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

[Electrophysiological parameters of the retina in idiopathic macular hole]

AIM

To investigate the nature and range of electrophysiological disturbances in idiopathic macular hole (IMH) and establish their relationship with structural parameters of the retina.

MATERIAL AND METHODS

The study included 249 patients (280 eyes) with IMH. All of them underwent ganzfeld and multifocal electroretinography (ERG), optical coherence tomography, and evaluation of retinal electrical sensitivity and analyzer lability. The results were then compared to those of non-IMH patients (196 paired eyes) and controls (25 people, 49 eyes).

RESULTS

Multifocal ERG findings prove that IMH is always associated with significant changes in bioelectrical potential of the central retina. In 62% of cases its decreased density and extended latency were registered in not only the fovea, but also the para- and perifovea. In 8% of cases the changes involved everything within a 30-degree area of the central retina. In 30% of cases the maximum bioelectric potential was found to have shifted from the centre to para- and perifovea, its amplitude and density being supernormal for these regions (shift phenomenon). A weak correlation between electrophysiological parameters and retinal thickness around the hole has been also established.

CONCLUSION

Of all methods used to assess retinal function in IMH, multifocal ERG is the most informative. In 100% of cases foveal biopotential is sharply reduced in density and disfigured. In 70% of cases these changes spread outside the fovea.

Multifocal electroretinography

Multifocal electroretinography (mfERG) provides functional and objective evidence of retinal dysfunction. We have found mfERG to be especially useful in the management of occult outer retinopathy and Stargardt's disease.

Simultaneous structural and functional imaging of the macula using combined optical coherence tomography ophthalmoscope and multifocal electroretinogram

Multimodal imaging (MMI) is a new imaging technique that combines an electrophysiological test (multifocal electroretinogram) with an optical coherence tomography ophthalmoscope. MMI allows the two technologies to operate simultaneously yet independently to provide accurate correlation of macular structure and function at multiple sites. Preliminary work with MMI in patients with macular holes showed that functional deficits existed beyond the geographical area of structural alterations and that macular hole size did not always correlate with the severity of functional loss. Functional information may therefore be important when assessing prognosis in these patients. We envisage that MMI may prove a useful new tool in the assessment of many macular pathologies.

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.

Effects of unsteady fixation on multifocal electroretinogram (mfERG)

PURPOSE

To investigate the effect of unsteady fixation on the multifocal electroretinogram (mfERG) measurement in normal subjects.

METHODS

The mfERGs of 20 subjects with normal vision (mean age=23.5 years) were recorded with different levels of voluntary eye movements made to mimic unsteady fixation. Subjects were required to move their fixation regularly every 2 s between the center and the ends of a fixation cross, so that 51.2% of the time fixation was at the center and 12.2% of the time it was at each end of the fixation cross. Four different conditions were performed: central fixation (without voluntary eye movements) and with 2 degrees, 4 degrees and 6 degrees magnitude of unsteady fixation. First-order kernel mfERG findings are presented.

RESULTS

Analysis of the ring responses indicated that the central mfERG amplitude was most affected by unsteady fixation. There was significantly reduced amplitude for 4 degrees unsteady fixation and as expected, this reduction became larger with 6 degrees unstable fixation. However, there was no significant effect on the center hexagon amplitude for 2 degrees unsteady fixation. The amplitudes of the ring-2 responses were only affected in the 6 degrees unsteady fixation condition. No significant change in implicit time was found for any level of unsteady fixation.

CONCLUSION

These results suggest that mfERG amplitude is not substantially affected if fixation is maintained within the central stimulus hexagon. We conclude that, for patients with poor fixation, the accuracy of mfERG results may be difficult to interpret and the use of a fixation-monitoring system is desirable for ideal measurement. The depth of depression at the blind spot area may be another useful parameter to interpret the accuracy of mfERG results in patients with poor fixation.