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

Pattern electroretinogram, blue-yellow visual evoked potentials and the risk of developing visual field defects in glaucoma suspects: a longitudinal "survival" analysis with a very long follow-up

PURPOSE

Estimating glaucoma suspects' risk for visual field defects helps to avoid under- and over-treatment. In this retrospective, longitudinal cohort study with a very long follow-up, we studied whether pattern electroretinograms (PERG) amplitudes and blue-on-yellow visual evoked potential (BY-VEP) latencies can predict visual field defects.

METHODS

Participants of the Erlangen Glaucoma Study were examined with PERG and BY-VEP between 9/1991 and 8/2001. Stimuli were created using an optical bench with Maxwellian view and consisted of vertical gratings (0,88 cpd) in a 32° field for both PERG and BY-VEP. Patients were treated according to clinical standards and performed standard automated perimetry (SAP) annually. Retrospectively, patients with normal SAP at baseline were selected. Primary endpoint was conversion to perimetric glaucoma. Predictive value was modeled using Kaplan-Meier analyses and a multivariate cox proportional hazards model with the continuous variables PERG amplitude, BY-VEP peak time and SAP square-root of loss variance (sLV) after stratification for Jonas classification of the optic discs.

RESULTS

Of 412 patients (288: Jonas 0, 103: I, and 21: II; baseline age: 20-60 years), 65 converted to perimetric glaucoma during follow-up (0.5-23.3 years; median 5.5 years). Optic disc classification was a strong risk factor for conversion (log rank p < 0.0001), and patients with more advanced changes progressed earlier. In the multivariate analysis (log rank p = 0.005), only PERG amplitude remained an independent risk factor after stratification for optic disc morphology (p = 0.021), with a ~ 30% higher risk per μV amplitude decrease.

CONCLUSIONS

PERG helps to estimate glaucoma suspects' risk for visual field defects.

Associations between steady-state pattern electroretinography and estimated retinal ganglion cell count in glaucoma suspects

Purpose

To estimate retinal ganglion cell (RGC) count in glaucoma suspects (GS) and ascertain its relationships with steady-state pattern electroretinography (ssPERG) parameters.

Methods

In this prospective cross-sectional study, 22 subjects (44 eyes) were recruited at the Manhattan Eye, Ear, and Throat Hospital. Subjects underwent complete eye examinations, optical coherence tomography, standard automated perimetry, and ssPERG testing. Eyes were divided into two groups based upon clinical data: healthy subjects and GS. RGC count was estimated using the combined structure–function index.

Results

Estimated RGC count, average retinal nerve fiber layer thickness (ARNFLT), and average ganglion cell layer and inner plexiform layer thickness (GCIPLT) were reduced in GS eyes (p ≤ 0.001 for all parameters). Pearson correlations revealed that ssPERG magnitude and magnitudeD correlated with ARNFLT (r ≥ 0.53, p < 0.001), GCIPLT (r > 0.38, p < 0.011), and estimated RGC count (r > 0.46, p < 0.002). Six mediation analyses revealed that estimated RGC count mediated the relationships among ssPERG parameters, ARNFLT, and GCIPLT.

Conclusion

Steady-state PERG parameters demonstrated linear correlations with estimated RGC count. The associations among ssPERG parameters and structural measures were mediated by estimated RGC count.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10633-022-09869-9.

Structure-function models for estimating retinal ganglion cell count using steady-state pattern electroretinography and optical coherence tomography in glaucoma suspects and preperimetric glaucoma: an electrophysiological pilot study

PURPOSE

To derive and validate structure-function models for estimating retinal ganglion cell (RGC) count using optical coherence tomography (OCT) and steady-state pattern electroretinography (ssPERG) parameters in glaucoma suspects (GS) and preperimetric glaucoma (PPG).

METHODS

In this prospective cross-sectional study, 25 subjects (50 eyes) were recruited at the Manhattan Eye, Ear, and Throat Hospital. Subjects underwent comprehensive eye examinations, OCT, standard automated perimetry (SAP), and ssPERG testing. Eyes were divided into three groups based on the Global Glaucoma Staging System: healthy (N = 30), GS (N = 10), and PPG (N = 10) eyes. The combined structure-function index (CSFI), which estimates retinal ganglion cell count (eRGC_CSFI) from SAP and OCT parameters, was calculated in each study subject. Two prediction formulas were derived using a generalized linear mixed model (GLMM) to predict eRGC_CSFI from ssPERG parameters, age, and average retinal nerve fiber layer thickness (ARNFLT) in 30 eyes selected at random (training group). GLMM predicted values were cross-validated with the remaining 20 eyes (validation group).

RESULTS

The ARNFLT, ssPERG parameters magnitude (Mag) and magnitudeD (MagD), and eRGC_CSFI were significantly different among study groups (ANOVA p ≤ 0.001). Pearson correlations demonstrated significant associations among ARNFLT, ssPERG parameters, and eRGC_CSFI (r² ≥ 0.31, p < 0.001). Two GLMMs predicted eRGC_CSFI from Mag (eRGC_Mag) and MagD (eRGC_MagD), respectively, with significant equations (F(3,18), F(3,19) ≥  58.37, R² = 0.90, p < 0.001). eRGC_Mag and eRGC_MagD in the validation group (R² = 0.89) correlated with eRGC_CSFI similarly to the training group. Multivariate pairwise comparisons revealed that eRGC_Mag and eRGC_MagD distinguished between healthy, GS, and PPG eyes (p ≤ 0.035), whereas independent Mag, MagD, and ARNFLT measures did not distinguish between GS and PPG eyes.

CONCLUSION

This pilot study offers the first combined structure-function models for estimating RGC count using ssPERG parameters. RGC counts estimated with these models were generalizable, strongly associated with CSFI estimates, and performed better than individual ssPERG and OCT measures in distinguishing healthy, GS, and PPG eyes.

Blue-Yellow VEP with Projector-Stimulation in Glaucoma

Background and aim

In the past, increased latencies of the blue-on-yellow pattern visually evoked potentials (BY-VEP), which predominantly originate in the koniocellular pathway, have proven to be a sensitive biomarker for early glaucoma. However, a complex experimental setup based on an optical bench was necessary to obtain these measurements because computer screens lack sufficient temporal, spatial, spectral, and luminance resolution. Here, we evaluated the diagnostic value of a novel setup based on a commercially available video projector.

Methods

BY-VEPs were recorded in 126 participants (42 healthy control participants, 12 patients with ocular hypertension, 17 with “preperimetric” glaucoma, and 55 with perimetric glaucoma). Stimuli were created with a video projector (DLP technology) by rear projection of a blue checkerboard pattern (460 nm) for 200 ms (onset) superimposed on a bright yellow background (574 nm), followed by an offset interval where only the background was active. Thus, predominantly S-cones were stimulated while L- and M-cone responses were suppressed by light adaptation. Times of stimulus onset to VEP onset-trough (N-peak time) and offset-peak (P-peak time) were analyzed after age-correction based on linear regression in the normal participants.

Results

The resulting BY-VEPs were quite similar to those obtained in the past with the optical bench: pattern-onset generated a negative deflection of the VEP, whereas the offset-response was dominated by a positive component. N-peak times were significantly increased in glaucoma patients (preperimetric 136.1 ± 10 ms, p < 0.05; perimetric 153.1 ± 17.8 ms, p < 0.001) compared with normal participants (123.6 ± 7.7 ms). Furthermore, they were significantly correlated with disease severity as determined by visual field losses retinal nerve fiber thinning (Spearman R = –0.7, p < 0.001).

Conclusions

Video projectors can be used to create optical stimuli with high temporal and spatial resolution, thus potentially enabling sophisticated electrophysiological measurements in clinical practice. BY-VEPs based on such a projector had a high diagnostic value for detection of early glaucoma.

Registration of study

Registration site: www.clinicaltrials.gov

Trial registration number: NCT00494923.

A Chronic Ocular-Hypertensive Rat Model induced by Injection of the Sclerosant Agent Polidocanol in the Aqueous Humor Outflow Pathway

Background: To induce a moderate chronic ocular hypertension (OHT) by injecting polidocanol, a foamed sclerosant drug, in the aqueous humor outflow pathway. Methods: Intraocular pressure (IOP) was monitored for up to 6 months. Pattern and full-field electroretinogram (PERG and ERG) were recorded and retinal ganglion cells (RGC) and retinal nerve fiber layer (RNFL) thickness were assessed in vivo with optical coherence tomography (OCT) and ex vivo using Brn3a immunohistochemistry. Results: In the first 3 weeks post-injection, a significant IOP elevation was observed in the treated eyes (18.47 ± 3.36 mmHg) when compared with the control fellow eyes (12.52 ± 2.84 mmHg) (p < 0.05). At 8 weeks, 65% (11/17) of intervention eyes had developed an IOP increase >25% over the baseline. PERG responses were seen to be significantly reduced in the hypertensive eyes (2.25 ± 0.24 µV) compared to control eyes (1.44 ± 0.19 µV) (p < 0.01) at week 3, whereas the ERG components (photoreceptor a-wave and bipolar cell b-wave) remained unaltered. By week 24, RNFL thinning and cell loss in the ganglion cell layer was first detected (2/13, 15.3%) as assessed by OCT and light microscopy. Conclusions: This novel OHT rat model, with moderate levels of chronically elevated IOP, and abnormal PERG shows selective functional impairment of RGC.

Neuroprotective Effects of Memantine in the Retina of Glaucomatous Rats: An Electron Microscopic Study

Purpose:

In this experimental study, the effects of systemic memantine administration on the retinal ultrastructure of experimentally induced glaucomatous rats were investigated.

Methods:

Twenty-four Wistar albino rats were included in this study. Glaucoma was induced by injecting sodium hyaluronate into the anterior chamber of the rats for a period of three weeks. As a control, 8 rats were sham treated (Group C). Glaucoma induced animals were divided into two groups; Group M (n = 8) received a single daily dose of 10 mg/kg memantine, and Group G received the same volume of saline (n = 8), via intraperitoneal route for a period of six weeks, starting with the induction of glaucoma. Then, all rats were sacrificed and the retinas were prepared for electron microscopic examination. Electron microscopic damage findings were graded between 0 and 4 and mean damage scores for each cell or layer was calculated for each group. Statistical comparison was made between group G and group M.

Results:

Including the photoreceptor cells, marked ultrastructural changes were observed in the retinas of the animals in group G. The ultrastructural changes in group M were modest and there was no significant cell death. Statistical findings indicated these results.

Conclusion:

Results of the present study suggest that memantine treatment, when started in the early phase of glaucomatous process, may help to preserve the retinal ultrastructure and thus prevent neuronal injury in experimentally induced glaucoma.

Hemifield pattern electroretinogram in ocular hypertension: comparison with frequency doubling technology and optical coherence tomography to detect early optic neuropathy

BACKGROUND

To assess the sensitivity and specificity of hemifield pattern electroretinogram (HF-PERG) for detecting early retinal ganglion cell (RGC) damage in ocular hypertensive (OH) patients.

METHODS

Fifty-two OH patients (mean age 56±9.6 years) with an intraocular pressure (IOP) .21 mmHg were assessed. All subjects underwent HF-PERG, optical coherence tomography (OCT), and frequency doubling technology (FDT) visual field.

RESULTS

OH patients showed a significant increase of peak-time of the N95 (P=0.027) compared to controls. The amplitude of the N95 of the lower and upper HF-PERG showed significant differences (P=0.037 and P=0.023, respectively) between the two groups. A significant intraocular (P=0.006) and interocular (P=0.018) asymmetry of N95 amplitude was found. Receiver operating characteristic (ROC) curve analysis revealed a sensitivity of 93% for the N95 of the lower HF-PERG, whereas full-field pattern electroretinogram (PERG) N95 peak-time had a sensitivity of 88%. In OH patients, we found a thinning of OCT - retinal nerve fiber layer (RNFL), especially in the superior and inferior quadrant, although not statistically significant, and a significantly higher FDT pattern standard deviation (FDT-PSD; P=0.001). In the OCT-RNFL inferior quadrant, a sensitivity of 82% was recorded. Finally, the sensitivity of the FDT-PSD was 92%.

CONCLUSION

Our study shows that HF-PERG is a very sensitive test for detecting early damage of the RGC.

Relationship between pattern electroretinogram, standard automated perimetry, and optic nerve structural assessments

PURPOSE

To examine the relationship between retinal ganglion cell function measured using pattern electroretinogram optimized for glaucoma screening (PERGLA), retinal nerve fiber layer (RNFL) thickness, and optic nerve head topography.

METHODS

Twenty-nine normal, 28 glaucoma, and 37 glaucoma suspect volunteers were enrolled. All participants were age similar. One randomly selected eye underwent complete eye examination, standard automated perimetry (SAP), scanning laser polarimetry with enhanced corneal compensation (GDxECC), optical coherence tomography, Heidelberg retina tomograph (HRT), and PERGLA measurements. PERGLA amplitude (microV) was converted to dB for comparison with SAP mean deviation (MD) and pattern SD. The correlation between PERGLA amplitude in dB and the average of sensitivity values for 16 central test locations of SAP were calculated. Analysis of variance, Pearson and Spearman rank correlations, coefficient of variation, and intraclass correlation coefficients were calculated.

RESULTS

PERGLA amplitude in glaucomatous eyes was significantly lower than normal eyes (0.47+/-0.20 vs. 0.70+/-0.28 microV, P<0.001) but not glaucoma suspects (0.54+/-0.21 microV, P=0.84). PERGLA amplitude was inversely correlated with age (r=-0.31, P=0.002). PERGLA amplitude (in dB) was associated with the sensitivity values of the SAP central 16 test locations (r=0.40, P<0001) across the entire cohort, GDxECC superior RNFL thickness (r=0.38, P<0.001), and HRT Moorfields regression analysis classification (rho=-0.34, P=0.001). The coefficient of variation and intraclass correlation coefficients were 14.5% and 0.89 for PERGLA amplitude, 2.4% and 0.98 for optical coherence tomography average RNFL, 2.2% and 0.97 for GDxECC temporal superior nasal inferior temporal average, and 6.3% and 0.94 for HRT rim area.

CONCLUSIONS

Retinal ganglion cell function measured using PERGLA is reduced in glaucoma and demonstrates modest correlations with central SAP sensitivity values and structural measures of optic nerve topography and RNFL thickness.

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.

Reproducibility of pattern electroretinogram in glaucoma patients with a range of severity of disease with the new glaucoma paradigm

PURPOSE

To determine the reproducibility of the pattern electroretinogram with the new Pattern Electroretinogram for Glaucoma (PERGLA) recording paradigm in glaucoma patients with a range of severity.

DESIGN

Experimental study.

PARTICIPANTS

Fifty-three glaucoma patients were recruited for the study (mean age +/- standard deviation [SD], 69+/-11 years). Their mean deviation (MD) global indices on static automatic perimetry ranged from 2.16 to -31.36 decibels (mean MD, -9.05).

INTERVENTION

All patients had pattern electroretinogram recordings done 5 times by the same operator, on 5 different days with the standardized PERGLA paradigm.

MAIN OUTCOME MEASURES

Pattern electroretinogram amplitude (microvolts), phase (pi radians), response variability (coefficient of variation [CV] = SD/mean x 100) of amplitude and phase of 2 partial averages that build up the pattern electroretinogram waveform, interocular asymmetry in amplitude and phase (in terms of the CV generated by the pattern electroretinogram software), signal-to-noise (S/N) ratio, SDs, CV, and intraclass correlation coefficient (ICC). All analyses were done on one eye of each subject, except when interocular asymmetry was studied.

RESULTS

The CVs of intrasession variabilities in amplitude and phase were 12.08% and 2.20%, respectively, and those of intersession variabilities were 20.82% and 4.17%. The pattern electroretinogram produced intersession ICCs in amplitude and phase of 0.791 and 0.765, respectively. These ICCs were significantly higher than the ICCs for pattern electroretinogram interocular asymmetry in amplitude and phase (0.659 [P<0.05] and 0.571 [P<0.05], respectively). On average, the pattern electroretinogram S/N ratio in glaucomatous patients was about 5:1.

CONCLUSIONS

The reproducibility of PERGLA in glaucomatous patients is sufficiently good for it to be considered a useful complementary clinical tool. Being more reproducible, direct measures of amplitude and phase should be more useful in monitoring progression than interocular asymmetry comparisons.

A new pattern electroretinogram paradigm evaluated in terms of user friendliness and agreement with perimetry

PURPOSE

To assess ease of use of the pattern electroretinogram optimized for glaucoma screening (PERGLA) paradigm by a novice operator; to study test-retest variability of the PERGLA parameters; and to compare results from the PERGLA to those from perimetry.

DESIGN

Cohort study.

PARTICIPANTS

Twelve healthy control subjects and 16 patients with moderate to advanced glaucoma in at least 1 eye.

METHODS

Pattern electroretinograms were recorded simultaneously from both eyes using a commercially available testing station. Each participant underwent PERGLA procedures in 2 sessions. One eye of each subject was tested on contrast sensitivity perimetry (CSP) in which a 0.4 cycles/degree Gabor patch served as a stimulus. Central visual fields results from conventional automated perimetry (CAP) were obtained from patients' records. Bland-Altman analysis was performed on PERGLA results to assess normal test-retest variability. Differences from mean normal (in decibels [dB]) were compared for PERGLA versus CSP and CAP.

MAIN OUTCOME MEASURES

Pattern electroretinogram amplitude, noise, phase, and test-retest variability (coefficient of variation); contrast sensitivity from CSP; perimetric sensitivity from CAP; and differences from mean normal for PERGLA, CSP, and CAP.

RESULTS

The mean log amplitude (0.08+/-0.12 log muV) and the mean phase (1.92+/-0.07 pi rad) for the control group were consistent with published PERGLA norms, as was test-retest variability for both amplitude (coefficient of variation [CV] = 8.2+/-7.0%) and phase (CV = 1.1+/-0.9%). The mean signal-to-noise ratio (8.7+/-4.5) was lower than published norms. The test-retest variability increased as PERGLA log amplitude decreased (R2>0.12, P<0.05). On average, differences from mean normal were similar for PERGLA versus CSP and for PERGLA versus CAP (mean differences<0.5 dB) with 95% confidence intervals near +/-4 dB in both comparisons.

CONCLUSIONS

A novice operator successfully replicated published PERGLA norms in a young control group for amplitude, phase, and repeatability. Higher test-retest variability was found in eyes with smaller signals. On average, PERGLA results were in reasonable agreement with those from perimetry, although there existed large individual differences which may limit the usage of PERGLA in screening or in following progression of glaucoma.

Slow-stimulated multifocal ERG in high- and normal-tension glaucoma

PURPOSE

To study the ability and sensitivity of the slow stimulation multifocal ERG (mfERG) to detect glaucomatous damage.

METHODS

Right eyes of 20 patients with normal-tension glaucoma (NTG), 15 patients with high-tension glaucoma (HTG) and 15 healthy volunteers underwent testing with the mfERG (VERIS 4.1). The central 50 degrees of the retina were stimulated by 103 hexagons (m-sequence: 2(13)-1, Lmax: 100 cd/m(2), Lmin: 1 cd/m(2), background: 50 cd/m(2)). Each m-sequence step was followed by 3 black frames (Lmax: < 1 cd/m(2)). Five response averages of the first order response component (KI) were analyzed: the central 7.5 degrees and the 4 adjoining quadrants. The amplitudes from the first minimum, N1, to the first maximum, P1, and from P1 to the second minimum, N2, were analyzed as well as the latencies of N1, P1, N2 and the latencies of 3 multifocal oscillatory potentials (mfOPs) with their maxima at about 73, 80 and 85 ms.

RESULTS

For each parameter the percentage of deviation from the mean of the control group was calculated. These values were then added for each individual to form a deviation index (DI). Seventeen patients (85.0%) with NTG and 3 patients (20.0%) with HTG showed a DI outside the normal range. The major changes were observed in the mfOPs of the NTG patients. MfOPs were then selectively filtered at 100-300 Hz and their scalar product was analyzed over an epoch of 68-105 ms. This confirmed that mfOPs differed significantly from the control in the central 7.5 degrees and, for NTG, in the nasal field. With a logistic regression analysis the mfOPs had a sensitivity to differentiate 85% of the NTG patients and 73% of the HTG patients from normal.

CONCLUSIONS

Under these conditions, the slow-stimulated mfERG can detect glaucomatous dysfunction in NTG (85.0%). The differences observed between NTG and HTG are in support of a different underlying pathomechanism.

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.

The decline of the photopic negative response (PhNR) in the rat after optic nerve transection

PURPOSE

To investigate the contribution to the photopic negative response (PhNR) of the electroretinogram (ERG) by retinal ganglion cells (RGCs). The PhNR was assessed longitudinally following optic nerve transection (ONTx).

METHODS

Photopic ERGs were recorded from each eye of an anesthetized (ketamine/xylazine, 60 mg/kg and 5 mg/kg) Brown Norway rat using custom made electrodes (PT-IR Tef., A-M System Inc). ERGs were elicited using green Ganzfeld flashes (11.38 scd/m(2), 22.76 cds/m(2)) and a rod suppressing green-background (40 cd/m(2)). PhNRs were compared before and after optic nerves were transected. Cresyl violet stained retinal flatmounts were used to estimate cell loss in the ganglion cell layer 3 and 15 weeks after optic nerve transection. The pharmacological effect of 1.3 microM intravitreal TTX on the PhNR was also evaluated.

RESULTS

There was a significant loss (p <0.05) in the PhNR of 20, 36, 34, 35, 48, 48 and 56% for ONTx eye versus the contralateral eye, at post ONTx times of 24 h, 1, 2, 3, 4, 8 and 15 weeks. B-wave amplitudes of ONTx eyes were not significantly different from the control eyes. In ONTx eyes, mean cell loss in the retinal ganglion cell layer was 27 and 55% at the 3 week and 15 week time periods. In the eyes with ONTx, the decline of PhNR amplitudes was correlated positively with RGC loss (r = 0.98; p < 0.01). Thirty minutes after intravitreal TTX injection, the PhNR was significantly reduced (57%, p<0.01).

CONCLUSIONS

There was a time-dependent decline in the PhNR after ONTx, as exemplified by a 35% reduction from 1-3 weeks, a 48% decline for 4-8 weeks and a 56% decline after 15 weeks. The correlation between the decline in the PhNR and retinal ganglion cell loss suggests that the PhNR depends on inner retina integrity and the PhNR may be important biological signal or detecting glaucomatous damage and the monitoring of RGC function changes in early glaucoma.

Pattern electroretinogram abnormality and glaucoma

PURPOSE

To determine the existence of retinal ganglion cell dysfunction and associated risk factors in glaucoma suspects with increased optic disc cupping and normal visual field.

DESIGN

Cross-sectional, observational study.

PARTICIPANTS

Two hundred glaucoma suspect (GS) patients were identified based on optic disc abnormalities (vertical cup-to-disc ratios [C/D]>0.5; vertical C/D asymmetry >or= 0.2; disc hemorrhages; notching) in association with known glaucoma risk factors (positive family history, African American descent, increased intraocular pressure [IOP]), but normal visual fields. Forty-two patients had early manifest glaucoma (EMG). Sixteen normal black subjects were added to update previous pattern electroretinogram (PERG) normative data and to establish a normal control (NC) group with a racial breakdown comparable with that of the study groups.

METHODS

Pattern electroretinograms were recorded simultaneously from both eyes using skin electrodes and automated analysis; visual fields were monitored with standard white-on-white automated perimetry (SAP) central 24-2 program; vertical C/D was evaluated by an independent reader from stereo disc photographs; and univariate and multivariate statistical analysis between PERG and other outcome measures was evaluated.

MAIN OUTCOME MEASURES

Pattern electroretinogram amplitude (microV), phase (pi rad), and interocular asymmetry in amplitude and phase (%); and SAP mean deviation (MD; decibels), vertical C/D, age (years), IOP (mmHg), and race (black vs. nonblack).

RESULTS

The PERG results were abnormal in at least 1 of the outcome measures in 52% of GS patients and 69% of EMG patients. The PERG amplitude was correlated weakly with both MD (P<0.01) and vertical C/D (P = 0.05). The correlation between PERG amplitude and MD and C/D was stronger (P<0.001) for interocular differences rather than absolute measures. Interocular PERG amplitude asymmetry increased with severity of disease (EMG>GS>NC; P<0.01). The PERG amplitude decline with age was steeper in patients with a more negative MD (P<0.01) and in patients with a more negative MD and a larger vertical C/D (P = 0.06). Black race (but not family history) was associated with lower PERG amplitude (P = 0.005) in GS and EMG patients, but not in normal controls (P = 0.44).

CONCLUSIONS

The correlation between PERG abnormality and known risk factors for glaucoma indicates that PERG has a predictive potential for the development or progression of the disease, or both.

Normative data for a user-friendly paradigm for pattern electroretinogram recording

PURPOSE

To provide normative data for a user-friendly paradigm for the pattern electroretinogram (PERG) optimized for glaucoma screening (PERGLA).

DESIGN

Prospective nonrandomized case series.

PARTICIPANTS

Ninety-three normal subjects ranging in age between 22 and 85 years.

METHODS

A circular black-white grating of 25 degrees visual angle, reversing 16.28 times per second, was presented on a television monitor placed inside a Ganzfeld bowl. The PERG was recorded simultaneously from both eyes with undilated pupils by means of skin cup electrodes taped over the lower eyelids. Reference electrodes were taped on the ipsilateral temples. Electrophysiologic signals were conventionally amplified, filtered, and digitized. Six hundred artifact-free repetitions were averaged. The response component at the reversal frequency was isolated automatically by digital Fourier transforms and was expressed as a deviation from the age-corrected average. The procedure took approximately 4 minutes.

MAIN OUTCOME MEASURES

Pattern electroretinogram amplitude ( micro V) and phase (pi rad); response variability (coefficient of variation [CV] = standard deviation [SD] / mean x 100) of amplitude and phase of 2 partial averages that build up the PERG waveform; amplitude ( micro V) of background noise waveform, obtained by multiplying alternate sweeps by +1 and -1; and interocular asymmetry (CV of amplitude and phase of the PERG of the 2 eyes).

RESULTS

On average, the PERG has a signal-to-noise ratio of more than 13:1. The CVs of intrasession and intersession variabilities in amplitude and phase are lower than 10% and 2%, respectively, and do not depend on the operator. The CV of interocular asymmetries in amplitude and phase are 9.8+/-8.8% and 1.5+/-1.4%, respectively. The PERG amplitude and phase decrease with age. Residuals of linear regression lines have normal distribution, with an SD of 0.1 log units for amplitude and 0.019 log units for phase. Age-corrected confidence limits (P<0.05) are defined as +/-2 SD of residuals.

CONCLUSIONS

The PERGLA paradigm yields responses as reliable as the best previously reported using standard protocols. The ease of execution and interpretation of results of PERGLA indicate a potential value for objective screening and follow-up of glaucoma.

The multifocal pattern electroretinogram in glaucoma

BACKGROUND

The pattern ERG can be used to detect early glaucomatous change, because the response of cells in the inner retina from (typically) 20 degrees -40 degrees of area is reduced before perimetric abnormality is certain. The multifocal pattern electroretinogram (mfPERG) allows analysis of many local regions within this area. The aim of this study was to investigate whether in patients with presumed glaucoma the mfPERG permits diagnosis and discrimination from normals.

METHODS

Measurements on 25 age-related normal eyes were compared to those on 23 eyes with different stages of glaucoma. A RETIScan system was used to generate a stimulus pattern of 19 hexagons, each consisting of six triangles. The triangles pattern-reversed black to white at 75 Hz. Those 19 hexagons were grouped into three stimulus regions: a central field, a middle, and a peripheral ring. The complete array subtended 48 degrees at the eye. The hexagons alternated between black and white, in a temporal pattern that followed a corrected binary m-sequence (length 512, 10 cycles with 39 s each). The amplitudes and latencies of positive responses at approximately 50 ms (P-50) and negative responses at approximately 95 ms (N-95) were analyzed.

RESULTS

In patients with glaucoma the P-50 and N-95 components of the mfPERG were significantly reduced for the central area and both outer rings compared to normal volunteers (p<0.001, Mann-Whitney-U). The most distinct reduction was observed for N-95 and the central ring. Changes in latencies were not conclusive. The reduction of the components increased with the stage of glaucoma. A predictive model for detecting early glaucomatous changes was designed based on P-50-N-95 with 88% sensitivity and 76% specificity.

CONCLUSION

In glaucoma a marked reduction of components, especially centrally is observed in the mfPERG. This hints to an early involvement of central ganglion cells and may be useful for future functional tests.

Sequential classification in glaucoma diagnosis

BACKGROUND

Large-scale screening in glaucoma diagnosis is expensive and time consuming. Sequential classification strategies can provide an effective combination of time-efficiency and diagnostic accuracy for glaucoma screening.

METHODS

In a cross-sectional clinical study, a sequential diagnostic strategy, based on several psychophysical and electrophysiological tests, was evaluated on measurements from 595 eyes from 310 patients with primary open-angle glaucoma, and 419 eyes from 213 control subjects (age range 18-70 years in each group). Patients and controls successively underwent up to five psychophysical and electrophysiological diagnostic tests. Optic disc morphometry was taken as gold standard. Adapting group sequential techniques, sensitivity and specificity for the whole diagnostic program were controlled, allotting overall error rates of 10%. The criteria for the diagnostic process were developed in a learning sample (677 eyes) and verified in a validation sample (337 eyes).

RESULTS

In the validation sample, 62.0% of the examined eyes could be classified, using a sequential 15-min two-step program. An overall 13.6% "gain" of saved time, compared to non-sequential discriminant analysis, was achieved without loss of diagnostic accuracy. A sequential 45-min five-step program classified 68.8% of the whole sample before morphometry, saving approximately 39% of examination time, compared to taking the complete discriminant score.

CONCLUSION

Especially in screening, where the use of time-consuming and complicated diagnostic procedures is restricted, the implementation of testing programs based on group sequential strategies might be a promising means of saving personnel resources and reducing inconvenience for patients.

The a-wave of the dark adapted electroretinogram in glaucomas: are photoreceptors affected?

AIMS

To evaluate whether the a-wave of the dark adapted flash electroretinogram (ERG) is affected by glaucomatous damage.

METHODS

ERGs were recorded in 20 patients (age 33-65 years) with advanced glaucomas (primary and secondary open angle and low tension glaucomas) and 20 normals using a ganzfeld stimulus. After 30 minutes of dark adaptation and pupil dilatation to at least 7.5 mm in diameter, luminance response functions were obtained presenting white flashes of increasing scotopic luminance (the highest flash intensity being 9.4 cd/s/m2, the lowest being 5.75 log units below it) with an interflash interval of 5 seconds. For each scotopic luminance, the responses of four flashes were averaged. The a-wave's amplitude was measured at 10, 11, and 12 ms. Within the glaucoma group, correlations between the interocular differences of the a-wave's amplitude and the mean deviation of a static perimetry (Octopus 500 perimeter, program G1) were computed for all flash intensities. Between normals and glaucomas, the a-wave's amplitude was compared for all flash intensities (paired t test).

RESULTS

Within the glaucoma group, the interocular differences of the a-wave's amplitudes correlated significantly with the differences of the MD for flash intensities of 9.4, 5.3, 1.7, and 0.5 cd/s/m2. The a-wave's amplitude was significantly lower in the glaucoma compared with the normal group (p <0.005) for flash intensities of 9.4 and 5.3 cd/s/m2.

CONCLUSION

These electrophysiological results imply that also the outer retinal structures, especially the photoreceptors, may be affected by glaucomatous damage.

Multifocal pattern electroretinogram does not demonstrate localised field defects in glaucoma

PURPOSE

To determine if a multifocal PERG could be recorded in normals, and to examine changes in the multifocal PERG in glaucoma patients. To compare the ability of multifocal PERG and multifocal VEP responses in the same individuals to identify localised field defects in glaucoma.

METHODS

Using the VERIS Scientific system multifocal PERGs were recorded from 19 sites of the visual field according to pseudo-random binary m-sequence. Twenty normals and 15 glaucoma subjects were tested. Multifocal pattern VEPs were also recorded in the glaucoma cases using a cortically scaled stimulus.

RESULTS

The second order kernel of the PERG shows a consistent signal. The overall PERG amplitude decreases with age in normals. In glaucoma the PERG amplitude was reduced across the field, but reductions did not correspond to the area of the scotoma. The VEP showed localised signal reductions in all 15 cases of glaucoma.

CONCLUSION

A multifocal PERG can be recorded in normals. However it did not reflect localised ganglion cell losses, whereas the multifocal pattern VEP recorded to a very similar stimulus in the same individual did show losses in the scotoma area.

The multifocal ERG in open angle glaucoma--a comparison of high and low contrast recordings in high- and low-tension open angle glaucoma

High and low contrast multifocal ERG (MF-ERG) recordings were obtained from the right eyes of 24 patients with OAG (high-tension OAG: n=16, low-tension OAG: n=8) and compaired to those recorded from 18 healthy volunteers. High contrast MF-ERG recordings were obtained at a mean luminance of 100 cd/m2 with a contrast of 99%, while low contrast MF-ERGs were obtained at a mean luminance of 100 cd/m2 with a contrast of 50%. During MF-ERG recordings the central 50 degrees of the retina were stimulated by 103 hexagons. A MF-ERG recording lasted eight minutes, a M-sequence of 2(15) was used. The first order response component (KI, mean focal flash response) and the first and second slice of the second order response component (mean focal two flash interaction of flashes one, KII. 1, or two, KII.2, base intervals apart) were analyzed for group differences. Group differences were found mainly in latency measures. These included a delay in the central response average of the first positive peak, P1, in KII.2 (p < or = 0.05) in OAG high contrast recordings. Low contrast recordings showed a significant delay in the central response average of the first negative peak, Nl, in KII.2 as well as in the peripheral response average of N1 in KI and of P1 in KII.2 (p<0.05) in OAG. Amplitudes were only affected significantly in KI of the low contrast recordings. Here the amplitude N1P1 was significantly higher in high tension (n=16) than in low tension (n=8) OAG patients. However, an overlap in all of the response parameters tested allowed only group differences to be characterized. Under these stimulus conditions, neither high contrast recordings nor low contrast recordings seem sensitive enough to reliably recognize early glaucomatous retinal dysfunction.

Statistical methods for the evaluation of diagnostic measurements concerning paired organs

Diagnostic measurements involving paired organs may be modelled using marginal or conditional approaches. Relevant information could be ignored by using marginal models with a mean structure not including information from the fellow organ. The conditional Rosner model can be generalized to a symmetric polychotomous logistic regression model. The rather strong assumptions of the Rosner model are relaxed in this symmetric model. The use of the symmetric model is justified by its relation to discriminant analysis. Additionally, the information of the diagnostic measurements from the fellow organ is taken into account explicitly. Furthermore, in case-control studies this approach corresponds to the sampling scheme. When the status of the fellow organ and the diagnostic measurement of this organ both are available, a surprising effect may be observed; pathological values of the diagnostic measurement from the fellow organ decrease the disease probability of the selected organ. As an example, four different diagnostic procedures from the Erlangen Glaucoma Registry are investigated.

Objective perimetry in glaucoma: recent advances with multifocal stimuli

The introduction of multifocal stimulus recording has enhanced our ability to examine the human visual field with electrophysiologic techniques. We have adapted the multifocal pattern visual evoked potential (PVEP) to detect visual field loss. In glaucoma patients we sought to determine the extent to which the PVEP amplitudes correlate with perimetric thresholds. Multifocal pseudorandomly alternated pattern stimuli, which were cortically scaled in size, were presented with use of the VERIS-Scientific system. Bipolar occipital straddle electrode positions were used. The visual field up to 25 degrees of eccentricity was investigated. Forty-three glaucoma patients with reproducible visual field defects were tested. The bipolar PVEP corresponded well with Humphrey visual field defects, showing loss of signal in the scotoma area. For Humphrey quadrant threshold totals and PVEP quadrant amplitudes, the correlation coefficient was strong (r = 0.49, P < 0.0001). The multifocal PVEP demonstrates good correspondence with the topography of the visual field. This technique represents the first practical application of the multifocal PVEP to objective detection of visual field defects in glaucoma.

Neuroprotection in relation to retinal ischemia and relevance to glaucoma

Management of glaucoma is directed at the control of intraocular pressure (IOP), yet it is recognized now that increased IOP isjust an important risk factor in glaucoma. Therapy that prevents the death of ganglion cells is the main goal of treatment, but an understanding of the causes of ganglion cell death and precisely how it occurs remains speculative. Present information supports the working hypothesis that ganglion cell death may result from a particular form of ischemia. Support for this view comes from the fact that not all types of retinal ischemia lead to the pathologic findings seen in glaucomatous retinas or to cupping in the optic disk area. Moreover, in animal experiments in which ischemia is caused by elevated IOP, a retinal abnormality similar to that seen in true glaucoma is produced, whereas after occlusion of the carotid arteries a different pattern of damage is found. In ischemia, glutamate is released, and this initiates the death of neurons that contain ionotropic glutamate (NMDA) receptors. Elevated glutamate levels exist in the vitreous humor of patients with glaucoma, and NMDA receptors exist on ganglion cells and a subset of amacrine cells. Experimental studies have shown that a variety of agents can be used to prevent the death of retinal neurons (particularly ganglion cells) induced by ischemia. These agents are generally those that block NMDA receptors to prevent the action of the released glutamate or substances that interfere with the subsequent cycle of events that lead to cell death. The major causes of cell death after activation of NMDA receptors are the influx of calcium into cells and the generation of free radicals. Substances that prevent this cascade of events are, therefore, often found to act as neuroprotective agents. For a substance to have a role as a neuroprotective agent in glaucoma, it would ideally be delivered topically to the eye and used repeatedly. It is, therefore, of interest that betaxolol, a beta-blocker presently used to reduce IOP in humans, also has calcium channel-blocking functions. Moreover, experimental studies show that betaxolol is an efficient neuro protective agent against retinal ischemia in animals, when injected directly into the eye or intraperitoneally.

The diagnostic significance of the multifocal pattern visual evoked potential in glaucoma

The concept of objective perimetry is an exciting one because it strives to assess glaucoma damage without relying on psychophysical testing. The recent introduction of multifocal stimulus recording has enhanced our ability to examine the human visual field using electrophysiology. A multifocal pattern visual evoked potential can now be recorded, testing up to 60 sites within the central 25 degrees. The test requires only that the subject fixate on a target, while a cortically scaled dartboard pattern stimulus undergoes pseudorandom alternation within each of the test segments. In its present configuration the test requires at least 8 minutes recording time per eye. Modified bipolar electrode positions are required to ensure that adequate signals are detected from all parts of the visual field. In glaucoma patients, pattern visual evoked potential amplitudes have been shown to reflect visual field loss with reduction of signal amplitude in the affected areas. This technique represents the first major step toward objective detection of visual field defects in glaucoma.

Mid-peripheral pattern electrical retinal responses in normals, glaucoma suspects, and glaucoma patients

AIMS

Reliance on intraocular pressure, optic nerve cupping changes, nerve fibre layer integrity, and visual field changes may delay treatment of glaucoma since irreversible changes may have already occurred at the time of diagnosis. Abnormal pattern electrical retinal responses (PERR or PERG) have been demonstrated in patients with ocular hypertension (no visual field changes) and glaucoma when visual stimulation was presented to the central field. Since glaucomatous visual field changes tend to occur first in the mid-periphery, the use of PERR outside of the central field may offer an earlier indication of glaucomatous involvement.

METHODS

Glaucoma suspects and glaucoma patients were derived from a university practice. Normal subjects were recruited from non-patient volunteers. Alternating bar gratings were presented in the supranasal, supratemporal, infratemporal, and infranasal visual field. Six spatial frequencies, from 0.25 to 6.0 cycles per degree, were used for normal volunteers; three spatial frequencies, from 0.38 to 1.5 cycles per degree, were presented to suspects and glaucoma patients. Time of onset of the first negative (N35) and first positive peak (P50) and the amplitude consisting of the absolute difference between the first negative peak and first positive peak (P50 amplitude) are reported. Age corrected values were determined for normals, suspects, and glaucoma patients for each spatial frequency and for each quadrant in the visual field.

RESULTS

Mean P50 amplitudes from normal subjects showed spatial tuning in all quadrants with reduced low frequency attenuation. Normals demonstrated a small decline in amplitude with age. Glaucoma patients demonstrated an age corrected reduction in amplitude and early implicit times. Glaucoma suspects had values between those of normal and glaucoma subjects. P50 amplitudes were weakly correlated with increasing cup to disc diameter ratio. A glaucoma patient with asymmetric visual field loss demonstrated significant diminution of the PERR bilaterally.

CONCLUSION

The PERR, using mid-peripheral stimulation, may be a sensitive tool for the early detection of glaucoma. Further refinements can speed clinical data acquisition and enhance signal to noise ratio.

Little correlation of the pattern electroretinogram (PERG) and visual field measures in early glaucoma

Pattern-electroretinograms (PERG) to checkerboard reversal at 16/s. 0.8 degrees and 15 degrees check size and visual fields (Octopus G1) were retrospectively analyzed in 40 eyes of 30 patients with early glaucoma. The mean visual field defect was calculated separately for the central 26 degrees x 34 degrees covered by the PERG stimulus (MDc) and the more peripheral area (MDp) surrounding the stimulus. Deeper field loss was correlated with a reduced pattern electroretinogram amplitude (p < 0.01 for both MDp and MDc), indicating that the pattern electroretinogram deteriorates as glaucoma advances. If the analysis was confined to those 18 eyes (16 patients) that had no field defect within the area covered by the PERG stimulus (normal MDc but abnormal MDp), 13 of these had an abnormal PERG amplitude (p < 0.001). The results suggest that the PERG can reveal impairment of ganglion cell function that is not detected by conventional perimetry.

Retest variability and diurnal effects in the pattern electroretinogram

Pattern electroretinograms were recorded to phase-reversing checkerboard stimuli with DTL electrodes under conditions close to those of the ISCEV pattern electroretinogram guidelines. Both transient (2 reversals/s) and steady-state (16 reversals/s) stimulation was used. The check sizes were 0.4 degree, 0.8 degree and 16 degrees; the mean luminance 45 cd/m2, the contrast 98%, and the field size 32 degrees x 27 degrees. In 42 eyes of 21 subjects, measurements were repeated at the same time of day after 1 week. For each eye, the intersession coefficient of variation was calculated as a measure of reproducibility. We found a coefficient of variation (+/- standard deviation) of 7% +/- 5% for the amplitude of the steady-state pattern electroretinogram, 9.5% +/- 7% for the transient pattern electroretinogram and 1.5% +/- 2% for the latency of the transient pattern electroretinogram. To assess the diurnal variability, during a 15-h period, three pattern electroretinograms were recorded in 10 subjects. No relationship was found between the P50 latency and the time of day. However, the mean amplitude showed a maximum in the morning (9:30 am) and a minimum in the afternoon (2:30 pm). This small effect (about 7%, p < 0.001) was more pronounced for N95 and steady-state amplitudes than for P50 amplitudes (p < 0.01). Diurnal contributions to the pattern electroretinogram ranged between 3% and 10%. We conclude that pattern electroretinogram amplitude reproduces within +/- 10% with a probability of 70%. The effect size of the diurnal variation is similar and might be relevant for longitudinal studies.

Quadrant pattern ERG with SLO stimulation in normals and glaucoma patients

BACKGROUND

The pattern ERG (PERG) is one of the promising methods for investigation of glaucoma and may detect it at an early stage. The purpose of this study was to test the usefulness of the scanning laser ophthalmoscope (SLO) as a stimulator for evoking quadrant PERGs under visual control in normal and glaucoma eyes.

METHODS

The helium-neon laser of a Rodenstock SLO was used for quadrant stimulation (18 degrees x 29 degrees pattern size), while an infrared laser visualized the eye's fundus. Steady-state pattern-reversal ERGs were recorded in response to stripe patterns (8.33 Hz, 0.5 cycles/deg) in four retinal quadrants. Corresponding visual field defects were determined with the Octopus perimeter (G1, peridata). The subjects were 28 controls and 34 glaucoma patients with visual field losses and papillometric defects.

RESULTS

Amplitudes of nasal retinal areas (which include the blind spot) are smaller than those of temporal ones, and temporal lower responses are the largest. PERG amplitudes of all quadrants are significantly reduced in glaucoma (sensitivity 82%, specificity 80%). The differences between upper and lower quadrant PERGs are correlated with the differences between localized visual field defects of the same areas, (r = 0.46, P = 0.02).

CONCLUSIONS

The study demonstrates the feasibility of the SLO system for evoking localized PERG in normals and patients and shows the reduction of quadrant ERG amplitudes in glaucoma using the laser system.

Newer visual function tests in the evaluation of glaucoma

Conventional visual field testing, with a uniform white-on-white stimulus, is used routinely to diagnose and follow patients with chronic open-angle glaucoma. Many investigators, however, believe that conventional perimetry may not detect the earliest visual dysfunction in patients with chronic open-angle glaucoma. Consequently, much research has been performed over the past decade to develop a visual function test which might diagnose chronic open-angle glaucoma earlier than conventional perimetry. This review discusses the mechanisms, clinical studies and the current usefulness of the most common new visual function techniques. These tests attempt to detect early glaucomatous visual loss, generally by placing the visual system under stress and by minimizing the influence of extensive functional redundancy in the retinal ganglion cell network due to widely overlapping receptive fields. Success of new visual function tests depends on the specificity and the sensitivity of the instrument, excellent patient acceptance, short test duration, standardization of techniques, and limited expense. In addition to searching for newer visual function tests to evaluate glaucoma, we should continue efforts to improve the diagnostic capability and shorten the test duration of conventional perimetry.

The effect of optical defocus on the pattern electroretinogram in normal subjects and patients with Alzheimer's disease

The pattern electroretinogram, thought to originate from the spatially sensitive inner retinal layers, was recorded in 16 patients with Alzheimer's disease and 16 age- and gender-matched control subjects under the following two test conditions: (1) optical defocus or inattention, without laser pointer, and (2) optical focus or attention, with laser pointer. By correcting for optical defocus with the laser pointer, control subjects increased their pattern electroretinogram amplitudes by 8% from a mean value of 2.65 microV (standard deviation, 1.12) to 2.87 microV (standard deviation, 0.93), whereas patients with Alzheimer's disease had a 19% increase in pattern electroretinogram amplitude from 2.20 microV (standard deviation, 0.86) to 2.62 microV (standard deviation, 0.64). By controlling for optical defocus, the coefficient of variation (standard deviation/mean) was reduced by 10% (from 42% to 32%) in normal subjects and by 14% (from 39% to 25%) in patients with Alzheimer's disease. A two-way analysis of variance (ANOVA) did not show a significant difference in amplitudes between populations, which indicates that the pattern electroretinogram may not be valuable in establishing an early diagnosis of Alzheimer's disease. In a second study conducted in 20 young, healthy normal subjects, plus lenses were used to defocus the checkerboard stimuli, before recording the pattern electroretinogram. We found that the pattern electroretinogram was extremely sensitive to optical defocusing such that the response amplitude decreased by 13% at 20/25 visual acuity and 19% at 20/30. Reduction of pattern electroretinogram amplitude caused by change in visual acuity is an independent source of artifact.(ABSTRACT TRUNCATED AT 250 WORDS)

Chronic ocular hypertension alters local retinal responsiveness

Electrophysiological responses of the retina and visual cortex to a series of grating stimuli (6-768 minutes of arc) were recorded in seven sessions using normal beagles, 21 sessions using beagles afflicted with inherited ocular hypertension, and 12 sessions using rhesus monkeys. A 15 degrees field centred around the animal's area centralis or fovea was used to stimulate the central retina. A 30 degrees field, centred on the same spot, was then used to stimulate the larger area. Two recording series were completed on each animal, with both field sizes presented in each recording session. The first recording took place 30 minutes after and the second 2 hours after the injection of thiamylal sodium. Only the signals from the toroidal 15 degrees of the retina of the hypertensive dogs were remarkably larger during the second recording (p = 0.001). No significant differences were found between the two recordings from the retinas of normal dogs or monkeys, nor were there any significant differences between the two recordings from above the cortex in any group. Several hypotheses are proposed to explain the basis for the interaction of thiamylal with the more peripheral retinal function in clinically glaucomatous dogs.

Utility of the color pattern-electroretinogram (PERG) in glaucoma

Pattern-onset electroretinograms (PERGs) with red-green color contrast (CC) and green-"black" luminance contrast (LC) stripe patterns (0.3 c/deg) were recorded in a group of 80 control subjects and in a group of 42 patients having glaucomas of varying etiology and severity. The PERG data were correlated with the results of static perimetry and optic disc morphometry. In the glaucoma group the PERG was reduced significantly and by relatively similar amounts with both CC and LC stimuli. A significant correlation of the PERG reduction with visual field loss was found only with the CC, not with the LC PERG. Correlations between PERG amplitudes and neuroretinal rim areas of the optic disk were similar for the LC and for the CC stimulus. The rather poor percentage of correct classification of controls and patients based on the PERG or the optic disc morphometry alone can be improved by two-dimensional discriminant analysis using both CC PERG and papillometry data.

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.