Transient Pattern Electroretinogram Research Articles

A comprehensive dataset of pattern electroretinograms for ocular electrophysiology research

The Pattern Electroretinogram (PERG) is an essential tool in ophthalmic electrophysiology, providing an objective assessment of the central retinal function. It quantifies the activity of cells in the macula and the ganglion cells of the retina, assisting in the differentiation of macular and optic nerve conditions. In this study, we present the IOBA-PERG dataset, an extensive collection of 1354 transient PERG responses accessible on the PhysioNet repository. These recordings were conducted at the Institute of Applied Ophthalmobiology (IOBA) at University of Valladolid, over an extended period spanning nearly two decades, from 2003 to 2022. The dataset includes 336 records, ensuring at least one PERG signal per eye. The dataset thoughtfully includes demographic and clinical data, comprising information such as age, gender, visual acuity measurements, and expert diagnoses. This comprehensive dataset fills a gap in ocular electrophysiological repositories, enhancing ophthalmology research. Researchers can explore a broad range of eye-related conditions and diseases, leading to enhanced diagnostic accuracy, innovative treatment strategies, methodological advancements, and a deeper understanding of ocular electrophysiology.

Pattern Electroretinogram in Ocular Hypertension, Glaucoma Suspect and Early Manifest Glaucoma Eyes: A Systematic Review and Meta-analysis

To provide standardized confidence limits of the transient pattern electroretinogram (tPERG) P50 and N95 and steady state pattern electroretinogram (ssPERG) amplitudes in normal controls as compared to ocular hypertension (OHT), glaucoma suspect (GS), or early manifest glaucoma (EMG) eyes. The identification of standardized confidence limits in the context of pattern electroretinogram (PERG) might overcome the high intrinsic variability of the measure, and it might lead to a more intuitive understanding of the results as well as to an easier comparison of data from multiple tests, sites, and operators. The study protocol was prospectively registered on the International Prospective Register of Systematic Reviews (ID: CRD42022370032). A literature search was conducted on PubMed, Web of Science, and Scopus. Studies comparing PERG raw data in normal control eyes as compared to OHT, GS, or EMG were included. The risk of bias was assessed using the National Institute for Health and Clinical Excellence quality assessment tool. The main outcome was the P50, N95, and ssPERG amplitude difference between the control and the study groups' eyes. The standardized mean difference was calculated as a measure of the effect size for the primary outcome. A subanalysis was conducted based on the type of electrodes adopted for the PERG measurements (invasive vs. noninvasive). Of the 4580 eligible papers, only 23 were included (1754 eyes). Statistically significant amplitude differences were found in the P50, N95, and ssPERG amplitudes between normal controls and OHT, GS, and EMG eyes. The highest standardized mean difference values were observed in the ssPERG amplitude in all 3 sets of comparison. The subanalysis did not reveal any statistically significant differences between invasive and noninvasive recording strategies. The use of standardized values as the main outcome measures in the context of the PERG data analysis is a valid approach, normalizing several confounding factors which have affected the clinical utility of PERG both for individual patients and in clinical trials. Steady state PERG apparently better discriminates diseased eyes compared to tPERG. The adoption of skin-active electrodes is able to adequately discriminate between healthy and diseased statuses. Proprietary or commercial disclosure may be found after the references.

The electroretinography and optical coherence tomography data matching in patients with advanced stages of glaucoma

AbstractPurposeTo determine the specific changes in the parameters of electroretinography (ERG), reflecting various aspects of retinal ganglion cell (GC) function, and optical coherence tomography (OCT), and their correlations in patients with advanced stages of primary open‐angle glaucoma (POAG).MethodsThe study included 35 people (55 eyes) with stages II and III POAG, divided into two subgroups, and 28 healthy age‐matched individuals (32 eyes). Transient and stationary pattern‐electroretinograms (PERG) and photopic negative response (PhNR) were recorded according to the ISCEV Standards (RETIport/scan, Roland Consult). The thickness of the GC complex (GCC) of the macular region was assessed (Heidelberg Spectralis OCT). The correlation analysis of the GCC indicators and the ERG data was performed. Validation for normal data distribution was performed using the Shapiro‐Wilk test. The Student's t‐test was used to compare normally distributed independent samples. Correlation analysis was performed using Pearson's correlation coefficient.ResultsWe found a reduction in the amplitude of N95 and P50 waves of transient PERG, the stationary PERG, PhNR, and PhNR/b index, and an increase in the peak latency of the N95 and P50 in both patient groups (p < 0.05). A statistically significant thinning of all layers of the GCC was noted in all the studied sectors (p < 0.01). The most essential morphological/functional correlations we determined between the amplitude of stationary PERG and the thickness of the GCC (r > 0.8; p < 0.01). The results showed moderate correlation relationships between parameters of the transient PERG and GCC (r > 0.4; p < 0.01) and between the PhNR amplitude and GCC thickness (r > 0.5; p < 0.01).ConclusionsWe documented specific changes in the morphological and functional parameters of the inner retina in patients with advanced stages of POAG. The detected regularities can be used as clinical markers of the disease and monitor the efficiency of a chosen therapeutic strategy.

Amplitude-frequency characteristics of the retina under diffuse and pattern stimulation and new formalized signs of flicker and pattern electroretinogram

To obtain additional formalized signs of ERG responses to flicker and pattern stimuli by analyzing the amplitude-frequency characteristics of the retina. A photopic flicker ERG (FERG) and a transient pattern ERG (PERG) were recorded from healthy individuals and patients with glaucoma. Using the digitized FERG and PERG signals, the amplitude-frequency characteristics of the retina were studied. The results of diffuse and structured stimulation modeling in Matlab Simulink were used to identify the characteristics of retinal responses to rhythmic and pattern stimuli. The amplitude-frequency characteristics (AFC) of the retina were obtained for the first time. They objectively reflect its ability to convert spectra of stimulating signals into spectra of recorded ERG responses. Using the results of modeling, diffuse flicker and pattern stimuli we have identified features of retinal response in Matlab Simulink. Based on a simplified simulation model, a negative component (baseline drift) was detected in a healthy person's PERG and its effect on the results of retinal AFC evaluation was investigated. Polynomial approximation procedure of retinal AFC was performed for the first time allowing the use of coefficients of approximating polynomials as new formalized signs in diagnostics. AFC were shown to be an objective characteristic of retinal transfer properties, which depend on the type of stimuli acting on it, as well as on the etiology of the retinal disease.

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

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. 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. 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. 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.

Oxidative stress in the red blood cells of patients with primary open-angle glaucoma.

This study was designed to examine oxidative and antioxidative changes in the red blood cells (RBCs) of patients presenting with glaucomatous degeneration. The experimental design was a case-control study of strictly selected patients who required antiglaucomatous surgery during primary open-angle glaucoma despite relatively regulated intraocular pressure (IOP) (POAG group, n = 30) and patients who underwent an operation for nonpathological cataracts (cataract group, n = 25). The activities of total superoxide dismutase (SOD), glutathione peroxidase (GPX), and catalase (CAT), as well as the concentration of malondialdehyde (MDA), were measured. Glaucomatous damage was estimated from a transient pattern electroretinogram. Significant increases in GPX (p = 0.026) and CAT (p = 0.000) activity were noted in the RBCs of POAG patients compared to those of cataract patients. Although SOD was elevated in patients with POAG, the differences compared to cataract controls were not significant (p = 0.079). MDA concentrations were significantly increased in the glaucoma group compared to the cataract controls. An oxidative disorder primarily represented by catalase upregulation was observed during the course of glaucoma.

Distinctive morphological and functional changes in retinal ganglion cells associated with normal aging and early stage of glaucoma

Early diagnosis of primary open-angle glaucoma (POAG) is closely connected with detection of normal age-related changes in the retina. It is also essential to develop reliable methods for quantitative evaluation of retinal nerve fiber layer (RNFL) thickness and retinal ganglion cells (RGCs) structure and function as well as to extend opportunities for inter-instrumental comparisons. to assess the function of RGCs from parvo- and magnocellular pathways by means of pattern electroretinography and to evaluate the degree of retinal sensitivity loss and RNFL thickness using new methods of analysis in normal aging and the early stage of POAG. Four groups were formed: group 1 - young healthy participants, group 2 - aged controls, group 3 - glaucoma suspects, and group 4 - early-stage POAG patients. In all groups we investigated the MD and PSD indices of static computer perimetry (HEP, Heidelberg Edge Perimeter, SAP and FDF tests) and RNFL thickness provided by HRT III (Heidelberg Engineering). Pattern electroretinograms (PERGs) were recorded with the RETImap system (Roland Consult) at the check sizes of 0.8° and 16°. For steady-state and transient PERGs the 0.8°/16° and N95/P50 ratios were calculated, respectively. There was a statistically significant difference in PERG amplitudes to 0.8° checks (p=0.0001) and in 0.8°/16° ratios (p=0.0001) between the groups 1 and 2. Differences between the groups 2 and 3 as well as 3 and 4 were statistically significant only as to 0.8° checks (p=0.03 and p=0.001, respectively). Responses to 16° checks were alike in all groups. We have also applied original formulas to determine the relative loss of RGCs and their axons and the congruence coefficient for morphological and functional parameters in normal aging and the early stage of POAG. The discovered age-related PERG changes convincingly indicate a greater parvocellular RGC loss as compared to magnocellular. Thus, the PERG ratio (0.8°/16°) should be corrected for the subject's age. The proposed indices of relative decline in retinal light sensitivity and RNFL thinning have been shown to be useful for quantifying the loss of RGC bodies and axons in normal aging and early-stage glaucoma.

Relationship between transient and steady-state pattern electroretinograms: theoretical and experimental assessment.

We determined if the overlap of transient (tr) pattern electroretinograms (PERG(tr)) can explain the generation of the steady-state (SS) pattern electroretinogram (PERG(SS)), and investigated the relationship between the two types of responses. Slightly jittered pattern reversals were used to generate quasi SS (QSS) PERG(SS) responses from eight normal subjects, recorded using lower eyelid skin electrodes, at rates between 6.9 and 26.5 reversals per second (rps). Jittered quasi PERG(SS) were deconvolved using the frequency domain continuous loop averaging deconvolution method. Additionally, conventional PERG(tr) at 2.2 rps and PERG(SS) at each of the QSS stimulation rates were obtained from all subjects. Two synthetic PERG(SS) responses were constructed at each stimulation rate, one using the PERG(tr) obtained at that rate, and the other using the conventional 2.2 rps PERG(tr). Synthetic responses then were compared to the recorded PERG(SS) using amplitude, latency, and spectral measurements. Findings indicate that the PERG(SS) obtained at SS rates can be predicted using the superposition of deconvolved tr PERGs at each particular rate. Although conventional PERG(tr) can explain PERG(SS) obtained at rates below 15.4 rps (≥ 97% correlation), for higher reversal rates only deconvolved responses obtained at that rate can produce the recorded SS responses (96% vs. 65% correlation at 26.5 rps). The study shows that PERG(SS) results from the overlapping of tr PERG(tr) waveforms generated at that reversal rate. The first two peaks (N(SS) and P(SS)) of the PERG(SS) reflect N35 and P50 waves of the tr PERG(tr). The N95 amplitude is reduced at conventional (16 rps) SS rates, but contributes to the overall PERG(SS) amplitude.

Pattern electroretinogram in neuromyelitis optica and multiple sclerosis with or without optic neuritis and its correlation with FD-OCT and perimetry

To evaluate the ability of transient pattern electroretinogram (PERG) parameters to differentiate between eyes of patients with neuromyelitis optica (NMO), longitudinally extensive transverse myelitis (LETM), multiple sclerosis with optic neuritis (MS + ON), multiple sclerosis without optic neuritis (MS - ON), and controls, to compare PERG and OCT with regard to discrimination ability, and to assess the correlation between PERG, FD-OCT, and visual field measurements (VFs). Visual field measurements and full-field stimulation PERGs based on both 48- and 14-min checks were obtained from patients with MS (n = 28), NMO (n = 20), LETM (n = 18), and controls (n = 26). In addition, FD-OCT peripapillary retinal nerve fiber layer (RNFL) and segmented macular layer measurements were obtained and their correlation coefficients were determined. Compared to controls, PERG amplitude measurements were significantly reduced in eyes with NMO and MS + ON, but not in eyes with LETM and MS - ON. PERG amplitudes were significantly smaller in NMO and MS + ON eyes than in MS - ON eyes. PERG and OCT performance was similar except in NMO eyes where macular thickness parameters were more efficient at detecting abnormalities. A significant correlation was found between N95 amplitude values and OCT-measured macular ganglion cell layer thickness, total retinal thickness, and temporal peripapillary RNFL thickness. PERG amplitude was also significantly associated with VF sensitivity loss. No statistically significant difference was observed with regard to the best-performing parameters of the two methods. Pattern electroretinogram measurements were able to detect RNFL loss in MS + ON and NMO eyes, with a performance comparable to OCT. PERG amplitude measurements were reasonably well correlated with OCT-measured parameters.

Pattern Electroretinography Changes in Patients with Established or Suspected Primary Open Angle Glaucoma.

ABSTRACTPurpose: To assess pattern electroretinogram (PERG) changes in patients with established or suspected primary open angle glaucoma (POAG).Materials and methods: Transient PERG using LV Prasad eye electrodes were performed in 76 normal, 32 glaucomatous and 22 glaucoma suspect eyes. The P50 amplitude, N95 amplitude and P50 latency were analyzed. The results were further analyzed with receiver operating characteristic (ROC) curves and discriminant function analysis (DFA).Results: The P50 and N95 amplitude of the POAG and glaucoma suspect groups were significantly reduced. There was significant shortening in the P50 latency in the POAG and glaucoma suspect groups. DFA using the P50 amplitude, N95 amplitude and P50 latency waveform parameters showed a sensitivity and specificity of 76.67 and 88.57% respectively.Conclusion: Pattern ERG demonstrated significant changes in POAG patients and suspects. ROC curves for the three wave parameters demonstrated that N95 amplitude was the better indicator for diagnosis of POAG when used individually.How to cite this article: Ganekal S, Dorairaj S, Jhanji V. Pattern Electroretinography Changes in Patients with Established or Suspected Primary Open Angle Glaucoma. J Current Glau Prac 2013;7(2):39-42.

Pattern ERG and RNFL thickness in hypertensive eyes with normal blue-yellow visual field

To evaluate the transient pattern electroretinogram (t-PERG) and the retinal nerve fiber layer (RNFL) thickness in eyes with ocular hypertension (OH) and normal short-wavelength automated perimetry (SWAP). In 26 patients with bilateral OH with normal SWAP, and in 26 age and sex matched healthy controls, t-PERG recording and RNFL thickness measurement were performed. Mean deviation (MD) and pattern standard deviation (PSD) of a reliable full threshold 24-2 SWAP were considered. RNFL thickness was determined by OCT3. Monocular PERG were recorded by using a black and white checkerboard pattern (check size 0.9°, contrast 100 %, mean luminance 80 cd/m2) generated on a monitor and reversed in contrast (four reversals per second, 2 Hz) at a distance of 70 cm. Patients had optimal correction at viewing distance; no mydriatic or miotic eye drops were used. Silver/silver chloride skin electrodes were placed over the lower eyelids in the stimulated eye (active electrode) and in the patched eye (reference electrode); ground electrode was in the Fpz scalp. Peak-to peak amplitude of P50 (N35-P50) and N95 (P50-N95) waves, and implicit time of P50, were considered. Compared to controls, in OH eyes, a reduction of N35-P50 amplitude (2.86 ± 1.49 vs. 3.77 ± 1.08 microvolts, -24.1 %, t-test p = 0.015), of average RNFL thickness (88 ± 11 vs. 96 ± 10 μm, -9.5 %, t-test p = 0.002), and of RNFL thickness in superior (p = 0.015) and inferior quadrant (p < 0.001), were found. Multivariate analysis showed that in OH eyes, N35-P50 amplitude was inversely related to intraocular pressure (IOP) (p = 0.001); no correlation was found between N35-P50 amplitude and MD, PSD, CCT or RNFL thickness. In OH eyes, both PERG and RNFL thickness changes occur in hypertensive eyes with undamaged SWAP; the correlation of PERG amplitude with IOP, but not with RNFL thickness, suggests that such PERG changes are an effect of the IOP on retinal ganglion cells, rather than a sign of their loss.

Retinal Pathway Origins of the Pattern Electroretinogram (PERG)

To determine retinal pathway origins of pattern electroretinogram (PERG) in macaque monkeys using pharmacologic dissections, uniform-field flashes, and PERG simulations. Transient (2 Hz, 4 reversals/s) and steady state (8.3 Hz, 16.6 reversals/s) PERGs and uniform-field ERGs were recorded before and after intravitreal injections of L-AP4 (not APB) (2-amino-4-phosphonobutyric acid, 1.6-2.0 mM), to prevent ON pathway responses; PDA (cis-2,3-piperidinedicarboxylic acid, 3.3-3.8 mM), to block activity of hyperpolarizing second- and all third-order retinal neurons; and TTX (tetrodotoxin, 6 μM), to block Na+-dependent spiking. PERGs were also recorded from macaques with advanced unilateral experimental glaucoma, and were simulated by averaging ON and OFF responses to uniform-field flashes. For 2-Hz stimulation, L-AP4 reduced both negative- and positive-going (N95 and P50) amplitudes in transient PERGs, and their counterparts, N2 and P1 in simulations, to half-amplitude. PDA eliminated N95 and N2, but increased P50 and P1 amplitudes, in that it enhanced b-waves. As previously reported, severe experimental glaucoma or TTX eliminated photopic negative responses, N95, and N2; glaucoma eliminated P50 and reduced P1 amplitude; TTX reduced P50 and hardly altered P1. For 8.3-Hz stimulation, L-AP4 eliminated the steady state PERG and reduced simulated PERG amplitude, whereas PDA enhanced both responses. TTX reduced PERG amplitude to less than half; simulations were less reduced. Blockade of all postreceptoral activity eliminated transient and steady state PERGs, but left small residual P1 in simulations. Transient PERG receives nearly equal amplitude contributions from ON and OFF pathways. N95 reflects spiking activity of ganglion cells; P50 reflects nonspiking activity as well. Steady state PERG, in contrast, reflects mainly spike-related ON pathway activity.

Dengue maculopathy: visual electrophysiology and optical coherence tomography

The objective of this study was to evaluate the visual loss due to dengue fever using retinal and cortical electrophysiology and retinal imaging. The participants were three female patients with low visual acuity after dengue fever. They were evaluated by routine ophthalmological investigations, transient pattern electroretinogram (tPERG), transient pattern visual evoked cortical potential (tPVECP), and retinal optical coherence tomography (retinal OCT). tPERG and tPVECP amplitude (microV) and implicit time (ms) were the parameters evaluated using OCT retinal thickness (microm) and reflectivity. All patients presented low visual acuity and scotomata with or without changes in the oculus fundus. tPERG from two patients showed decreased amplitude or absence of the main components; it was not possible to record a reliable response in the third patient due to excessive blinking. tPVECP at 0.5 cpd was normal in all three patients, while at 2 cpd the main components were absent in one patient and normal in the other two patients. OCT image was abnormal in two patients, one of them with high reflectance areas and another with decreased retinal thickness (the third patient was not studied with this technique).The dengue fever can lead to visual impairment detectable by ophthalmological exams such as angiography, retinography, and OCT imaging, as well as retinal and cortical electrophysiology. Dengue maculopathy which could be caused by vascular alterations and/or aberrant immune response after infection may result in temporary or permanent visual losses.

Pattern electroretinograms for the detection of neural loss in patients with permanent temporal visual field defect from chiasmal compression

To evaluate the ability of full-field and hemifield pattern electroretinogram (PERG) parameters to differentiate between healthy eyes and eyes with band atrophy (BA) of the optic nerve. Twenty-six eyes from 26 consecutive patients with permanent temporal hemianopic visual field defects and BA of the optic nerve from previous chiasmal compression and 26 healthy subjects were studied prospectively. All patients were submitted to an ophthalmic examination including Humphrey 24-2 SITA Standard automated perimetry. Full-field and hemifield (nasal and temporal) stimulation transient pattern electroretinograms (PERG) were recorded using checkerboard screens. Amplitudes and peak times for the P50 and N95 as well as the overall P50+N95 amplitude were measured. The intraocular N95:P50 amplitude ratio was calculated. Comparisons were made using Student's t-test. Receiver operating characteristic (ROC) curves were used to describe the ability of PERG parameters to discriminate the groups. Full-field P50, N95, and P50+N95 amplitude values were significantly smaller in eyes with BA than in control eyes (P < 0.001). Nasal and temporal hemifield PERG studies revealed significant differences in N95 and P50+N95 amplitudes measurements. No significant difference was observed regarding peak times or N95:P50 amplitude ratios. Nasal and temporal hemifield PERG values did not differ significantly in eyes with BA or in controls. Using the 10th percentile of normals as the lower limit of normal, 16 of 26 eyes were considered abnormal according to the best discriminating parameters. Transient PERG amplitude measurements were efficient at differentiating eyes with BA and permanent visual field defects from normal controls. Hemifield stimulation PERG parameters were unable to detect asymmetric hemifield neural loss, but further studies are required to clarify this issue.

Mercury toxicity in Amazon gold miners: Visual dysfunction assessed by retinal and cortical electrophysiology

Amazonian gold mining activity results in human exposure to mercury vapor. We evaluated the visual system of two Amazonian gold miners (29 and 37 years old) by recording the transient pattern electroretinogram (tPERG) and transient pattern visual evoked potential (tPVEP). We compared these results with those obtained from a regional group of control subjects. For both tPERG and tPVEP, checkerboards with 0.5 or 2 cycles per degree (cpd) of spatial frequency were presented in a 16° squared area, 100% Michelson contrast, 50 cd/m 2 mean luminance, and 1 Hz square-wave pattern-reversal presentation. Two averaged waveforms ( n=240 sweeps, 1 s each) were monocularly obtained for each subject in each condition. Both eyes were monocularly tested only in gold miners. Normative data were calculated using a final pooled waveform with 480 sweeps. The first gold miner, LCS, had normal tPERG responses. The second one, RNP, showed low tPERG (P50 component) amplitudes at 0.5 cpd for both eyes, outside the normative data, and absence of response at 2 cpd for his right eye. Delayed tPVEP responses (P100 component) were found at 2 cpd for LCS but the implicit times were inside the normative data. Subject RNP also showed delayed tPVEP responses (all components), but only the implicit time obtained with his right eye was outside the normative data at 2 cpd. We conclude that mercury exposure levels found in the Amazon gold miners is high enough to damage the visual system and can be assessed by non-invasive electrophysiological techniques.

Automatic positioning of cursors in the transient pattern electroretinogram (PERG) with very poor SNR using an Expert System

An expert system is described which automatically cursors PERG waveforms of very poor signal-to-noise ratio. The training data-set is derived from shape-perturbated PERG waveforms based on the ISCEV Standard and a series of clinically-normal waveforms. In validation trials, the Expert System is clearly shown to out-perform the Human Expert in the presence of noise. All software was written in MatLab((R)). It is proposed that this system is generic and similarly applicable to other transient recordings. A comprehensive Internet demonstration (SPoC: Smart Positioning of Cursors) is maintained at www.liverpooleye.org.

Wavelet feature space in computer-aided electroretinogram evaluation

The paper discusses creating a wavelet-based feature space for the classification of transient pattern electroretinograms (PERGs)--signals utilized in ophthalmology to evaluate the state of the retina. Discrete wavelet transform (DWT) can provide compact signal description, which is more accurate than time-domain data. A procedure for the proper choice of transform parameters is proposed. Both time-domain and wavelet features of these waveforms are visualized using principal components analysis. Separability of feature spaces is compared using k-means clustering algorithm. The results suggest that PERG waveforms are better separable when represented by DWT coefficients of full time-domain signal, than in traditional peak-based feature space.

Baseline characteristics of the transient pattern electroretinogram in non-human primates: inter-ocular and inter-session variability

This study assessed the inter-ocular and inter-session variability of the transient pattern electroretinogram (PERG) in a group of non-human primates. The transient PERG was measured both eyes of 29 non-human primates, and again after three months in 23 eyes of 23 of these animals. Signals were elicited using a contrast (90%, 75 cd m −2) reversing (5 reversals sec −1) checkerboard pattern (0·56 cpd). PERGs were also measured for stimuli of varied spatial frequency ( n=8, 0·07–2·22 cpd), contrast ( n=4, 20–100%), mean luminance ( n=4, 4·7–75 cd m −2) and defocus ( n=5, +1, +2, +3 diopters). The inter-eye and inter-session limits-of-agreement (LOA; 95%) were determined for each PERG parameter. Variability was also compared with previous studies using the coefficient-of-variability (COV). Pharmacological blockade of the inner retinal contributions to the PERG measured under these conditions was conducted in one animal using intravitreal injection of tetrodotoxin (∼6 μM) and N-methyl- d-aspartic acid (∼6 μM). The N95 component of the primate transient PERG showed spatial tuning, with a peak between 0·14 and 0·28 cpd. This spatial tuning was not as apparent for the P50 component. A linear relationship between P50 and N95 amplitude was found with contrast and mean luminance. Both components were attenuated with the introduction of +2 diopters or more of defocus. The inter-session COV for the P50 and N95 components were 23·8 and 19·2%, respectively, while the LOA were 58 and 46%, respectively. The N95:P50 ratio had smaller inter-session variability, was robust to changes in contrast, mean luminance and defocus, and was effective for characterization of inner-retinal dysfunction after pharmacologic block.

Evaluation of short-term increased intraocular pressure on flash- and pattern-generated electroretinograms of dogs.

To determine the electrodiagnostic and histologic response of short-term increases of intraocular pressure (IOP) on transient pattern electroretinograms (PERG) and flash electroretinograms (FERG) in the eyes of dogs. 8 healthy mixed-breed dogs. Transient PERG and FERG waveforms were recorded from dogs (while anesthetized) as IOP was increased from baseline (7 to 19 mm Hg) to 90 mm Hg. One hundred mean PERG responses and a single FERG response were recorded at each step during 3 recording sessions. Globes of each dog were enucleated after euthanasia on posttreatment day 7 and evaluated by a pathologist. Increases in spatial frequency resulted in decreased amplitudes of N2 (second negative PERG peak). Increases in IOP resulted in decreases in all 3 PERG waveforms and the FERG waveform. All values began to return to baseline after short-term increases in IOP on day 0, and waveforms were not significantly different on posttreatment days 3 and 7 Data suggest that short-term increases in IOP affect PERG and FERG waveforms, and PERG waveforms are more sensitive to increases in IOP Differences were not detected between treated and control eyes on histologic examination. Further studies are necessary to determine at what IOP permanent damage to ganglion and photoreceptor cells will develop and whether PERG is a reliable clinical diagnostic technique for use in dogs to reveal retinal damage that is secondary to increased IOP prior to changes in waveforms generated by FERG in dogs.

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

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