Scanning laser ophthalmoscope-evoked multifocal ERG (SLO-mfERG) in patients with macular holes and normal individuals

AIMS

A scanning laser ophthalmoscope (SLO) has been used for multifocal electroretinography (mf ERG) measurements under simultaneous fundus monitoring. The aim of this study was to prove if the SLO-mfERG measurement reflects reliably the clinically registered underlying disease, and to demonstrate the importance of its main advantage, fixation monitoring.

METHODS

In all, 10 patients with macular hole stage II/III were included in the study, and 19 normal individuals served as the control group. The mf ERG device was combined with an SLO, which was used both as a stimulus and trigger unit as well as a fundus-monitoring system. Monitoring of the fundus was guaranteed by an infrared laser (780 nm). The stimulus matrix consisted of 61 hexagonal elements, covering 24 degrees of the posterior pole. We examined both, patients with macular holes and healthy individuals.

RESULTS

Compared to normal controls, patients with a macular hole (Gass stage III) showed a significant decrease in response density in the centre of the stimulus array, which correlated well with the morphological alteration observed by clinical examination. However, variation of response density of the central hexagonal area has been proved to be high.

CONCLUSIONS

SLO-mfERG is a feasible and reliable new technique to investigate macular function under simultaneous fundus control. The main advantage is that control of fixation can be used in order to obtain more reliable results that correlate well with visible fundus abnormalities such as in patients with macular holes. However, further investigations have to be performed in order to overcome sufficiently the problem of fixation instability.

Effects of intraocular injection of a low concentration of zinc on the rat retina

The main aim of this study was to investigate whether intraocular injection of low concentrations of zinc (no greater than 10 microM) aid the survival of ganglion cells in the rat retina after excitotoxic (NMDA) and ischemia/reperfusion injuries. We also determined whether low amounts of zinc cause any detectable retinal toxicity. Intraocular injection of NMDA caused substantial reductions in the mRNA levels of the ganglion cell-specific markers Thy-1 and neurofilament light (NF-L). Co-injection of 0.1 or 1 nmol zinc neither diminished nor exacerbated the effect of NMDA on the levels of these mRNAs. Likewise, ischemia/reperfusion caused significant decreases in the levels of Thy-1 and NF-L mRNAs and in the b-wave amplitude of the electroretinogram. These effects were not counteracted by injection of zinc. Intraocular injection of NMDA caused marked toxicological effects in retinal glial cells, including upregulations of cyclooxygenase-2 (COX-2), inducible nitric oxide synthase (iNOS), glial fibrial acidic protein (GFAP), basic fibroblast growth factor (FGF-2) and ciliary neurotrophic factor (CNTF). Interestingly, injection of 1 nmol zinc caused no changes in the levels of COX-2 and iNOS, yet produced similar, although quantitatively less pronounced, changes in FGF-2, GFAP and CNTF. The upregulations of FGF-2 and CNTF suggest that increasing zinc intake may benefit injured retinal neurons. However, this was not found to be the case in the present studies, perhaps due to the acute nature of the injury paradigms utilised.

Cyclic summation versus m-sequence technique in the multifocal ERG

BACKGROUND

The m-sequence technique is a typical tool for the multifocal ERG. The use of LEDs instead of a computer monitor enables a new technique that merits closer investigation: The cyclic summation technique. The aim of this study was to compare the two methods.

METHODS

Six normal right eyes were examined with the RETIscan system using DTL electrodes. With an LED array (display diameter 52 degrees, 103 segments, 1 foveal + 102 arranged in six concentric rings) we studied: (1). first order kernels (m-sequence); (2). 30-Hz flicker responses (m-sequence); (3). 30-Hz flicker responses (cyclic summation). The three methods were tested with a pattern of concentric rings generated by selective deactivation of LEDs (the central LED and rings 2, 4 and 6; rings 1, 3 and 5 remained active). In each case six cumulative measurements (40 s each) were made and stored separately. To determine the signal-to-noise ratio, the average mf ERG response to all active LEDs was divided by the average response to the inactive ones.

RESULTS

1. Using cyclic summation the signal-to-noise ratio exceeds the signal-to-noise ratio of both m-sequence-controlled stimuli about twofold. This implies also better spatial resolution with the cyclic summation technique 2. Since the signal-to-noise ratio increases faster with the cyclic summation technique than with the m-sequence technique, the gain of time in mf ERG can reach 80%.

CONCLUSION

As far as the signal-to-noise ratio and measuring time is concerned, the cyclic summation technique outmatches the m-sequence technique in mf ERG.

[Testing central retinal function with multifocal electroretinography before and after photodynamic therapy]

BACKGROUND

Photodynamic therapy (PDT) is applied for certain forms of choroidal neovascular membrane (CNV). The aim of this study was to investigate the effect of PDT on central retinal function as assessed by multifocal electroretinography (ERG).

METHODS

24 patients (25 eyes) with CNV (>50% classic 12 eyes) or occult (9 eyes) in age related macular degeneration (AMD) and CNV with pathological myopia (4 eyes) were treated by PDT using Verteporfin((R)). Before and a median of 6 weeks after therapy, central retinal function was examined using multifocal ERG (RetiScan, 61 hexagons, first-order response).

RESULTS

In the area of treatment,we found a tendency of the amplitude of the first positive deflection (P1) to decrease and of the implicit time to increase, but both effects were not statistically significant. These alterations were more pronounced in eyes with occult CNV and in myopia-related CNV. Amplitude reduction and implicit time prolongation could also be found in the areas represented by the multifocal ERG but not treated. There was no significant correlation between change in visual acuity after PDT and amplitude of the multifocal ERG.

CONCLUSION

The effects of PDT on retinal function seem to be moderate as assessed by multifocal ERG. An inherent problem of this investigation was the recruitment of nontreated patients as controls. Future goals are investigations of patients with repeated PDT and of long-term alterations in multifocal ERG after PDT.

A comparison of two patient-friendly ERG electrodes

The ideal electroretinography (ERG) electrode does not exist. In deciding which electrode should be used in clinical practice the capacity to provide reproducible waveforms, maximal amplitudes and minimal irritation to the patient's eyes are the most important characteristics. This study tested two patient friendly electrodes, the gold foil (CH Electrodes, UK) and the H-K loop (Avanta, Slovenia). Seventeen normal volunteers were subjected to three standard measurements namely flash ERGs under photopic and scotopic conditions and the transient pattern ERG (PERG). Each test followed the guidelines set by the International Society for Clinical Electrophysiology of Vision (ISCEV). It was found that the mean values of the flash ERG a and b wave amplitudes and the PERG P50 and N95 amplitudes from the gold foil electrodes were approximately a factor of two larger than those from the H-K loop. In addition most of the subjects (13/17) felt less discomfort with the gold foil electrodes. We reached the conclusion that gold foil electrodes are the electrode of choice because they provide good patient comfort, reasonably high amplitudes and relatively reproducible results.

Multifocal electroretinogram (mfERG) in a family with occult macular dystrophy (OMD)

BACKGROUND

Localized macular dysfunction, in Stargardt macular dystrophy for example, is frequently not detected by Ganzfeld electroretinography (ERG) but it may be detected by methods such as focal macular electroretinogram and pattern electroretinogram at the posterior pole of the eye or indirectly by recording of the visual evoked cortical potentials (VEP). The multifocal electroretinogram (mfERG) is a new diagnostic tool allowing analysis of local bioelectrical signals of circumscript areas across the macular region. Miyake recently described a type of macular dystrophy, which he termed "Occult Macular Dystrophy" (OMD) because of a normal fundus aspect and functional deficit even in aged patients. This is a case report about a family with a presumed OMD where mfERG demonstrated a central depression in the affected family members.

PATIENTS AND METHODS

Three members of a family with a suspected autosomal dominant trait complained of a reduced visual acuity since early childhood. The fundus of all patients appeared normal without signs of a maculopathy. The first order mfERG (ROLAND system) was recorded using 61 hexagons.

RESULTS

The signals arising from the macular region of the 6 eyes (3 affected family members) were selectively depressed while the signals from the paracentral area were much less impaired. Statistical analysis of the mfERG signals (concentric hexagon rings) confirmed the central depression with a better performance of the peripheral rings.

CONCLUSIONS

A new family with OMD is added to preceeding reports. A reduced visual acuity without visible fundus abnormalities may be misdiagnosed as amblyopia, optic nerve disease or nonorganic visual disorder. The mfERG offers the diagnostic tool to detect a circumscript retinal/macular dysfunction by a single procedure.

Flash electroretinography in standing horses using the DTL microfiber electrode

PURPOSE

The goal of our study was the evaluation of a practical method for the recording of flash electroretinograms (ERGs) in sedated, standing horses with the DTL microfiber electrode.

METHODS

The horses were sedated intravenously with detomidine hydrochloride (0.015 mg/kg). The pupil was dilated and the auriculopalpebral nerve was blocked. The ERGs were recorded with the active electrode on the cornea (DTL), the reference electrode near the lateral canthus, and the ground electrode over the occipital bone. The light intensities of the white strobe light were 0.03 cd x s/m2 (scotopic) and 3 cd x s/m2 (scotopic and photopic). Photopic and scotopic single flash and flicker responses to Ganzfeld stimulation were recorded. During the 20-min dark adaptation period the retina was stimulated every 5 min with the 0.03 cd x s/m2 single flash.

RESULTS

The median b-wave amplitudes and implicit times were 38 microV and 33 ms (photopic cone-dominated response), 43 microV and 63 ms (5-min dark adaptation), 72 microV and 89 ms (10 min), 147 microV and 103 ms (15 min), 188 microV and 109 ms (20 min, 0.03 cd x s/m2, rod response), and 186 microV and 77 ms (20 min, 3 cd x s/m2, maximal combined rod-cone response). A steady increase in amplitude and implicit time was noted during dark adaptation. No oscillatory potentials could be isolated.

CONCLUSIONS

The use of detomidine hydrochloride sedation and the DTL microfiber electrode allowed the recording of good quality ERGs. This protocol should permit the detection of functional problems in the retina without the risk involved with general anesthesia.

[Workshop on electroretinography and visual evoked potentials]

Studies of vision using electrophysiological techniques are tests which record functional alterations in very early phases of a disease. Full field flash ERG evaluates the integrity of the cones, rods and bipolar cells. It is obtained by photopsic stimulation with Ganzfeld and contact lens corneal electrodes or, alternatively, gold leaf or anchor electrodes. Five responses must be obtained: that of the rods, a maximum, oscillatory potentials, that of the cones and a flicker response. Pattern ERG is a response of the ganglionic cells, which is obtained by pattern reversal morphoscopic stimulation, with a bandwidth between 1 and 60 Hz. The fundamental waves (0.5 5 mV) are P50 (luminance) and N95 (pattern specific). This is of great value in the early diagnosis of glaucoma. VEP are electrical fields that are recorded in the calcarine cortex. They give information about alterations in the optic nerve, chiasm, radiations and cortex. Pattern VEP is obtained with a visual angle of between 13 and 14 . The fundamental wave P100 is evaluated according to its latency and amplitude, and by comparing it with a healthy eye. Flash VEP is only used on patients who do not collaborate or who present an opacity of media.

Blue cone electroretinogram amplitudes are related to dopamine function in cocaine-dependent patients

The objective of the study was to examine the relationship between an index of central dopamine function and electroretinographic (ERG) blue cone amplitudes in cocaine-dependent patients. Thus, 17 recently abstinent cocaine-dependent patients had an ERG performed. They also had a lumbar puncture for determination of cerebrospinal (CSF) concentrations of the dopamine metabolite homovanillic acid (HVA). It was found that patients who had reduced ERG blue cone b-wave amplitudes (<0.5 microV) had significantly lower concentrations of CSF HVA than patients who had ERG blue cone b-wave amplitudes greater than 0.5 microV. There was also a significant positive correlation between ERG blue cone amplitudes and CSF HVA concentrations. These results suggest the possibility that ERG blue cone amplitudes may be a neurobiologic marker related to central dopamine function in cocaine-dependent patients.

An apparatus for studying electroretinographic responses under conditions of space flight

This project has developed so as to include the total range of electroretinographic responses under conditions of space flight. We built two special containers which made stratospheric balloon flights. The second prototype carries the following specifications: Immobilisation of two frogs; Light stimulation by flashes; Special corneal electrodes; Amplification and recording system. There is almost no tissue damage after prolonged observation (several days) of the animals and the electroretinographic responses do not show any significant changes. Such an apparatus could be used as the basis for an assembly to be incorporated into Spacelab.

A sclerocorneal electrode for the study of the characteristics of primate vision under condition of space flight

We describe here a physiologically nonirritating sclerocorneal lens electrode of special design for making reproducible, low noise electroretinographic recordings on frogs and the rhesus monkey. The apparatus should be particularly useful in studying the effect of space flight factors on these responses in man.

A practical method to obtain reproducible binocular electroretinograms in dogs

We present a simple method to record highly reproduciblebinocular electroretinograms in dogs. Rod and cone electroretinograms were elicited in 60 Beagle dogs, with the use of two adjustable photostimulators, one directed at each eye, and maintained in position with the use of a special device. Data analysis revealed no significant differences in amplitudes between the right and the left eye for each animal and each recording session, thus attesting to the high reliability of our approach. In a few instances, however, small interocular timing differences were noted. The proposed approach could therefore be used not only in a clinical setup where the functional status of the two eyes is often needed to reach a diagnosis butalso in research projects, such as toxicological assays, where the experimentation is performed on one eye while the other is kept as control.

[Diagnosis of retinal diseases. Comparison between multifocal ERG and fundus perimetry - a case study]

BACKGROUND

There are new methods available for function testing of the macula, i.e. multifocal Electroretinography (mfERG) as well as fundus perimetry with the scanning laser ophthalmoscope (SLO). The value and clinical impact of these methods have still to be evaluated. We wanted to compare the results from patients having undergone both examinations.

PATIENTS AND METHODS

A total of 33 eyes from 25 patients (visual acuity 0.03-0.8) aged 14-79 years were examined using fundus perimetry with the SLO. In addition, multifocal ERG was performed in all eyes, where 61 local ERGs inside the 30 degrees visual field were recorded. We compared the depth of the scotoma with the reduction of the amplitudes during mfERG taking the fixation status into consideration.

RESULTS

Examination time was comparable for both examination techniques. There was good concordance for eyes with retinitis pigmentosa with only central response. In contrast, patients with juvenile macular dystrophy demonstrated different results with comparable size of the defect while sometimes an enlarged pathology during mfERG was observed. Correlation between pathology findings observed in mfERG and fundus changes was difficult due to the change of the point of fixation caused by central scotoma. In age-related macular degeneration correlation of the findings was less obvious.

DISCUSSION

The different setting with supra-threshold stimuli during ERG in contrast to near-threshold stimulus presentation during perimetry, might be the reason for differences even in the beginning of retinal diseases. In addition, reduced stability of fixation leads to artifacts during mfERG while it may be compensated for in fundus perimetry. Both methods are of additional value and demonstrate different results depending on the disease.

[The reproducibility of multifocal ERG recordings]

PROBLEM

Multifocal electroretinogram recordings (mfERG) can be used to detect a local dysfunction of the retina. In this study we tested both the intrasessional and inter-sessional reproducibility of mfERG amplitudes.

METHODS

MfERGs from 6 eyes of 6 normal subjects were recorded on two different days using DTL electrodes. The relative coefficient of variation ( RCV) was used to quantify the amplitude reproducibility. We tested the effect of (a) session (inter- vs. intrasessional), (b) recording duration (7.3 vs. 3.6 min), (c) trace type (hexagon traces vs. ring averages), and (d) amplitude definition (peak-trough analysis vs. scalar product) on RCV.

RESULTS

RCV was 6.5+/-0.4% (Mean+/-SEM, n=96) when averaged across all recording conditions and all subjects. The ANOVA showed a significant difference ( p=0.018) between hexagon traces and ring averages. Another significant effect ( p=0.016) occurred for the interaction of (a) and (b).

CONCLUSION

MfERGs can be recorded with a high degree of reproducibility even for short recording durations and single hexagon traces. As the factor (a) did not show a significant effect, the new placement of the DTL electrode in the second session does not necessarily increase the retest variability compared to a second recording within the same session.

[Follow-up on MEWDS by fundus perimetry and multifocal ERG with the SLO]

BACKGROUND

Most conventional techniques for examination such as perimetry or ERG may not be sensitive enough to detect functional alterations due to MEWDS precisely. We report on a follow-up performed by fundus perimetry and the new technique of multifocal ERG using the scanning laser ophthalmoscope.

PATIENT AND METHOD

A 24-year-old female patient (VA 0.2/0.8) was followed up for 7 weeks with these techniques as well as Octopus perimetry, fluorescence angiography, Ganzfeld ERG and biomicroscopy. Multifocal ERG stimulation (mfERG, Retiscan) was performed with the SLO.

RESULTS

Visual acuity improved from 0.2 to 0.8 and the central relative scotoma disappeared while a relevant increase of P1-wave amplitudes in mfERG could be observed.

CONCLUSION

Combining objective measurements from the fundus controlled SLO-mfERG and results from fundus perimetry enable good correlation of morphology and results, even for minor alterations of the macula only accessible by few established clinical examinations.

An instrument to investigate temporal processing mechanisms with the multifocal ERG

The multifocal ERG technique is a powerful method of studying the function of different areas of the retina. Display systems such as the CRT, which are commonly used for stimulation, are subject to limitations such as those imposed by the raster method of scanning. This work describes a novel stimulating display using LEDs that retains the established hexagonal areas but overcomes some of the limitations of the CRT display systems. The design and construction of the instrument is described together with some preliminary results.

[Multifocal ERG with confocal scanning laser ophthalmoscope. Comparison with monitor simulation]

BACKGROUND

Multifocal electroretinograms (mfERG) were recorded using a confocal scanning laser ophthalmoscope (cSLO) and compared to the results from conventional monitor stimulation.

METHODS

Single and repeated measurements were recorded from 23 normal subjects using the cSLO (Heidelberg Retina Angiograph, Heidelberg Engineering, Heidelberg) as well as a conventional monitor as stimulation devices. Laser power output was modified by various optical filters. The reliability of the method and agreement with the conventional monitor stimulation were determined.

RESULTS

CSLO recordings showed a high degree of variability. Reduction of laser power output improved the retinal response topography and characteristically modified response variations with each filter. Differences in amplitude size between cSLO and monitor recordings decreased with increasing amplitude levels. The results of repeated measurements showed considerable variation.

CONCLUSION

It is possible to use a cSLO as a stimulator for mfERG recordings. However, a relatively high degree of variability represents a significant limitation of this method. Appropriate reduction of laser power decreases variations and serves to obtain photopic response topographies.

Technical issues in electrodiagnostic recording

Electroretinogram (ERG) and visual-evoked potentials (VEPs) are used in veterinary ophthalmology to assess the functional integrity of the retina and the central visual pathway. The interpretation of altered electrophysiologic potentials in diseases can be of great diagnostic value, although it is important to be aware of technical factors and the limitations of these techniques which may result in over-interpretation and misinterpretation of the recordings, such that they are similar to those found in disease-related electrophysiologic changes. The recorded potentials represent the differences in voltage between the active and reference electrodes. The ground electrode serves as zero. A differential or instrumentation amplifier selectively amplifies signals of interest while rejecting noise. Differences between inputs are amplified, whereas common signals are rejected in a process called common mode rejection (CMR). In order for CMR to be most effective in reducing noise, the electrode impedances should be balanced. Filters are part of the differential amplifier as they remove unwanted noise of a certain frequency. The frequency bandwidth, or passband, is the range of frequencies between low- and high-frequency filter settings that are not filtered out. Major sources of noise that cause interpretation artifacts are power lines, amplifier noise, physiologic activity, electrochemical electrode noise and circular grounds. Noise reduction is achieved with high amplifier input impedance, balanced electrode impedances, CMR, filters and signal averaging. Maintaining electrodes in good condition, achieving proper contact between electrode and animal, and keeping electrode leads short aid in achieving noise reduction.

[Diagnostic techniques described in the study of Duchenne/Becker muscular dystrophy]

INTRODUCTION

Duchenne/Becker muscular dystrophy (DMD/B) is one of the commonest myopathies, with an incidence of 1/3,500 male live births. It is characterized by the slow degeneration of muscle fibres, so that the patient has become an invalid by the age of 10 years, followed by death from respiratory or cardiac failure. It has a sex linked recessive mode of inheritance.

DEVELOPMENT

The gene causing this disorder is the DMD gene and is found on the short arm of the X chromosome. The commonest mutations of this gene are deletions. Many molecular techniques for study of the disorder have been developed over the years. These include the Southern Blot, polymerase chain reaction (PCR), use of the Short Tandem Repeat (STR), polymorphic length restriction fragments (RFLP), Western Blot for the study of the protein and others.

CONCLUSIONS

In this paper we review the diagnostic tests most widely used in this disease. These have permitted improved study of the various families affected and thus improved the quality of life of the families at risk.

Electroretinogram contact lens electrode with tri-color light-emitting diode

PURPOSE

This study was performed to evaluate a new electroretinogram (ERG) contact lens electrode containing four light-emitting diodes (LEDs) that are used for both stimulus and background light.

METHODS

The luminance of each LED could be changed independently and used as stimulus light. Red, blue, bright white, and flickering ERGs were recorded in 12 normal subjects and two patients with progressive cone dystrophy. The long-duration light stimuli separated the on- and off-responses of the ERG. This equipment is not according to the ISCEV standard.

RESULTS

The tri-color LED electrode contact lens can efficiently produce and record ERG responses. Off-responses were recordable separately from on-responses by lengthening the stimulus duration.

CONCLUSION

This combined stimulus-electrode system is compact and portable. Combined with the portable amplifier and the recorder, the ERGs can be recorded easily in an operating room, at patients' bedside, and in remote locations away from clinics and hospitals.

Evaluation of the LKC stimulator for focal ERG testing

Numerous studies have demonstrated the ability of focal ERGs to diagnose abnormally functioning maculae in the absence of funduscopic and angiographic signs, as well as to confirm diagnoses of clinically suspected macular disease. We present normative data on the second commercially available focal ERG stimulator (FCS-500, LKC Technologies), which may be added to the standard full field ERG systems currently used in many laboratories. The stimulator uses a monocular indirect ophthalmoscope to present a 5 degrees white stimulus flickering at 31.25 Hz in a 20 degrees background field. We have established a range of normal amplitudes (747-3000 nV) and implicit times (30.5-37.5 ms) for the instrument based on tests of 45 eyes of 45 normal patients. To confirm the validity of this test for diagnosis of ocular dysfunction we compared these normals to 46 eyes of 46 patients with macular disease and decreased acuity, and to 49 eyes of 49 patients with retinitis pigmentosa. Using Focal ERG amplitude alone, we found overall accuracy of 85% in diagnosing macular disease associated with decreased acuity. These findings confirm the validity and efficacy of the system we have evaluated.

The electroretinogram and visual evoked potential of freely moving rats

The vascularised rat retina could be one of the most useful experimental objects in visual neuroscience to understand human visual physiological and pathological processes. We report here on a new method of implantation for studying the visual system of freely moving rats that provides a rat model for simultaneous recording at corneal and cortical level and is stable enough to record for months. We implanted light emitting diodes onto the skull behind the eyeball to stimulate the eye with flashes and to light adapt the retina with constant light levels. A multistrand, stainless steel, flexible fine wire electrode placed on the eyeball was used for electroretinogram recording and screw electrodes (left/right visual and parietal cortical) were used to record the visual evoked potential and the electroencephalogram. In the present report we focus on the new method of implantation for recording the corneal flash electroretinogram of normal, freely moving rats simultaneously with the visual evoked cortical potential showing examples in various visual experiments. We also introduce a program for retinogram and visual evoked potential analysis, which defines various measures (latencies, areas, amplitudes, and durations) and draw attention to the benefits of this method for those involved in visual, functional genomic, pharmacological, and human ophthalmologic research.

The pattern electroretinogram (PERG) with contralateral corneal reference

The pattern electroretinogram (PERG) is a sensitive test for investigation of the proximal retina. For monocular recording, the contralateral corneal reference (CCR) electrode position has been suggested as a possible alternative to the conventional ipsilateral temporal reference (ITR). We therefore compared the effect of these electrode positions on 26 subjects (median age 45.5 years, IQR 24.5-61.5). The signals were recorded monocularly with DTL nylon fibre electrodes. The visual stimuli were high contrast 19' black-white checkerboard patterns, reversing 4 times/s. PERG responses obtained from the CCR gave larger amplitudes and the increase in amplitude was statistically significant (P < 0.001). Because the CCR signal is larger, new normative ranges must be established to avoid false negative results.