Assessment of macular function by multifocal electroretinogram in age-related macular degeneration before and after photodynamic therapy

The Role of mf-ERG in the Diagnosis and Treatment of Age-Related Macular Degeneration: Electrophysiological Features of AMD

INTRODUCTION

Age-related macular cegeneration (AMD) is the leading cause of visual dysfunction worldwide, affecting 9-25% of individuals between 65 and 75 years old.

METHODS

We have reviewed the published articles investigating the role of multifocal electroretinogram (mf-ERG) in the diagnosis and treatment of AMD.

RESULTS

Visual evoked potentials have revealed decreased amplitudes and higher latencies in patients with AMD, while the degeneration of photoreceptors and abnormalities of retinal pigment epithelium can be identified by electro-oculogram recordings. Moreover, ERG can detect the functional abnormalities observed in AMD and evaluate each therapeutic approach. The record of local electrophysiological responses coming from different retinal areas can be accurately performed by mfERG.

CONCLUSION

The accuracy of mfERG in detecting the degeneration of photoreceptors, as well the disturbances of macular function, could be useful both in the early diagnosis of AMD and the assessment of treatment efficacy.

Multifocal electroretinograms in age-related macular degeneration before and after photodynamic therapy

Purpose

To evaluate multifocal electroretinograms (mfERG) and macular retinal thickness before and after photodynamic therapy (PDT) for predominantly classic choroidal neovascularization (CNV) (classic type) and occult with no classic CNV (occult type).

Methods

Recording of mfERG and measurement of macular retinal thickness were performed before and after PDT in 19 patients (19 eyes) with the classic type and 24 (26 eyes) with the occult type. The evaluation items were the amplitude of the first negative wave (N1), the amplitude from the peak of the negative wave to that of the following positive wave (P1), and the peak latencies of the negative and positive waves.

Results

Compared with mfERG before PDT, that after PDT showed a significant decrease in the P1 latency in the central area (31.1±1.9 ms before and 29.6±1.6 ms after PDT) for the classic type and significant decreases in both the central (32.0±2.0 ms before and 30.5±2.4 ms after PDT) and peripheral (30.2±2.0 ms before and 29.5±2.0 ms after PDT) areas for the occult type. Optical coherence tomography showed significant decreases in macular retinal thickness in both groups (464 and 314 μm before and after PDT, respectively, for the classic type and 516 and 340 μm for the occult type).

Conclusions

After PDT, retinal function evaluated by mfERG improved for both the classic and occult types, and the recovery of P1 latency may be due to improvement in retinal edema.

Transitions of multifocal electroretinography in patients with age-related macular degeneration after combination therapy with photodynamic therapy and intravitreal bevacizumab

To compare the differences in color Doppler imaging (CDI) and pattern visual evoked potential (P-VEP) examinations between normal tension glaucoma (NTG) and hypertension primary open angle glaucoma (HTG) patients, and investigate the relation between flow velocities measured by CDI and P-VEP examination in NTG and HTG patients. Sixty NTG patients, 66 HTG patients and 44 control subjects underwent CDI evaluation of the ophthalmic artery (OA), short posterior ciliary artery (SPCA) and central retinal arteries (CRA). The peak systolic velocities (PSV) and end-diastolic velocities (EDV) and resistive index (RI) of all retrobulbar vessels were measured. The latency and amplitude of P100 in P-VEP were recorded from the three groups. The differences of CDI and P-VEP parameters among NTG group, HTG group and control group were compared by one-way analysis of variance. The correlations between CDI parameters and visual field indices, P-VEP and visual field indices, P-VEP and CDI parameters in NTG and HTG patients were evaluated by Pearson's correlation analysis. NTG and HTG patients had the lower EDV and higher RI in the OA, CRA and SPCA comparing with that of control subjects. NTG and HTG patients also had lower PSV in OA and CRA comparing with that of control subjects. There was no significant difference in the blood flow velocities and RI of all retrobulbar vessels between NTG and HTG patients. The latency of P100 in VEP delayed and the amplitude of P100 decreased in the NTG and HTG patients comparing with that of the control group. There was no significant difference in the latency and amplitude of P100 between the NTG and HTG patients. The RI of OA and SPCA were negatively correlated with the mean deviation (MD) values in the NTG and HTG patients. The RI of OA was positively correlated with the PSD value in the NTG and HTG patients. The MD values in the NTG and HTG patients were negatively correlated with the latency time of P100. The RI of OA was positively correlated with the latency time of P100 in NTG and HTG patients. The RI of OA was negatively correlated with the amplitude of P100 in HTG patients. No significant difference was found in the parameters of CDI and P-VEP between NTG and HTG patients. The certain parameters of CDI were correlated with P-VEP parameters in NTG and HTG patients.

The electroretinogram: a useful tool for evaluating age-related macular disease?

With an ageing population, the number of age-related macular disease (ARMD) cases will inevitably rise. This gives greater impetus for the need to identify the disease earlier and assess treatments to slow disease progression. Differing electroretinogram (ERG) modalities have been reviewed in relation to the objective assessment of retinal function in ARMD and for monitoring the effectiveness of clinical interventions. Conflicting results have been found with regard to the efficacy of ERG findings in the investigation of ARMD in previous years. The newer multifocal ERG paradigm provides spatial topographical information about retinal function in ARMD. It has shown promising results in monitoring effectiveness of clinical interventions and studies are continuing in this area. Better knowledge of retinal function in ARMD may lead to enhanced treatments at each phase of the disease.

Focal macular electroretinograms after photodynamic therapy combined with posterior juxtascleral triamcinolone acetonide

PURPOSE

Retinal function is commonly depressed transiently after photodynamic therapy (PDT). Additional treatment may prevent this impaired retinal function. The purpose of this study was to determine the changes in the focal macular electroretinograms (FMERGs) after PDT combined with TA for age-related macular degeneration.

METHODS

Thirty-four eyes that were successfully treated by PDT with a posterior juxtascleral injection of TA were studied. FMERGs, optical coherence tomography, and indocyanine green angiography were performed before and after the PDT.

RESULTS

The mean amplitudes of the FMERGs were not significantly decreased 1 week after PDT with TA (P > 0.05). The mean ratio of the FMERG b-wave 1 week after PDT to that before PDT was 1.09, with an indistinct hypofluorescence at the site of the PDT (18 eyes), and the ratio was 0.91 in the eyes with a distinct hypofluorescence border (16 eyes; P < 0.05).

CONCLUSION

The combined use of TA with PDT mitigated the depression of retinal function soon after PDT. However, there were cases of severe choroidal hypoperfusion corresponding to the site of the laser spot that impaired retinal function in comparison to cases with mild hypoperfusion. Even with severe choroidal hypoperfusion, the deterioration in retinal function was relatively mild, with the b-wave FMERG reduced by only 10%.

The role of the ERG in the diagnosis and treatment of Age-Related Macular Degeneration

Age-related macular degeneration (AMD) is affecting an increasing number of people, with 2.95 million people estimated to be affected in the USA by 2020. Possible preventive agents, such as vitamins and supplements have been studied and new treatment options for AMD have been developed in recent years. What role does electrophysiology play as a sensitive outcome measure? The most commonly used tests are the full-field electroretinogram (ffERG) and the multifocal ERG (mfERG). Test results from patients with AMD and reduced central vision need special attention in respect to fixation pattern, age-matched control data, and retinal luminance. Advantages, disadvantages and limitations of techniques will be considered, together with a review of published studies.

A method for investigating the temporal dynamics of local neuroretinal responses

Visual sensitivity improves with prolonged exposure to light. Global neuroretinal responses increase, but little is known about the dynamics of local retinal responses over brief time intervals after changes in light level. This study applies the time-slice multifocal electroretinogram (TS mfERG) paradigm for the measurement of local electrical responses of the human eye over brief time intervals. Sixty-one, localised retinal areas were assessed over 25 degrees of the visual field. Cone-mediated contributions to the time-slice waveform were established. The time-slice mfERG waveforms were similar in shape and timing for pre- and post-photopigment bleach conditions after saturation of rod-mediated responses, suggesting there was no rod-mediated intrusion in the waveform. The temporal dynamics of the mfERG components show that N1P1 amplitudes decrease with each successive time-slice probe, with larger amplitude responses in the central retina compared to nasal and temporal retina. The time-slice mfERG waveform is a technique for assessing the temporal dynamics of cone-generated neural responses over time. The data are interpreted in terms of the vascular supplies and lower-level visual adaptation mechanisms.

Deficits in the electroretinogram in neovascular age-related macular degeneration and changes during photodynamic therapy

PURPOSE

To describe the deficits in four electroretinography (ERG) modalities in patients with neovascular age-related macular degeneration (AMD). To describe the changes in these parameters during a course of verteporfin photodynamic therapy (PDT).

METHODS

Pattern (PERG), multifocal (mfERG) (19 segment simplified test protocol), flash ERG and flicker ERG were performed in patients with active neovascular AMD before PDT and compared to fellow eye controls using paired t-tests. Changes in ERG parameters during the 12 month treatment course were visualised using 95% confidence intervals of the median difference. The statistical significance of any changes was quantified using Wilcoxon signed ranks tests.

RESULTS

Fifty patients were recruited and followed. At presentation all ERG amplitudes were reduced with greater reductions in focal as opposed to global test protocols (P < 0.05). Over the 12 month course of PDT, PERG P50 amplitude showed a general downward trend and latency remained unchanged. mfERG p1 amplitude density showed an upward trend at six months before returning to baseline by 12 months. mfERG ring 2 amplitude density was significantly increased at 12 months compared to baseline (P = 0.010). Flicker ERG latency was significantly increased at six months compared to baseline (P = 0.015).

DISCUSSION

The simplified mfERG protocol was tolerated by this patient group, however, they found the full test protocol demanding. Large deficits in the retinal ERG function occur in neovascular AMD and involve retinal locations adjacent to as well as overlying choroidal neovascularisation (CNV). After PDT there is an improvement in electro-retinal function in retinal locations overlying the CNV.

The clinical applications of multifocal electroretinography: a systematic review

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

Intravitreal use of bevacizumab (Avastin) for choroidal neovascularization due to ARMD: a preliminary multifocal-ERG and OCT study

PURPOSE

To evaluate by MFERG and OCT the macular function before and after intravitreal use of bevacizumab (Avastin) in eyes suffering from CNV due to ARMD.

METHODS

Eighteen eyes with subfoveal CNV due to ARMD were studied before and after intravitreal use of bevacizumab with MFERG and OCT. The post treatment follow up was three months.

RESULTS

Before treatment, OCT shows an increase of the retinal thickening of the fovea and the electrical response densities in the fovea and parafovea were decreased in all patients. Three months after treatment, OCT showed a real resolution of the subretinal fluid. The electrical responses in the fovea and parafovea remained the same or slightly improved in some cases. The intraocular pressure remained normal and no inflammation was observed.

CONCLUSION

The intravitreal use of bevacizumab may provide anatomical correlates that support the concept of disease amelioration but the functional improvement of the macula three months after treatment is not obvious. However the method is promising and needs further evaluation.

Dynamics of Retinal Function after Multiple Photodynamic Therapies in Age-Related Macular Degeneration: A Report of Cases

PURPOSE

To monitor retinal function after multiple laser treatments by photodynamic therapy (PDT) with the multifocal electroretinogram (mfERG) in age-related macular degeneration (AMD).

METHODS

Five eyes of five subjects with AMD were investigated before the first and 1 month after each of three PDT treatments. Function was assessed using the cone- and rod-mediated mfERG, high-contrast distance visual acuity, central visual fields and contrast sensitivity. For each subject the local first-order mfERG results before treatment were used as a template and fitted against the local post-treatment results (Matlab, Mathworks).

RESULTS

We found transient reduction of the cone- and rod-mediated amplitudes between the first and second treatments but stable or improved mfERG function in four of five eyes for the cone-mediated mfERG and in all eyes for the rod-mediated mfERG after three treatments. Visual acuities and contrast sensitivities remained stable between treatments in four and two eyes respectively, whereas visual fields showed substantially higher mean defects in two subjects after all treatments.

CONCLUSION

As found in previous studies of the cone-mediated mfERG after one PDT treatment, objective function was stabilized after multiple treatments in this case report. Similarly, although poor at baseline, rod-mediated function was not further compromised. Transiently reduced amplitudes after 1 month possibly reflected choroidal hypoperfusion. A larger sample size is needed to confirm if additional evaluation using electrophysiological criteria might be helpful in re-treatment decisions during PDT.

Objective functional assessment of age‐related maculopathy: a special application for the multifocal electroretinogram

This paper gives a brief review of methods that assess objectively function in age-related maculopathy (ARM) with emphasis on a newer method, the multifocal electroretinogram (mfERG). In contrast to other electrophysiological tests, such as the full-field and focal electroretinogram (ERG) or the electro-oculogram (EOG), which measure summed responses from various cells from larger areas of the retina, the multifocal electroretinogram maps function locally with a resolution as small as four degrees within the central 30 degrees. By using different paradigms it can measure local cone- and rod-mediated functional impairment at early and late stages of ARM. This improved mapping and higher resolution of the posterior pole compared to other objective methods might lead to earlier detection of ARM. Its usefulness has been demonstrated in documenting the effects of treatment after established laser treatments, such as photodynamic therapy (PDT) and in documenting function after retinal pigment epithelial transplantation, a possible future treatment in late neovascular ARM.