Multifocal ERG recording with simultaneous fundus monitoring using a confocal scanning laser ophthalmoscope

Multifocal Electroretinography in the Presence of Temporal and Spatial Correlations and Eye Movements

Releasing patients from the fixation task, and permitting them to view natural stimuli such as movies, would provide increased comfort, and potentially additional signs of retinal function, when recording multifocal electroretinograms (mfERGs). Techniques must be developed to handle the difficulties that arise from these alternative stimulation strategies. Multifocal stimuli were presented to volunteer human subjects with and without fixation. Retinocentric analyses were performed to deal with shifts of the stimulus across the retina in the presence of eye movements. Artificial scotomas that moved with the eyes to simulate local retinal defects were presented to assess whether such defects might be detectable in the presence of eye movements. Temporal and spatial correlations in the stimulus can be discounted, permitting retinal kernels to be measured in response to natural stimuli. Responses to temporally natural stimuli tend to have slightly stronger amplitudes because of the presence of low temporal frequencies in these stimuli. The effects of eye movement artifacts can be reduced, permitting similar kernels to be obtained in the absence and presence of eye movements. Convergence to stable kernels took slightly longer in the presence of temporal correlations or eye movements. Artificial scotomas can be localized with these methods. It may be possible to perform multifocal ERG recordings in the clinic using more flexible, natural techniques. However, work is needed to achieve results comparable to those routinely obtained with conventional methods.

Optoelectrophysiological stimulation of the human eye using fundus-controlled silent substitution technique

We design, characterize, and apply a novel optoelectrophysiological setup for a fundus-controlled silent substitution technique that accounts for interindividual variability in retina morphology and simultaneously monitors the stimulation site under investigation. We connect a digital color liquid crystal on silicon projector, an electron-multiplying imager, and a light-emitting diode to a fundus camera. The temporal and spatial characterization reveal a maximal contrast loss of 7% for the highest stimulation frequency (30 Hz) and maximum cutoff spatial frequencies of ∼120 cycles∕deg. Two silent substitution flash sequences are applied to modulate selective activity in the short-wavelength-sensitive cone (S-cone) and combined long- and middle-wavelength-sensitive cone (LM-cone) pathways. Simultaneously, the visual evoked potentials are recorded. The data are compared to the grand average responses from a previous study that employed standard computer-screen presentation and showed very good latency matches. All the volunteers in the present examination exhibit differences between the S-cone and LM-cone evoked potentials (parameters mean values: peak-to-peak amplitude, N1 latency, and P1 latency for S-cone∕LM-cone responses: 8 μV∕15 μV, 113 ms∕89 ms, 170 ms∕143 ms). We demonstrate that the developed optoelectrophysiological setup simultaneously provides imaging, functional stimulation, and electrophysiological investigation of the retina.

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.

RPE transplantation and its role in retinal disease

Retinal pigment epithelial (RPE) transplantation aims to restore the subretinal anatomy and re-establish the critical interaction between the RPE and the photoreceptor, which is fundamental to sight. The field has developed over the past 20 years with advances coming from a large body of animal work and more recently a considerable number of human trials. Enormous progress has been made with the potential for at least partial restoration of visual function in both animal and human clinical work. Diseases that have been treated with RPE transplantation demonstrating partial reversal of vision loss include primary RPE dystrophies such as the merTK dystrophy in the Royal College of Surgeons (RCS) rat and in humans, photoreceptor dystrophies as well as complex retinal diseases such as atrophic and neovascular age-related macular degeneration (AMD). Unfortunately, in the human trials the visual recovery has been limited at best and full visual recovery has not been demonstrated. Autologous full-thickness transplants have been used most commonly and effectively in human disease but the search for a cell source to replace autologous RPE such as embryonic stem cells, marrow-derived stem cells, umbilical cord-derived cells as well as immortalised cell lines continues. The combination of cell transplantation with other modalities of treatment such as gene transfer remains an exciting future prospect. RPE transplantation has already been shown to be capable of restoring the subretinal anatomy and improving photoreceptor function in a variety of retinal diseases. In the near future, refinements of current techniques are likely to allow RPE transplantation to enter the mainstream of retinal therapy at a time when the treatment of previously blinding retinal diseases is finally becoming a reality.

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.

Age-related macular disease: how to assess the retina using scanning laser techniques?

Age-related macular disease (AMD) is the leading cause of legal blindness among the elderly in Western nations. The magnitude of the problem will undoubtedly grow, as age is a significant risk factor and the number of people aged 65 and over is projected to increase. The most frequent cause of severe visual loss associated with AMD is irreversible degeneration of the overlying neurosensory retina, caused by the growth of choroidal neovascularization or, alternatively, the development of geographic atrophy of the retinal pigment epithelium. Today, we are able to image the human retina in vivo. Recently developed imaging techniques provide better assessment of retinal pathology than conventional ophthalmoscopy alone. This overview presents the most recent devices available for retinal imaging, which mainly exploit laser technology such as scanning laser ophthalmoscopy. Its basic principles, as well as its characteristics for imaging and functional assessment of the retina, are described. Lastly, potential benefits for clinical routine, rehabilitation strategies in AMD, and future research aspects are discussed.

An Instrument Capable of Grading Visual Function: Results from Patients with Retinitis Pigmentosa

There was no device to grade visual function in patients with retinitis pigmentosa (RP). We have therefore developed an instrument capable of measuring and quantifying the visual capabilities, and here present the results from patients with RP. In total, 118 eyes of 59 patients, 26 men and 33 women, with RP were studied. Seven eyes had hand movement (HM) and eight had light perception (LP) vision, and the others had better visual acuity. The Low Vision Evaluator (LoVE) consists of a pair of goggles with white, light-emitting diodes as the stimulus, a control box, an on-off button to signal the detection of the stimulus, and a printer for permanent records. There are 15 luminance levels of stimuli (combination of 5 intensities and 3 durations). The stimuli are delivered in a random sequence with an audio signal presented 0.3 seconds prior to the light stimulus. Each eye was tested separately, and each stimulus magnitude (intensity x duration) was presented 3 times for a total of 27 stimuli per eye. With 6 catch trials (audio signal without a light stimulus), a total of 60 trials were examined in a full examination. The conventional visual acuity and kinetic visual fields were determined. 59 patients had different visual acuities that ranged from no light perception (NLP) to 1.5 vision, and visual field sizes that ranged from 0.0001 to 3.96 steradians. The visual acuity and visual field size were significantly correlated with the LoVE score (r=0.58 and 0.64, respectively; p<0.01). These results indicate that the LoVE is capable of grading the visual function of RP patients with various visual acuities and visual fields. The testing procedures are simple for the patient and examiner, and this instrument can be used to assess the effectiveness of medical and surgical therapy.