assessments classically require a complicated technical background with costly equipment. In addition, the placement of corneal or conjunctival electrodes is not always tolerated by the patients, which restricts the measurement for pediatric evaluations. In this short review, we give an overview of the use of the RETeval portable ERG device (LKC Technologies, Inc., Gaithersburg, MD, USA), a modern portable ERG device that can facilitate screening for diseases involving the retina and the optic nerve. We also review its potential to provide ocular biomarkers in systemic pathologies, such as Alzheimer's disease and central nervous system alterations, within the framework of oculomics.

Novel Machine-Learning Based Framework Using Electroretinography Data for the Detection of Early-Stage Glaucoma

Purpose

Early-stage glaucoma diagnosis has been a challenging problem in ophthalmology. The current state-of-the-art glaucoma diagnosis techniques do not completely leverage the functional measures' such as electroretinogram's immense potential; instead, focus is on structural measures like optical coherence tomography. The current study aims to take a foundational step toward the development of a novel and reliable predictive framework for early detection of glaucoma using machine-learning-based algorithm capable of leveraging medically relevant information that ERG signals contain.

Methods

ERG signals from 60 eyes of DBA/2 mice were grouped for binary classification based on age. The signals were also grouped based on intraocular pressure (IOP) for multiclass classification. Statistical and wavelet-based features were engineered and extracted. Important predictors (ERG tests and features) were determined, and the performance of five machine learning-based methods were evaluated.

Results

Random forest (bagged trees) ensemble classifier provided the best performance in both binary and multiclass classification of ERG signals. An accuracy of 91.7 and 80% was achieved for binary and multiclass classification, respectively, suggesting that machine-learning-based models can detect subtle changes in ERG signals if trained using advanced features such as those based on wavelet analyses.

Conclusions

The present study describes a novel, machine-learning-based method to analyze ERG signals providing additional information that may be used to detect early-stage glaucoma. Based on promising performance metrics obtained using the proposed machine-learning-based framework leveraging an established ERG data set, we conclude that the novel framework allows for detection of functional deficits of early/various stages of glaucoma in mice.

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.

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.

The photopic negative response (PhNR): measurement approaches and utility in glaucoma

Purpose

Visual electrophysiological testing continues to generate interest among glaucoma experts because of its potential help in clarifying disease pathophysiology and promoting early detection of glaucomatous damage. The photopic negative response (PhNR) is a slow negative component of the full-field electroretinogram that has been shown to provide specific information about retinal ganglion cells (RGCs) activity. The purpose of this article is to review the literature to explore the currently available measurement methods and the utility of PhNR in glaucoma diagnostic process.

Methods

We gathered publications related to the origins, types of stimuli used, measurements methods and applications of the PhNR of ERG in animal models and humans through a search of the literature cited in PubMed. Search terms were: “PhNR”, “photopic negative response”, “glaucoma”, “glaucomatous optic neuropathy”, “ERG”, “electroretinogram”.

Results

The most reliable PhNR measurements are obtained using a red stimulus on a blue background, without requiring refractive correction, fixation monitoring, or ocular media transparency. Given its direct correlation with RGCs response, the PhNR measured as baseline-to-trough (BT) represents the most reliable parameter of evaluation. Glaucoma patients with evident perimetric defects show pathologic PhNR values. Even though the PhNR is promising in detecting early RGCs impairment, distinguishing between healthy subjects and suspect patients at risk of developing glaucomatous damage still remains challenging.

Conclusion

The PhNR is a useful additional tool to explore disorders that affect the innermost retina, including glaucoma and other forms of optic neuropathy. In particular, comparing reports of the standard examinations (optic disc assessment, OCT RNFL measurement, standard automated perimetry) with the results of electrophysiological tests may be helpful in solving clinical diagnostic and management dilemmas. On the one hand, the PhNR of the ERG can examine the parvocellular pathways; on the other hand, the steady-state pattern ERG optimized for glaucoma screening (PERGLA) can explore the magnocellular pathways. This could give ophthalmologists a useful feedback to identify early RGCs alterations suggestive of glaucoma, stratify the risk and potentially monitor disease progression.

Identification of clusters in multifocal electrophysiology recordings to maximize discriminant capacity (patients vs. control subjects)

PURPOSE

To propose a new method of identifying clusters in multifocal electrophysiology (multifocal electroretinogram: mfERG; multifocal visual-evoked potential: mfVEP) that conserve the maximum capacity to discriminate between patients and control subjects.

METHODS

The theoretical framework proposed creates arbitrary N-size clusters of sectors. The capacity to discriminate between patients and control subjects is assessed by analysing the area under the receiver operator characteristic curve (AUC). As proof of concept, the method is validated using mfERG recordings taken from both eyes of control subjects (n = 6) and from patients with multiple sclerosis (n = 15).

RESULTS

Considering the amplitude of wave P1 as the analysis parameter, the maximum value of AUC = 0.7042 is obtained with N = 9 sectors. Taking into account the AUC of the amplitudes and latencies of waves N1 and P1, the maximum value of the AUC = 0.6917 with N = 8 clustered sectors. The greatest discriminant capacity is obtained by analysing the latency of wave P1: AUC = 0.8854 with a cluster of N = 12 sectors.

CONCLUSION

This paper demonstrates the effectiveness of a method able to determine the arbitrary clustering of multifocal responses that possesses the greatest capacity to discriminate between control subjects and patients when applied to the visual field of mfERG or mfVEP recordings. The method may prove helpful in diagnosing any disease that is identifiable in patients' mfERG or mfVEP recordings and is extensible to other clinical tests, such as optical coherence tomography.

Macular and Multifocal PERG and FD-OCT in Preperimetric and Hemifield Loss Glaucoma

PURPOSE

To evaluate the ability of macular and multifocal (mf) pattern electroretinogram (PERG) to differentiate preperimetric glaucoma (PG) and glaucoma with hemifield loss (GHL) from controls, to compare the discrimination ability of PERG and fourier-domain optical coherence tomography (FD-OCT), and to assess the relationship between measurements.

PATIENTS AND METHODS

Standard automated perimetry, steady-state and transient PERG and mfPERG measurements were obtained from PG (n=14, 24 eyes), GHL (n=5, 7 eyes), and controls (n=19, 22 eyes). Circumpapillary retinal nerve fiber layer (cpRNFL), full-thickness macula, and segmented macular layer thicknesses on FD-OCT were investigated. Measurements were compared using mixed effects linear models. The relationships between measurements and the diagnostic performance of each technology were assessed.

RESULTS

Compared with controls, average P50 peak time transient PERG responses were reduced in PG and GHL, whereas average latency and amplitude steady-state and mfPERG responses were abnormal only in GHL. cpRNFL and macular thickness measurements in PG and GHL differed significantly from controls. A significant relationship was found between PERG and most FD-OCT or SAP parameters. Partial least squares discriminant analysis revealed that OCT parameters, along with mfPERG and transient PERG parameters had similar ability to discriminate PG and GHL from healthy controls.

CONCLUSIONS

PERG and OCT parameters may be abnormal, with significant correlations between measurements, in PG eyes. Both technologies may be useful for detection of early glaucoma.

Retinal conduction speed analysis reveals different origins of the P50 and N95 components of the (multifocal) pattern electroretinogram

The pattern electroretinogram (PERG), an indicator of retinal ganglion cell (RGC) function, comprises a P50 and an N95 component. We addressed the question of whether the N95 originates, like the P50, from the RGC bodies or from the change of axon orientation at the optic nerve head (ONH). Thus, we recorded multifocal PERGs for 36 retinal locations in 21 participants. Second-order kernel responses were analyzed for the dependence of peak time topography on retinal fiber lengths to the ONH separately for the positive and negative excursions. We found that peak times were longer for macular [P1 (P50-like): 50 ms; N2 (N95-like): 76)] than for peripheral responses [P1: 43; N2: 66]. For the N2 another factor was necessary to explain the variability: The time difference (deltaT: N2 minus P1) was found to be proportional to fiber length from ganglion cell body to the ONH. We calculated retinal fiber length using an analytical function by Jansonius et al. (2009, 2012) and found that a linear model with factors eccentricity and fiber length explained 82% of the total N2 time variance (p«0.001). The conduction speeds of the retinal axons were estimated from deltaT to range from 0.5 to 3.0 m/s for parafovea and periphery, respectively. The dependence of deltaT on the distance from ganglion cell body to the ONH suggests that the N2 originates at the ONH rather than at the ganglion cell body. While the multifocal N2 peaks earlier (≈76 ms) than the non-multifocal PERG-N95 (≈95 ms), considerations of high-pass filtering and frequency dependence of the mfPERG-N2 suggest that the source separation (P50 = ganglion cell body vs. N95 = ONH) also holds for the non-multifocal PERG.

Comparing three different modes of electroretinography in experimental glaucoma: diagnostic performance and correlation to structure

PURPOSE

To compare diagnostic performance and structure-function correlations of multifocal electroretinogram (mfERG), full-field flash ERG (ff-ERG) photopic negative response (PhNR) and transient pattern-reversal ERG (PERG) in a non-human primate (NHP) model of experimental glaucoma (EG).

METHODS

At baseline and after induction of chronic unilateral IOP elevation, 43 NHP had alternating weekly recordings of retinal nerve fiber layer thickness (RNFLT) by spectral domain OCT (Spectralis) and retinal function by mfERG (7F slow-sequence stimulus, VERIS), ff-ERG (red 0.42 log cd-s/m² flashes on blue 30 scotopic cd/m² background, LKC UTAS-E3000), and PERG (0.8° checks, 99% contrast, 100 cd/m² mean, 5 reversals/s, VERIS). All NHP were followed at least until HRT-confirmed optic nerve head posterior deformation, most to later stages. mfERG responses were filtered into low- and high-frequency components (LFC, HFC, >75 Hz). Peak-to-trough amplitudes of LFC features (N1, P1, N2) and HFC RMS amplitudes were measured and ratios calculated for HFC:P1 and N2:P1. ff-ERG parameters included A-wave (at 10 ms), B-wave (trough-to-peak) and PhNR (baseline-to-trough) amplitudes as well as PhNR:B-wave ratio. PERG parameters included P50 and N95 amplitudes as well as N95:P50 ratio and N95 slope. Diagnostic performance of retinal function parameters was compared using the area under the receiver operating characteristic curve (A-ROC) to discriminate between EG and control eyes. Correlations to RNFLT were compared using Steiger's test.

RESULTS

Study duration was 15 ± 8 months. At final follow-up, structural damage in EG eyes measured by RNFLT ranged from 9% above baseline (BL) to 58% below BL; 29/43 EG eyes (67%) and 0/43 of the fellow control eyes exhibited significant (>7%) loss of RNFLT from BL. Using raw parameter values, the largest A-ROC findings for mfERG were: HFC (0.82) and HFC:P1 (0.90); for ff-ERG: PhNR (0.90) and PhNR:B-wave (0.88) and for PERG: P50 (0.64) and N95 (0.61). A-ROC increased when data were expressed as % change from BL, but the pattern of results persisted. At 95% specificity, the diagnostic sensitivity of mfERG HFC:P1 ratio was best, followed by PhNR and PERG. The correlation to RNFLT was stronger for mfERG HFC (R = 0.65) than for PhNR (R = 0.59) or PERG N95 (R = 0.36), (p = 0.20, p = 0.0006, respectively). The PhNR flagged a few EG eyes at the final time point that had not been flagged by mfERG HFC or PERG.

CONCLUSIONS

Diagnostic performance and structure-function correlation were strongest for mfERG HFC as compared with ff-ERG PhNR or PERG in NHP EG.

Electroretinography in glaucoma diagnosis

PURPOSE OF REVIEW

Electrophysiological measures of vision function have for decades generated interest among glaucoma researchers and clinicians alike because of their potential to help elucidate pathophysiological processes and sequence of glaucomatous damage, as well as to offer a potential complementary metric of function that might be more sensitive than standard automated perimetry. The purpose of this article is to review the recent literature to provide an update on the role of the electroretinogram (ERG) in glaucoma diagnosis.

RECENT FINDINGS

The pattern reversal ERG (PERG) and the photopic negative response (PhNR) of the cone-driven full-field, focal or multifocal ERG provide objective measures of retinal ganglion cell function and are all sensitive to glaucomatous damage. Recent studies demonstrate that a reduced PERG amplitude is predictive of subsequent visual field conversion (from normal to glaucomatous) and an increased rate of progressive retinal nerve fiber layer thinning in suspect eyes, indicating a potential role for PERG in risk stratification. Converging evidence indicates that some portion of PERG and PhNR abnormality represents a reversible aspect of dysfunction in glaucoma.

SUMMARY

PERG and PhNR responses obtained from the central macula are capable of detecting early-stage, reversible glaucomatous dysfunction.

Electrophysiology and glaucoma: current status and future challenges

Visual electrophysiology allows non-invasive monitoring of the function of most processing stages along the visual pathway. Here, we consider which of the available methods provides the most information concerning glaucomatous optic nerve disease. The multifocal electroretinogram (ERG), although often employed, is less affected in glaucoma than two direct measurements of retinal ganglion cell function, namely the pattern ERG (PERG) and the photopic negative response (PhNR) of the ERG. For the PERG, longitudinal studies have been reported, suggesting that this method can be used for the early detection of glaucoma; for the PhNR, no longitudinal study is available as yet. The multifocal PERG can spatially resolve ganglion cell function but its glaucomatous reduction is typically panretinal, even with only local field changes and so, its topographic resolution is of no advantage in glaucoma. The multifocal visual evoked potential promises objective perimetry and shows sensitivity and specificity comparable with standard automated perimetry but has not been established as a routine tool to date.

Recent Advances towards the Clinical Application of Stem Cells for Retinal Regeneration

Retinal degenerative diseases constitute a major cause of irreversible blindness in the world. Stem cell-based therapies offer hope for these patients at risk of or suffering from blindness due to the deterioration of the neural retina. Various sources of stem cells are currently being investigated, ranging from human embryonic stem cells to adult-derived induced pluripotent stem cells as well as human Müller stem cells, with the first clinical trials to investigate the safety and tolerability of human embryonic stem cell-derived retinal pigment epithelium cells having recently commenced. This review aims to summarize the latest advances in the development of stem cell strategies for the replacement of retinal neurons and their supportive cells, the retinal pigment epithelium (RPE) affected by retinal degenerative conditions. Particular emphasis will be given to the advances in stem cell transplantation and the challenges associated with their translation into clinical practice.

Correlation between multifocal pattern electroretinography and Fourier-domain OCT in eyes with temporal hemianopia from chiasmal compression

PURPOSE

To evaluate the correlation between multifocal pattern electroretinography (mfPERG) and Fourier-domain optical coherence tomography (FD-OCT) with regard to macular and retinal nerve fiber layer (RNFL) thickness in eyes with temporal hemianopia from chiasmal compression.

METHODS

Twenty-five eyes from 25 patients with permanent temporal visual field defects from chiasmal compression and 25 healthy eyes were submitted to mfPERG using a stimulus pattern of 19 rectangles, standard automated perimetry and FD-OCT measurements. The mfPERG response was determined for groups of three rectangles for the nasal and temporal hemifields and for each quadrant. Macular thickness measurements were registered according to an overlaid OCT-generated checkerboard with 36 checks and averaged for the central area, and for each scanned quadrant and hemifield. RNFL thickness was determined for all twelve 30-degree segments around the disc, and averaged for the segments corresponding to the 6, 7, 8, 9, 10, 11 and 12 o'clock position. Correlations were verified with Pearson's correlation coefficients and linear regression analysis.

RESULTS

Both mfPERG amplitudes and OCT measurements were significantly smaller in eyes with temporal visual field defects than in normals. A significant and strong correlation was found between most mfPERG and macular or RNFL thickness OCT parameters.

CONCLUSIONS

mfPERG amplitudes and OCT measurements are significantly correlated in patients with chiasmal compression. Both technologies can quantify neuronal loss and, if used in combination, may help clarify structure-function relationships in this patient population.

[Current state of pupil-based diagnostics for glaucomatous optic neuropathy]

There are considerable differences between pupillary reactions to light in glaucoma patients and healthy subjects which can be identified by various techniques. These methods are based on the early asymmetry of the afferent conduction in the visual pathway, on the examination of the visual field by focal light stimuli or on visual stimuli in analogy with multifocal electrophysiological tests. Latest findings in pupillary research also suggest a possible use of the intrinsically photosensitive (melanopsin expressing) retinal ganglion cells in glaucoma diagnostics. The current results of pupillary experiments in glaucoma patients are encouraging for further research in this field because suitable objective screening methods for glaucoma are continually being sought.

[Stereometric parameters of the optic disc. Comparison between a simultaneous non-mydriatic stereoscopic fundus camera (KOWA WX 3D) and the Heidelberg scanning laser ophthalmoscope (HRT IIII)]

BACKGROUND

The Heidelberg retina tomograph (HRTIII, Heidelberg Engineering, Germany) in conjunction with the Moorfields regression analysis (MRA) allows monitoring for the progression of early damage to the optic nerve suspicious of early stage glaucoma. The confocal scanning laser ophthalmoscope provides clinicians with an objective and reproducible analysis of morphological parameters of the optic disc. Margins of the optic disc are approximated with a contour line to calculate the stereometric parameters leading to interobserver and intraobserver variability of the MRA. New devices enabling 3D fundus photography might be an alternative to the established HRT. It was the goal of this study to compare the methods by assessing the differences in the topographic parameters obtained by the HRT and the Kowa nonmyd WX 3D (2D/3D non-mydriatic retinal camera, Kowa, Japan) in a representative sample.

METHODS

This retrospective study included 45 eyes of normal patients, 40 eyes of patients with macropapillae and 45 eyes of glaucoma patients. Each patient underwent an HRT examination and fundus photography with the Kowa nonmyd WX 3D on the same day. Excluded from the study were eyes with hazy media (cornea, lens, vitreous) or refractive anomalies higher than >4 dpt or astigmatisms >2 dpt. Eyes with previous refractive surgery history or other retinal diseases affecting the optic nerve were also excluded from the study. Bland-Altman plots were used for statistical evaluation. Distribution of parameters was described by 95% confidence intervals (CI).

RESULTS

In normal eyes (n=45) a mean difference in the disc area of 0.33 mm(2) was found (95 % confidence interval CI: 0.22-0.43), in the cup-disc ratio (CDR) of 0.02 (95% CI: -0.06-0.14), in the cup volume of 0.03 mm(3) (95% CI: -0.04-0.01), in the rim volume of 0.04 mm(3) (95%-CI: -0.04-0.13) and in the maximum cup depth of 0.28 mm (95 %-CI: 0.34-0.23). All differences, except for the rim volume, were statistically significant (p<0.05). Patients exhibiting a macropapilla (n=40) displayed a mean difference of 0.03 mm(2) (95 % CI: -0.18-0.11) for the disc area, a difference in CDR of 0.09 (95% CI: -0.05-0.13), a difference in maximum cup depth of 0.28 mm (95% CI: 0.23-0.34) and a cup volume of 0.14 mm(3) (95%-CI: 0.10-0.18). In addition, there were no significant differences in rim volume (difference: -0.02 mm(3), 95% CI: -0.07-0.12) or in disc area. In glaucomatous eyes (n=45), the mean difference for cup area was 0.33 mm(2) (95% CI: 0.22-0.43), an area of 0.09 mm(2) (95% CI: 0.06-0.13) for the CDR, -0.03 mm(3) (95 % CI: -0.09-0.02) for the cup volume and 0.08 mm(3) (95% CI: 0.03-0.13) for the rim volume. Mean maximum cup depth difference was 0.25 mm (95% CI: 0.20-0.31). Mean differences in CDR, maximum cup depth and cup area were all statistically significant. The mean differences did not exceed the interobserver and intraobserver variability found in HRT measurements of other studies.

CONCLUSIONS

To the best of our knowledge this study is the first comparing optic disc parameters of HRT and 3D photography. Mean differences in stereometric parameters did not exceed the known interobserver and intraobserver variability. The combination of non-mydriatic fundus photography and optic disc analysis is a very attractive and time-saving method. However, before progression of early glaucoma can be monitored or suspected glaucoma can be appraised over longer time periods, further studies are needed to clarify test and retest variability.

Spatial distributions of on- and off-responses determined with the multifocal ERG

We studied the contribution of retinal on and off-mechanisms in the multifocal electroretinogram (mfERG) by measuring responses to saw tooth stimuli. Six healthy subjects participated in this study. Rapid-on and rapid-off sawtooth stimuli with a period of 427 ms were presented in a multifocal pattern composed of 19 hexagons. The stimuli were interleaved with a blank field of the mean luminance and chromaticity. On- and off-responses were added to extract response asymmetries. The amplitudes of on-, off-, and added-responses were determined for different eccentricities relative to a signal baseline that was defined as the average of the electrical level recorded in two different time windows in which no responses were present. Measurements were repeated with eight different stimulus stretch factors to account for changes in retinal cell density as a function of eccentricity. The amplitudes of all ERG components decreased with increasing eccentricity for all stretch factors. For stretch factors between 0 and 20, responses to the central and immediately adjacent hexagons were large in amplitude. For more peripheral hexagons, the responses were very small or absent. Three components were identified in the on-responses (N20(on), P46(on) and N100(on)). In the offresponses, we found one positive (P20(off)) and one negative (N90(off)) component, whereas in the addition, three components (N20(add), P46(add) and N100(add)) could be observed. The N20(on) and P46(on) amplitudes decreased less steeply with eccentricity than the N100(on) amplitude, whilst the P20(off) and N90(off) amplitudes exhibited a similar decrease with eccentricity. In the addition, the two negative components exhibited a similar decrease in amplitude as a function of eccentricity and decreased more steeply than the positive component. The number of stimulated cones and retinal ganglion cells was estimated from anatomical data and compared with the responses. The spatial properties of the amplitudes of N20(on), P46(on), P20(off), and N90(off) and P46(add) were similar to those of the stimulated cone numbers. The remaining components had spatial characteristics that resembled those of the retinal ganglion cells. It is proposed that the ERG asymmetries revealed in the summed responses have post-receptoral origins, some of them reflecting the activity of the ganglion cell population. The use of sawtooth stimuli provide, similar to the pattern ERG, a way to record the ERG asymmetries.

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.

The multifocal pattern electroretinogram (mfPERG) and cone-isolating stimuli

The number of L cones in the retina normally exceeds that of the M cones. Because normal color vision does not depend on the ratio of L- and M-photoreceptors, their signals must undergo an alteration in gain before being analyzed in the cortex. Previous studies have shown that this gain must take place before the cortex, but after the bipolar/amacrine cell layer of the retina. The aim of this study was to obtain topographical information about L- and M-cone activity at the ganglion cell layer using multifocal pattern electroretinography (mfPERG). A standard (black and white) stimulus was used, as well as stimuli modulating only the long wavelength-sensitive (L) or only the middle wavelength-sensitive (M) cones. The L:M ratio was calculated from the amplitude of the L-cone isolating mfPERG to that of the M-cone isolating mfPERG of 10 trichromats. Both the positive and negative components of the waveform were analyzed. Additional recordings of single cone modulated mfERGs were obtained from nine of the 10 subjects. We also recorded from one protanope and one deuteranope. The L:M cone amplitude ratios for both deflections of the mfPERG in the trichromats were around unity (medians 1.18 and 1.16, respectively) for the central 8° of retina. In the peripheral retina between 12.8° and 26°, this ratio increased to 1.42 for the positive component, and 1.37 for the negative component. The median L:M cone amplitude ratios for the mfPERG were higher and ranged between 1.00–2.78 in the central 8° and 1.29–2.78 in the periphery. The results indicate that a major gain adjustment of the retinal signals takes place at the ganglion cell level, and that the ratio is higher at eccentric locations than in the central retinal area.

Slow pattern-reversal stimulation facilitates the assessment of retinal function with multifocal recordings

OBJECTIVE

The use of the multifocal pattern electroretinogram (mfPERG) for objective visual field testing is critically impaired by the small signal-to-noise ratios (SNRs) obtained. In order to explore ways to enhance mfPERG-SNRs and mfPERG-magnitude, the dependence of mfPERGs and multifocal visual evoked potentials (mfVEPs) on stimulation rate and stimulation mode is examined.

METHODS

Using VERIS Science 5.1.10X (EDI, CA, USA) mfPERGs and mfVEPs were recorded simultaneously in two different experiments to stimulation at 52 locations comprising a visual field of 44 degrees diameter. Firstly, in eight subjects the response magnitudes were compared for three pattern-reversal (PR) and two pattern-onset (PO) stimulus conditions, which differed in their maximal stimulation rate. Secondly, for equal recording durations the signal-to-noise-ratios (SNRs) of four PR stimuli with different stimulation rates were determined in eight subjects.

RESULTS

Both mfPERG and mfVEP response magnitudes were substantially enhanced for the lower stimulation rates. The greatest effects were obtained for the mfPERG-N95 to pattern-reversal stimulation, which was by a factor of 5.2+/-0.6 greater than that N95 for the standard condition (p<0.001). mfPERGs for a comparatively low stimulation rate, i.e., reversing its contrast with a probability of 50% only every 53 ms, yielded the greatest SNRs (1.42-fold greater than for the standard condition; p<or=0.002).

CONCLUSIONS

The enhancement of both mfPERG and mfVEP response magnitudes for slow stimulation suggests that retinal mechanisms contribute to this response enhancement and that slow pattern-reversal stimulation might facilitate simultaneous high-resolution mfPERG- and mfVEP-based visual field testing.

SIGNIFICANCE

The study suggests that mfPERG-based assessment of retinal ganglion cell function can be improved with stimulation sequences that are 2-4 times slower than the standard multifocal stimulus.

Pattern electroretinogram in glaucoma

PURPOSE OF REVIEW

Several studies have shown that the pattern electroretinogram, a direct, objective method of measuring retinal ganglion cell function, is altered early in ocular hypertension and glaucoma. Renewed interest in the pattern electroretinogram for early detection of pre-perimetric glaucoma has been sparked by noninvasive and reproducible methods of recording using skin electrodes.

RECENT FINDINGS

With the noninvasive pattern electroretinogram, response abnormalities have been detected in up to 50% of glaucoma suspects with normal standard perimetry. In early glaucoma (with either normal or high intraocular pressure), a reduction of intraocular pressure has sometimes yielded improvement in pattern electroretinogram amplitude. A prolonged steady-state stimulus presentation reduces the pattern electroretinogram amplitude and increases optic nerve blood flow in normal subjects, suggesting that sustained activity of retinal ganglion cells is physiologically associated with autoregulatory changes of the neural-vascular system. It is unknown whether this autoregulation is altered in glaucoma. The multifocal pattern electroretinogram does not seem to have an advantage over the pattern electroretinogram in the early detection of glaucoma. The photopic negative response of the diffuse flash electroretinogram has shown changes in glaucoma, but may not be able to detect retinal dysfunction in normal tension glaucoma.

SUMMARY

The pattern electroretinogram is a noninvasive, direct, objective method that may be useful to clinicians in detecting early retinal ganglion cell dysfunction in glaucoma suspects. The pattern electroretinogram may also optimize treatment strategies based on improvement of retinal ganglion cell function.

The clinical applications of multifocal electroretinography: a systematic review

Multifocal electroretinography (mfERG) is an investigation that can simultaneously measure multiple electroretinographic responses at different retinal locations by cross-correlation techniques. mfERG therefore allows topographic mapping of retinal function in the central 40-50 degrees of the retina. The strength of mfERG lies in its ability to provide objective assessment of the central retinal function at different retinal areas within a short duration of time. Since the introduction of mfERG in 1992, mfERG has been applied in a large variety of clinical settings. This article reviews the clinical applications of mfERG based on the currently available evidence. mfERG has been found to be useful in the assessment of localized retinal dysfunction caused by various acquired or hereditary retinal disorders. The use of mfERG also enabled clinicians to objectively monitor the treatment outcomes as the changes in visual functions might not be reflected by subjective methods of assessment. By changing the stimulus, recording, and analysis parameters, investigation of specific retinal electrophysiological components can be performed topographically. Further developments and consolidations of these parameters will likely broaden the use of mfERG in the clinical setting.

Pattern reversal ERG and VEP--comparison of stimulation by LED, monitor and a Maxwellian-view system

PURPOSE

Pattern stimulation is widely used to detect inner retinal dysfunction. In this work we describe a pattern stimulation technique with LEDs and compare the results with conventional methods.

METHODS

PERG and VEP were derived from three normal subjects. Three different techniques were used to generate a checkerboard pattern reversal stimulus: a 70 Hz monitor, a Maxwellian-view system equipped with a Xenon-arc lamp and a mechanical mirror system, and a LED array (Roland Consult) consisting of 100 white LEDs. Two kinds of luminance (125 and 340 cd/m2) and four temporal frequencies (4, 8, 12 and 24 reversals per second) were studied on three healthy subjects. Additionally, a luminance tuning experiment (30, 60, 90, 125 and 340 cd/m2) was performed on one subject.

RESULTS

Comparison of different stimulation techniques shows reproducible responses of PERG and VEP with all three methods. The LED array leads to slightly smaller amplitudes than both other techniques, which we ascribe to the design of the LED field. No difference of peak times or phases was noticed between different stimulation techniques. A luminance dependency of PERG and VEP is noticeable using stimulation with LED: with decreasing luminance we measured increasing peak times of PERG and VEP and decreasing amplitude of PERG.

CONCLUSION

We conclude that central retinal stimulation with checkerboard pattern reversal is possible with LED. It gives comparable results to monitor and Maxwellian-view system.

Multifocal pattern electroretinogram: cellular origins and clinical implications

PURPOSES

The purposes of this article are to gain insight into the cellular origins of the multifocal pattern electroretinogram (mPERG) and evaluate its potential for clinical use.

METHODS

mPERGs were recorded from four anesthetized monkeys before and after pharmacologic blockade of light-driven activity of inner-retinal neurons and from 55 normal human subjects (19-91 years) and six patients with glaucoma (43-77 years of age). Stimuli consisted of counterphase-modulated black and white triangles organized in 61-scaled hexagons with mean luminance 100 cd/m2 and 100% contrast. The stimulus array subtended 31 degrees vertically and 37 degrees horizontally at 48 cm. The amplifier cutoff frequencies were 3 and 100 Hz. Responses were grouped as quadrants and the first slice of the second-order kernel was analyzed.

RESULTS

The mPERG responses of monkeys and humans were similar. In the monkey responses, there was an early positive potential (P1) around 25 ms and a later positive potential (P2) found selectively in the nasal field quadrants around 31 ms. These responses were seen around 22 and 36 ms in the human responses. After blockade of inner-retinal activity in monkeys, P1 amplitude was greatly reduced at all retinal locations and P2 was eliminated. P1 and P2 amplitudes were significantly reduced in the glaucomatous eyes relative to amplitudes of age-matched controls. Reductions in the amplitudes of P1 and P2 could easily discriminate between glaucomatous visual field quadrants with and without behavioral sensitivity losses. However, these alterations are likely to reflect diffuse losses.

CONCLUSIONS

mPERG responses contain prominent contributions from inner-retinal neurons that can be reduced in glaucomatous eyes. These findings raise the possibility that the mPERG could be potentially useful in the objective estimation of neural damage in glaucoma. However, further refinement of recording techniques will be required if the mPERG is to be used to detect focal damage.

Pattern reversal ERG with LED-stimulation using cyclic summation technique

PURPOSE

Multifocal pattern reversal stimulation can be used to detect inner retinal dysfunction. Commonly, the stimulus is generated on a monitor using m-sequence technique. We describe a pattern reversal ERG evoked by LED arrays using cyclic summation (CS).

METHODS

One eye of eight healthy subjects was examined with an arrangement of 13 LED arrays. Each array consisted of 100 LEDs separated by thin walls. One of the fields was placed centrally, three fields each were placed above, below, left and right of the central field. CS technique at a temporal frequency of 16 reversals per second (RPS) was used for stimulation. Viewing distance was 30 cm, check size was 0.58 cyc/deg. Luminance of the bright fields was 340 cd/m2.

RESULTS

Fourier analysis was performed. Centrally, the amplitude of the 2nd harmonic wave was highest (0.87 microV). In the first paracentral fields, amplitudes were 0.28 microV (nasally), 0.21 microV (superior, inferior and temporally). In the second paracentral fields, amplitudes were 0.11 microV (nasally), 0.09 microV (superior), 0.13 microV (inferior) and 0.15 microV (temporally). With exception of the temporal field (0.1 microV), in the outermost fields no reproducible ERG response could be recorded.

CONCLUSION

Peripheral ERG responses to a pattern reversal stimulus can be recorded with LED stimulation using CS technique up to an eccentricity of 30 degrees. Responses are highest centrally and decrease with increasing distance to the centre.

Glaucoma follow-up by the Heidelberg retina tomograph--new graphical analysis of optic disc topography changes

BACKGROUND

The Heidelberg Retina Tomograph (HRT) is a commercially available instrument for the detection of glaucomatous damage by analysis of optic nerve head topography. The main purpose of the study was to investigate the ability of HRT to detect changes in optic disc topography indicating progression of optic neuropathy in eyes with open-angle glaucoma or, in eyes with ocular hypertension, conversion to open-angle glaucoma.

METHODS

Fifty-nine subjects (34 with ocular hypertension, 25 with glaucoma) from the glaucoma service at Sahlgrenska University Hospital were included in this study. One eye of each patient was selected. All participants underwent thorough clinical examination, including HRT, high-pass resolution perimetry (HRP), and optic disk photography. After a mean follow-up time of 50 months, patients were re-examined. Based on analyses of optic disc photographs and HRP, eyes were classified into one of two groups: progressive or stable. The differences between baseline and follow-up HRT parameters in the two groups were analysed. The topographic HRT change images were also compared after digital image processing. A pixel ratio was calculated defined as the ratio between the area of pixels representing deepening of the disc surface and the total disc area. Receiver operating characteristic (ROC) curves for HRT parameters and pixel ratio were compared.

RESULTS

In the group judged to have progressive optic neuropathy, a statistically significant change between baseline and follow-up examination was found for the following HRT parameters: cup shape measurement, classification index, the third moment in contour, cup/disc ratio, cup area, rim area, and area below reference). In the stable group no HRT parameters had changed significantly. A well-defined distinction between the two groups was found by comparing digitally processed HRT change images. The area under the ROC curve was larger for pixel ratio than for any of the HRT parameters.

CONCLUSIONS

The HRT is a useful tool for long-term follow-up of glaucomatous optic neuropathy. Digital image processing of HRT change images could facilitate the detection of progressive change.