The pattern electroretinogram in glaucoma and ocular hypertension

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.

Hemifield-based analysis of pattern electroretinography in normal subjects and patients with preperimetric glaucoma

This prospective cross-sectional study investigated the visual function of preperimetric glaucoma (PPG) patients based on hemifield (HF) pattern electroretinogram (PERG) amplitudes. Thirty-two (32) normal subjects and 33 PPG patients were enrolled in control and PPG groups, respectively. All of the participants had undergone full ophthalmic examinations, including spectral-domain optical coherence tomography (SD-OCT), visual field (VF) examination and pattern electroretinography (PERG). The PERG parameters along with the HF ratios of SD-OCT and PERG were compared between the control and PPG groups. Pairwise Pearson's correlation coefficients and linear regression models were fitted to investigate the correlations. The PERG N95 amplitudes were significantly lower in the PPG group (P < 0.001). The smaller/larger HF N95 amplitude ratio of the PPG group was found to be smaller than that of the control group (0.73 ± 0.20 vs. 0.86 ± 0.12; P = 0.003) and showed positive correlations with affected HF average ganglion cell-inner plexiform layer (GCIPL) thickness (r = 0.377, P = 0.034) and with average GCIPL thickness (r = 0.341, P = 0.005). The smaller/larger HF N95 amplitude ratio did not significantly change with age (β =  - 0.005, P = 0.195), whereas the full-field N95 amplitude showed a negative correlation with age (β =  - 0.081, P < 0.001). HF analysis of PERG N95 amplitudes might be particularly useful for patients with early glaucoma.

Pattern Electroretinogram Parameters and their Associations with Optical Coherence Tomography in Glaucoma Suspects

Aim

To investigate whether steady state pattern electroretinogram (ssPERG) could identify retinal ganglion cell (RGC) dysfunction, and to assess the relationship between ssPERG with optical coherence tomography (OCT) measurements in glaucoma suspects (GS).

Materials and methods

This was a prospective cohort study of GS, identified based on suspicious optic disk appearance and glaucoma risk factors. Complete eye exam, Standard automated perimetry, OCT, and ssPERG were performed. Magnitude (Mag), Magnitude D (MagD), and MagD/Mag ratio were subsequently used in the correlation and linear regression analyses between ssPERG parameters and the RNFL, GCL/IPL, and macular thicknesses measurements.

Results

Forty-nine eyes of 26 patients were included. Mag and MagD were significantly correlated with the superior, inferior, and average RNFL thicknesses (avRNFLT). All ssPERG parameters were significantly correlated with the average and minimum GCL/IPL thicknesses and the inner macular sector thicknesses. Mag and MagD significantly predicted the superior, inferior, and avRNFLT in the regression analysis. All ssPERG parameters were predictive of GCL/IPL thickness in all sectors as well as the average and minimum GCL/IPL thicknesses. All ssPERG parameters were predictive of all inner macular sector thicknesses and MagD was also predictive of some outer macular sector thicknesses as well.

Conclusion

ssPERG has significant correlations with and is predictive of RNFL, GCL/IPL, and macular thicknesses in glaucoma suspects.

Clinical significance

ssPERG may serve as a useful objective functional tool for identifying and following the progression of disease in glaucoma suspects.

How to cite this article

Tirsi A, Wong A, Zhu D, et al. Pattern Electroretinogram Parameters and their Associations with Optical Coherence Tomography in Glaucoma Suspects. J Curr Glaucoma Pract 2022;16(2):96-104.

Role of Pattern Electroretinogram in Ocular Hypertension and Early Glaucoma

PURPOSE

To test whether pattern electroretinogram (PERG) can early detect retinal ganglion cells dysfunction in ocular hypertension.

DESIGN

Cross-sectional observational study.

PARTICIPANTS

The study included 3 groups: control, primary open-angle glaucoma (POAG) and ocular hypertension (OHT) groups with 30 eyes in each group.

MATERIALS AND METHODS

Visual fields were examined using automated perimetry with central 24-2 program. Optical coherent tomography (OCT) was done to assess the neuroretinal rim area, vertical cup/disc ratio, and average superior and inferior retinal nerve fiber layer thickness. PERG was recorded using skin electrodes. Amplitude and latency of P50 and N95 were documented.

RESULTS

PERG data: the mean P50 and N95 latency were significantly higher in the POAG group and the OHT group compared with the control group (P<0.001, <0.001, respectively). Also, the mean P50 and N95 amplitude were significantly lower in the POAG group and the OHT group compared with the control group (P<0.001,<0.001, respectively). In the POAG group, there was a significant negative correlation between PSD on one hand and P50 amplitude (r=-0.620, P=0.001) and N95 amplitude (r=-0.61, P<0.001) on the other hand. Also, the mean deviation was positively correlated with P50 amplitude (r=0.51, P=0.007) and N95 amplitudes (r=0.50, P=0.002). However, there was no significant correlation between PERG parameters and OCT parameters. In the OHT group, PERG parameters did not correlate with visual field and OCT parameters.

CONCLUSIONS

PERG can detect the dysfunctional, but still live retinal ganglion cells earlier than OCT in OHT cases, allowing the early start of treatment that can restore the ganglion cell function before irreversible damage occurs.

Structural and Functional Evaluations for the Early Detection of Glaucoma

The early detection of glaucoma is imperative in order to preserve functional vision. Structural and functional methods are utilized to detect and monitor glaucomatous damage and the vision loss it causes. The relationship between these detection measures is complex and differs between individuals, especially in early glaucoma. Using both measures together is advised in order to ensure the highest probability of glaucoma detection, and new testing methods are continuously developed with the goals of earlier disease detection and improvement of disease monitoring. The purpose of this review is to explore the relationship between structural and functional glaucoma detection and discuss important technological advances for early glaucoma detection.

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.

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

PURPOSE

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.

Psychophysical and electrophysiological testing in ocular hypertension

PURPOSE

The purpose of this study was to compare psychophysical and electrophysiological testings in early optic nerve dysfunction in a group of clinically asymptomatic subjects with suspect ocular hypertension (OHT).

METHODS

Forty eyes of 40 patients with suspect OHT and asymmetrical horizontal cup/disc ratio (0.2/0.4), 22 eyes of 22 patients with open-angle glaucoma (OAG), and 40 eyes of 40 healthy controls were evaluated by using frequency-doubling technology perimetry (FDT), contrast sensitivity (CS), pattern electroretinography (PERG), and pattern visual-evoked potentials (VEP). The VEP were elicited by checkerboard stimuli with large (VEP 120), medium (VEP 45), and small (VEP 15) checks; then the values of the amplitude (A) and latency (L) of P100 peaks were studied. Receiver operator characteristic (ROC) curves were calculated to determine the sensitivity, specificity, and optimal cutoff points of abnormal values. A logistic regression analysis was performed to determine which tests were providing the most useful information. In addition, Kruskal-Wallis test was performed to test the differences between the control group and the OHT group.

RESULTS

VEP P100 peak latency (VEP L15 and VEP L45) and amplitude (VEP A120), PERG N95 peak amplitude, CS at medium spatial frequencies (CS 4SF), and FDT pattern standard deviation (PSD) yielded the greatest sensitivity (85.0 to 60.0%) and specificity (80.0 to 60.0%) ratio, displaying the largest ROC curve areas; whereas PERG N95 peak latency ROC curve had the smallest areas. Kruskal-Wallis test showed that most diagnostic tests were able to differentiate the OHT group from the control group. Stepwise logistic regression analysis identified VEP L15 (p < 0.001), CS 4SF (p = 0.023), FDT PSD (p = 0.032), and VEP A120 (p = 0.072) as tests that could be useful to distinguish controls from OHT.

CONCLUSIONS

Our data confirm that psychophysical and electrophysiological tests are useful for early detection of patients at risk of developing OAG.

Frequency Doubling Technology vs Standard Automated Perimetry in Ocular Hypertensive Patients

Background:

Frequency doubling technology (FDT) perimetry measures contrast sensitivity. The magnocellular component of ganglion cells in human retina is isolated as a whole by the FDT stimulus. The aim of this study is to investigate the role of Humphrey Matrix threshold testing in the detection of early functional retinal impairment in ocular hypertensive patients compared to standard automated perimetry (SAP).

Methodology:

Forty hypertensive patients were enrolled in this longitudinal observational clinical study. Functional testing included randomly Humphrey Matrix perimetry and white-on-white Humphrey visual field perimetry. Ibopamine test was performed in all forty patients. The cut-off of 3 mmHg was considered positive for this provocative test.

Results:

Out of 40 patients, we included 21 in ibopamine positive group and 19 in ibopamine negative group. These two groups are sex- and age-matched. In ibopamine positive group the mean increase in IOP is 4.6 mmHg (ranging from 3 to 10 mmHg). Statistics showed that correlation between FDT and SAP was statistically significant in ibopamine negative group and not statistically significant in ibopamine positive group. Only one patient, coming from IBO + group, converted from ocular hypertension to glaucoma. All the other subjects remained stable in both groups without any therapy and visual field abnormalities.

Conclusions:

FDT showed to be more sensitive and specific than SAP mostly in detection of early visual field impairment in ocular hypertensive patients.

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.

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

PURPOSE

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.

METHODS

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.

RESULTS

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.

CONCLUSIONS

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.

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.

Correlation between morphological and functional retinal impairment in patients affected by ocular hypertension, glaucoma, demyelinating optic neuritis and Alzheimer's disease

In this article the correlations between the morphological evaluation of the nerve fiber layer (NFL) thickness (by OCT) and retinal functional assessment (by Pattern ERG recordings) performed in patients affected by ocular hypertension (OHT), glaucoma (OAG), demyelinating optic neuritis (MSON), and Alzheimer's disease (AD) are reported. In OHT eyes with ocular hypertension we observed that the inter-individual variation in NFL thickness is correlated with the variability of the PERG responses (the thinner the layer, the worse the visual function). In our OAG, MSON and AD eyes we observed a significant reduction in NFL thickness when compared with controls. In OHT, OAG, MSON and AD eyes abnormal PERG responses with delayed implicit times and reduced amplitudes were found. The impairment in the PERG parameters was significantly correlated to the reduction in NFL thickness. Our results suggest that in patients affected by ocular hypertension, glaucoma, demyelinating optic neuritis, and Alzheimer's Disease there is a reduction of NFL thickness evaluated "in vivo" by OCT, and this morphological involvement is correlated with electrophysiological responses assumed to be originating from the innermost retinal layers.

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 cdm(-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 cdm(-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 (approximately 6 microM) and N-methyl-D-aspartic acid (approximately 6 microM). The N95 component of the primate transient PERG showed spatial tuning, with a peak between 0.14 and 0.28cpd. 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.

Beyond visual acuity: new and complementary tests of visual function

Visual acuity is an essential component of the routine ophthalmic examination and the most common measure of visual function. There is increasing recognition, however, of the need to evaluate visual function beyond the limited extent afforded by visual acuity. The primary objective of this article is to introduce a variety of new and lesser-used techniques for measuring visual function that complement visual acuity assessment, each of which has been shown to detect visual dysfunction in patients with normal visual acuity.

Results of the betaxolol versus placebo treatment trial in ocular hypertension

PURPOSE

To determine whether treatment with betaxolol can delay or prevent the conversion from ocular hypertension to early glaucoma on the basis of visual field criteria, by means of a prospective, randomised, placebo-controlled trial.

METHODS

Three hundred and fifty-six ocular hypertensives were randomized to treatment with either betaxolol drops or placebo drops during the period 1992-1996. Each patient was followed prospectively with 4-monthly visits. Examination at each visit included visual field testing, intra-ocular pressure (IOP) measurement and optic disc imaging. Conversion to early glaucoma was defined on the basis of visual field change by AGIS criteria. An intent-to-treat analysis compared visual field conversion after 3 years in the treatment and placebo arms. Normal visual field survival analysis was also performed. The IOP characteristics of the two treatment groups were compared.

RESULTS

Two hundred and fifty-five patients completed the study, which ended in 1998, with a range of follow-up of 2-6 years. Sixteen (13.2%) of 121 patients in the placebo group converted to glaucoma, compared with 12 (9.0%) of 134 patients in the betaxolol group. The intent-to-treat analysis demonstrated no evidence of any difference in conversion rates between the betaxolol and placebo groups after 3 years. Visual field survival analysis demonstrated no significant difference between the betaxolol and placebo groups. The betaxolol-treated group had significantly lower post-treatment IOP values. Converters had significantly higher pre- and post-treatment IOP values than non-converters.

CONCLUSIONS

Betaxolol significantly lowered the IOP level compared with placebo. Conversion to glaucoma was found to be related to both the baseline and post-treatment IOP levels. However the intent-to-treat analysis did not demonstrate a statistically significant reduction in the conversion rate in the betaxolol-treated group.

Symptomatic abnormalities of dark adaptation in patients with EFEMP1 retinal dystrophy (Malattia Leventinese/Doyne honeycomb retinal dystrophy)

PURPOSE

To investigate the nature of symptomatic visual disturbance in patients with EFEMP1 retinal dystrophy in the absence of geographic atrophy or choroidal neovascularization.

METHODS

Patients presenting to a tertiary referral centre underwent clinical evaluation, fluorescein angiography, colour contrast sensitivity, focal, pattern, and standard electroretinography, electrooculography, scotopic threshold perimetry and dark adaptometry.

RESULTS

Clinical features included reduced central vision, difficulty passing from light to dark, and diffuse submacular and peripapillary deposits, which were hyperfluorescent by fluorescein angiography. Colour contrast thresholds were abnormal in all six patients studied and both pattern and focal electroretinograms were abnormal in five of six patients. The scotopic and mixed rod-cone single flash ERG was normal but two patients demonstrated reduced oscillatory potentials and one had borderline delayed 30 Hz responses. Scotopic thresholds were elevated and rod-mediated dark adaptation kinetics were markedly prolonged in all six patients when measured over the central visible confluent deposits.

CONCLUSIONS

In patients with EFEMP1 retinal dystrophy with confluent macular deposits, scotopic sensitivity is reduced and dark adaptation kinetics are prolonged over the macular deposits but are normal elsewhere. These results emphasize the localised nature of functional deficits in some patients with EFEMP1 retinal dystrophy and correlate well with the patient's visual symptoms. Symptomatic visual dysfunction may precede the development of clinically evident geographic atrophy or choroidal neovascularization in this disorder.

Electroretinographic abnormalities in a rat glaucoma model with chronic elevated intraocular pressure

The purpose of this study was to determine the ability of electroretinographic (ERG) measurements to document progression of the retinopathy in a rat glaucoma model. Thirty four rats with a chronic intraocular pressure (IOP) elevation induced in one eye by cautery of three episcleral/extra-orbital veins were studied in four separate groups. ERGs were recorded sequentially in Group A rats (n = 12) at baseline, and after approximately 20, 40 and 60 days of high IOP, and in three additional groups of rats (n = 6 or 10 per group) after approximately 58, 30 and 175 days of high IOP, respectively. Scotopic ERG parameters recorded simultaneously from both eyes in Group A rats were: a- and b-wave amplitudes, implicit times, oscillatory potential amplitudes (OPs) determined at three different light-flash intensities, and the light-adapted (photopic) ERG b-wave amplitude. In the other groups of rats, only scotopic ERG a-wave, b-wave and OP amplitudes were measured.In Group A rats that were followed sequentially, all the ERG parameters recorded with attenuated stimuli showed significant time-dependent changes in glaucomatous eyes relative to their contralateral normal eyes, with OPs showing the earliest significant difference after only 3 weeks of high IOP. When different groups of unilateral glaucomatous rats were compared beyond 8 weeks of elevated IOP only the OPs showed a continued decrease with time and good discrimination between glaucoma and normal eyes. Over a 25 week period of high IOP the scotopic OPs measured with attenuated light stimuli declined at the rate of approximately 1.5% per week and provided the best ERG measure to monitor progression of retinal pathophysiology in the vein-occlusion rat glaucoma model.

Correlation between optical coherence tomography, pattern electroretinogram, and visual evoked potentials in open-angle glaucoma patients

OBJECTIVE

[corrected] To correlate the nerve fiber layer (NFL) thickness and the visual function evaluated by electrophysiologic retinal and cortical responses assessed in open-angle glaucoma (OAG) eyes.

DESIGN

Prospective case-control study.

PARTICIPANTS

Thirty glaucoma patients (mean age, 47.1 +/- 7.15 years; refractive error range, +/- 2 spherical equivalent) with a mean deviation of computerized static perimetry (24/2 Humphrey, Dublin, CA) from -5 to -28 dB and intraocular pressure less than 21 mmHg on pharmacologic treatment and 14 age-matched control participants.

METHODS

Nerve fiber layer thickness was measured by optical coherence tomography. Retinal and visual pathway function was assessed by simultaneously recording pattern electroretinograms (PERGs) and visual evoked potentials (VEPs) using high-contrast (80%) checkerboard stimuli (the single check edges subtend 15 minutes of the visual arc) reversed at the rate of two reversals per second. Linear regression analyses were adopted to establish the correlation between NFL thickness and PERG and VEP parameters.

MAIN OUTCOME MEASURES

Nerve fiber layer thickness measurements in each quadrant (superior, inferior, nasal, and temporal) were taken and then averaged (12 values averaged) and identified as NFL overall, whereas the data obtained in the temporal quadrant only (three values averaged) were identified as NFL temporal. PERG P50 implicit time and P50-N95 amplitude and VEP P100 implicit time and N75-P100 amplitude were also measured.

RESULTS

In OAG eyes, we found a significant (P < 0.01) reduction in NFL thickness in both NFL overall and NFL temporal evaluations with respect to the values observed in control eyes. PERG and VEP parameters showed a significant (P < 0.01) delay in implicit time and a reduction in peak-to-peak amplitude. In OAG eyes, the NFL overall and NFL temporal values were significantly correlated (P < 0.01) with the PERG P50 implicit time and P50-95 peak-to-peak amplitude. No correlations (P > 0.01) between NFL values and VEP parameters were found.

CONCLUSIONS

There is a correlation between PERG changes and NFL thickness, but there is no correlation between VEP changes and NFL thickness in patients affected by OAG.

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.

Impaired visual function in glaucoma

OBJECTIVE

This work aims to evaluate whether glaucomatous visual field defects could be related to an impaired retinal function, to a delayed neural conduction in postretinal visual pathways, or both.

METHODS

Visual field by Humphrey perimeter (central 24-2 threshold test) and simultaneous recordings of visual evoked potential (VEP) and pattern electroretinogram (PERG) were assessed in 21 subjects with open angle glaucoma (POAG) and in 15 age-matched controls (C).

RESULTS

VEP: in POAG eyes we found P100 latency significantly (P<0.01) delayed when compared with controls and correlated with mean deviation (index of global visual field damage, MD) of 24-2 Humphrey perimetry (P<0.001); the P100 amplitudes were significantly (P<0.01) lower in POAG eyes than in control eyes and correlated with MD (P<0.001). PERG: POAG eyes showed P50 latency significantly (P<0.01) delayed when compared with controls and correlated with MD (P=0.002); the P50 and N95 amplitudes were significantly (P<0.01) lower in POAG than in control eyes and correlated with MD (P50: P=0.006; N95: P=0.002). Retinocortical time (RCT: difference between VEP P100 and PERG P50 latencies) and latency window (LW: difference between VEP N75 and PERG P50 latencies) were significantly (P<0.01) longer in POAG eyes than in control eyes and correlated with MD (RCT: P<0.001; LW: P<0.001). No significant correlations (P>0.05) were found between electrophysiological parameters and the corrected pattern standard deviation (index of localized visual field damage) of 24-2 Humphrey perimetry.

CONCLUSION

In patients with open angle glaucoma the reduction of the index of global visual field damage (MD) could be ascribed to two sources of functional impairment: one retinal (impaired PERG) and one postretinal (delayed RCT and LW). In the postretinal impairment, a postsynaptic degeneration at the level of the lateral geniculate nucleus could be suggested.

Pilot study of the multifocal electroretinogram in ocular hypertension

AIMS

To investigate the variation of retinal function in ocular hypertension (OHT) using the multifocal electroretinogram (MERG), that can objectively assess regional retinal responses using kernel analysis.

METHODS

Patients with OHT were recruited for 61 flash MERG recording. The first and second order kernel responses were analysed and compared with responses from a normal group. All the patients with OHT had full eye examinations and visual field analysis to ensure they had no ocular pathology, apart from high IOP (>/= 22 mm Hg).

RESULTS

In OHT, both the first and the second order kernel responses showed a reduction in magnitude compared with control values. The second order kernel responses showed larger relative reduction of amplitude than the first order responses. In addition, the macula showed a greater reduction in response than the periphery.

CONCLUSIONS

First order and second order kernel analyses are useful for detecting changes of retinal response in OHT. The second order kernel analysis is important in measuring the inner retinal activity and is an important factor in detecting the early glaucoma case. Diminished macular response may be a useful sign in early glaucomatous changes.

Effects of nicergoline on the retinal and cortical electrophysiological responses in glaucoma patients: a preliminary open study

PURPOSE

The retinal dysfunction and the delayed visual cortex responses shown by patients affected by glaucoma can be objectively assessed by Pattern Electroretinogram (PERG) and Visual Evoked Potentials (VEP) recordings. The present study aims to evaluate the effects of nicergoline on the retinal function and on the visual cortical responses in glaucoma patients.

METHODS

Sixty patients (mean age 44.6+/-3.7) with open angle glaucoma were enrolled. The patients were divided into two groups: NG Group, where 30 patients were treated with nicergoline (Cebran((R)), 2 cps day) for 30 days; and CG Group, where 30 patients were not treated. Simultaneous recordings of PERG and VEP were performed in NG patients at the baseline, at 30 days after treatment with nicergoline (day 30), and at 45 days from the end of the treatment (day 75). PERG and VEP were recorded in CG patients at the baseline and after 30 and 75 days. The visual stimulus for recording PERGs and VEPs was a checkerboard whose elements subtended a visual arc of 60' and 15' with a 70% contrast, and alternated at a frequency of 2 Hz.

RESULTS

At the baseline none of the electrophysiological parameters observed in NG Group patients differed (P>0.05) from those of CG Group patients. At days 30 and 75, in CG Group patients the values of the PERG and VEP parameters were unmodified (P>0.05) with respect to the baseline. In NG Group patients, the 30-day treatment period with nicergoline induced a significant (P<0.01) improvement of the PERG and VEP parameters. At day 75 all the electrophysiological parameters of NG Group did not differ significantly (P>0.05) from those at the baseline.

CONCLUSION

Treatment with nicergoline induces an improvement of the retinal function and of the visual cortical responses in patients affected by glaucoma. This effect disappears within 45 days after the suspension of the treatment.

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.

Cytidine-5'-diphosphocholine (citicoline) improves retinal and cortical responses in patients with glaucoma

PURPOSE

To evaluate the effects of cytidine-5'-diphosphocholine (citicoline) on retinal function and on cortical responses in patients with glaucoma.

DESIGN

Randomized clinical trial.

PARTICIPANTS

Forty patients with open-angle glaucoma were randomly divided into two age-matched groups: citicoline group ([GC] n = 25) and placebo group ([GP] n = 15).

METHODS

The GC patients were treated with Neuroton (citicoline, 1000 mg/day intramuscularly) for 60 days; GP patients were treated with placebo (physiologic solution with additives) for 60 days. After 120 days of washout (day 180), the GC patients were divided into two age-matched groups: in 10 patients (GC1 group) the washout was prolonged for a further 120 days; in 15 patients (GC2 group) a second 60-day period of citicoline treatment was followed by a second 120-day period of washout. At day 180, the washout was extended for another 180 days in GP patients. In all subjects, retinal and cortical responses were evaluated by simultaneous recordings of visual evoked potentials (VEPs) and pattern-electroretinograms (PERGs) at baseline, after 60 days, and after 180 days. At day 300, VEPs and PERGs were also evaluated in GC1 patients, and at 240 and 360 days in GC2 and GP patients.

MAIN OUTCOME MEASURES

Visual evoked potential parameters (P100 latency and N75-P100 amplitude); PERG parameters (P50 latency and P50-N95 amplitude); and intraocular pressure.

RESULTS

The GP patients displayed similar VEP and PERG parameters in all examinations performed. In GC patients, the treatment with citicoline induced a significant (P < 0.01) improvement of VEP and PERG parameters, and their values were significantly different (P < 0.01) with respect to those of GP patients (P < 0.01). Visual evoked potentials and PERGs, recorded in GC patients after washout, revealed that although there was a worsening trend, the electrophysiologic improvement was still maintained. After a second period of washout, GC1 patients had VEP and PERG parameters similar (P > 0.05) to baseline ones and to those of GP patients. In GC2 patients, a second period of citicoline treatment induced a further (P < 0.01) improvement of VEP and PERG parameters

CONCLUSION

Citicoline may induce an improvement of the retinal and of the visual pathway function in patients with glaucoma.

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.

The optic nerve head component of the human ERG

The local responses of the multifocal ERG reveal continuous changes in the second order waveforms from the nasal to the temporal retina. Scrutiny of these changes suggests the presence of an additive component whose latency increases with the distance of the stimulus from the optic nerve head. This observation led to the hypothesis of a contributing source in the vicinity of the optic nerve head whose signal is delayed in proportion to the fiber length from the stimulated retinal patch to the nerve head. The hypothesis was tested with two independent methods. In Method 1, a set of different local response waveforms was approximated by two fixed components whose relative latency was allowed to vary and the fit of this two component model was evaluated. In Method 2, two signals were derived simultaneously using different placements for the reference electrode. The placements were selected to produce a different ratio of the signal contributions from the retina and the nerve head in the two recording channels. The signals were then combined at a ratio that canceled the retinal component. Method 1 yielded an excellent fit of the two component model. Waveforms and latencies of the hypothetical optic nerve head component derived from the two methods agree well with each other. The local latencies also agree with the propagation delays measured in the nerve fiber layer of the monkey retina. In combination, these findings provide strong evidence for a signal source near the optic nerve head.

Neural conduction in the visual pathways in ocular hypertension and glaucoma

BACKGROUND

The aim of our work was to evaluate neural conduction in visual pathways in subjects with ocular hypertension and glaucoma.

METHODS

We assessed simultaneous recordings of pattern electroretinograms (PERG) and visual evoked potentials (VEP) in 16 subjects with ocular hypertension (OHT), in 16 subjects with primary open-angle glaucoma (POAG) and in 15 age-matched controls. The visual stimuli were checkerboard patterns (the check edges subtend 15 min of visual arc; contrast 70%) reversed at the rate of 2 reversals/s.

RESULTS

In OHT and POAG patients we found PERG and VEP latencies significantly longer than in controls. The P50-N95 PERG amplitudes were significantly reduced in OHT and POAG eyes. VEP amplitudes were significantly reduced in POAG eyes, while in OHT they were similar to controls. The retinocortical time (RCT; difference between VEP P100 latency and PERG P50 latency) was longer in POAG patients than in controls; no differences between patients with OHT and controls were observed. Moreover, we observed that in POAG the longer RCT was inversely related to the PERG amplitude.

CONCLUSION

Our results suggest that involvement of the innermost retinal layers in POAG is accompanied by slowed neural conduction in the visual pathways.

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.

Pattern electroretinogram and peripheral colour contrast thresholds in ocular hypertension and glaucoma: comparison and correlation of results

AIMS

Both pattern electroretinogram and peripheral colour contrast thresholds have been shown to be abnormal in glaucoma and ocular hypertension. This study evaluates each of these tests as tools for the early diagnosis of glaucoma, compares and contrasts the results, and examines the relation between the two tests in a large cohort of ocular hypertensive patients.

METHODS

Transient and steady state pattern electroretinograms and peripheral colour contrast thresholds were performed in 45 normal, 37 glaucomatous, and 206 ocular hypertensive eyes. The results were analysed using receiver operating characteristic curves, together with evaluation of sensitivity and specificity of the tests. The relation between the two tests was examined by direct statistical correlation of the results.

RESULTS

All tests showed high sensitivity and specificity for discriminating between normal and glaucomatous eyes. However, there was a significant difference between the two tests for the number of ocular hypertensives considered as abnormal. Forty per cent of ocular hypertensives had abnormal pattern electroretinogram compared with 30% with abnormal peripheral colour vision. Peripheral colour contrast thresholds showed a significant correlation with both transient and steady state pattern electroretinogram.

CONCLUSION

Both of these tests have been shown to be promising new tools for the early detection of glaucoma but the number of ocular hypertensive patients showing abnormal results is rather higher than expected considering the natural history of the condition. Sensitivity in ocular hypertension may be increased by using a combination of both tests. The significant correlation between these psychophysical and electrophysiological tests is discussed.

Flicker perimetry using a luminance threshold strategy at frequencies from 5-25 Hz in glaucoma, ocular hypertension and normal controls

A prototype automated flicker perimeter was used to investigate flicker luminance thresholds in glaucoma patients (n = 11), ocular hypertensives (high risk n = 10, low and intermediate risk n = 21) and normal controls (n = 10). Differential light sensitivity was measured for one eye of each subject using a flickering stimulus at frequencies of 5, 10, 15, 20 and 25 Hz at ten test locations of 1 degree in the arcuate and nasal regions of the central 50 degrees of the visual field using a 4-2 dB staircase. The glaucoma patients had significantly reduced sensitivities for all frequencies (p < 0.001) with minimum sensitivity at 15 Hz. The 'high risk' ocular hypertensives had significantly reduced sensitivities at 10 and 15 Hz (p < 0.02). At present the ocular hypertensive patients in this study show no abnormalities demonstrable by conventional automated static perimetry. These findings may represent the earliest of perimetric deficits in patients with glaucomatous optic neuropathy.

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

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

Electrodiagnostic evaluation of the visual system: the role of the clinician

Visual electrodiagnosis is a new discipline with a long history. The foundations include the disciplines of psychophysics, neurophysiology, electronics, computer science, statistics and medicine. However, with such a complex heritage, visual electrodiagnosis has taken a considerable time to evolve to its present form. Today visual electrodiagnostic assessment is relevant, not only for conditions primarily affecting the visual system, but also in more generalised pathological states in which eye changes may be a manifestation. Pressures for more refined and accurate diagnoses stem both from a continuing improvement in knowledge of disease processes by the medical profession and greater expectations on the part of patients seeking advice. Specialised investigative services such as electrodiagnosis, if these are appropriately funded and maintained, provide data to clinicians which is repeatable and objective, without resorting to invasive technology.

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

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

Gold foil electrodes: a two-center study of electrode reliability

Using the routine techniques employed at our two centers for recording pattern electroretinograms and a variety of methods, we investigated the reliability of the gold foil electrode over repeated uses. We found no significant difference between the pattern electroretinograms recorded with new electrodes and those that had had such extensive use in patients that they were believed unsuitable for further clinical use. We therefore continue to recommend the gold foil electrode for repeated use.