Frequently Asked Questions |
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1. Does the Multifocal Imager 3Gen TM work with all monitors? 2. Which standards is the Multifocal Imager designed to comply with? 3. Why do I need to calibrate the scan delay with a new stimulus? 4. How easy is the device to setup? 5. Why do you recommend an 8 minute run for 61 element multi focal erg? 6. I’m receiving a peak at 50/60 Hz in the Fourier plot and the data is garbage, what is the likely cause? 7. Why is it important to create a library of site specific controls? 8. What do the traces of typical eye dysfunctions look like? 9. Should vision be corrected or uncorrected when carrying out multifocal electroretinography? 10. How can I limit interference with my results? 11. Which electrodes do you recommend be used with the system 12. Why is it important to exfoliate the electrode contact areas? 13. Why does dilation improve MFerg results? 14. When I carry out a VEP the system is crashing before I can collect any data? 1. Does the Multifocal Imager 3Gen TM work with all monitors? Multifocal Imager 3Gen TM will work with the majority of stimuli currently used. However, please contact Kelvin Vision to get a stimulus recommendation for optimised performance. Return to top of page 2. Which standards is the Multifocal Imager designed to comply with? Multifocal Imager 3Gen TM is designed to be compliant with ISCEV guidelines for multifocal electroretinography. http://www.iscev.org/standards/pdfs/mfERGStandardwFigs6-15-07.pdf Multifocal Imager 3Gen TM is a CE marked product and has been developed under ISO 13485. Return to top of page 3. Why do I need to calibrate the scan delay with a new stimulus? Stimulus screens have different time delays associated with them. The delay is the difference in time between when a screen is told to flash by the software and when it actually flashes. For optimised results it is recommended that you calibrate this scan delay when using a new stimulus for the first time. Return to top of page 4. How easy is the device to setup? The device comes with simple step by step instructions for setup. It is small and portable and should easily fit into most clinical environments. Return to top of page 5. Why do you recommend an 8 minute run for 61 element multi focal erg? This is suggested to give a sweet-spot in the trade off between spatial resolution, signal to noise ratio and test duration. With multifocal ERG a trade off exists between the following factors; signal to noise ratio, resolution, test duration, no. of stimulus elements and type of electrodes used. Decreasing the size (increasing the number for a fixed stimulus field size) of the stimulus elements and decreasing the duration of the recording will decrease the SNR of the responses. While decreasing the number (increasing the size) of elements will increase the SNR, it will decrease the spatial resolution of the test. When using the Multifocal Imager 3Gen TM with DTL type electrodes we suggest a run time of 8 Minutes (15 bit m-sequence) when using a 61 element display. Return to top of page 6. I’m receiving a peak at 50/60 Hz in the Fourier plot and the data is garbage, what is the likely cause? Poor electrode contacts, poor grounding or ambient sources of noise can cause line current (50 to 60 Hz) or CRT monitor (75Hz). The noise is easy to spot in the Fourier plot present during recording. The solution is to adjust or change the electrodes to give better contact, grounding and/or electrical shielding. Return to top of page 7. Why is it important to create a library of site specific controls? Each clinic must develop its own normative data. Variations in recording equipment and parameters make the use of data from other sources inappropriate. Because electrophysiological data are not necessarily described by a normal distribution, laboratories should report the median value rather than the mean, and determine 5% and 95% values as boundaries of normality. The mfERG, like the full-field ERG, is somewhat smaller in amplitude in older individuals and in those with highly myopic eyes. Although these effects are generally not large, they can be important in the evaluation of some patients. In any case, age-adjusted normative data is recommended. Return to top of page 8. What do the traces of typical eye dysfunctions look like?
9. Should vision be corrected or uncorrected when carrying out multifocal electroretinography? Although there is some evidence that the mfERG is unaffected by moderate blurring of the retinal image in healthy individuals, ISCEV recommend refraction for optimal acuity. Lenses can be placed in a holder positioned in front of the eye. The viewing distance must be adjusted to compensate for the relative magnification of the stimulus. Also care must be taken to avoid blocking the view of the stimulus screen by the rim of the lens or the lens holder and thus creating an apparent scotoma. Return to top of page 10. How can I limit interference with my results? Ensure that there is sufficient grounding and shielding from sources of electromagnetic interference. Return to top of page 11. Which electrodes do you recommend be used with the system? DTL electrodes are recommended for their: - Patient Acceptance - Ease of Use - Unaltered optical performance - Disposibility - Difficulty to ‘blink out’ DTL Plus Electrode TM Single use Corneal Electrode Manufactured by Diagnosys LLC: Re-order - D141 These devices are a Single use/non sterile product These electrodes are classified BF applied parts for the purpose of EN 60601-1:2006 Numerous studies have compared electrode quality for conventional electrophysiology and the results from these studies are also relevant to mfERG recording. An extensive review of ERG electrodes is provided in a paper by Coupland (1991). This paper is reproduced in Principles and Practice of Clinical Electrophysiology and Vision (John Heckenlively and Geoffrey Arden) Dawson – Trick – Litzkow (DTL) electrodes are low mass silver impregnated microfiber corneal electrodes. The low mass conductive thread makes contact with the tear film of the eye and is electrically connected using an insulated wire that is often taped to the cheek. The electrode is placed\dropped into the lower fornix. b amplitudes tend to be lower than the Burian – Allan electrodes produced but the electrodes are well tolerated by children and adults even with Keratitis. As they do not obscure the optics of the eye they are superior for recording pattern ERG and mfERG. DTL electrodes are not easily blinked out of the eye compared with GFE. “DTL electrodes provide robust and reproducible ERG recordings compared with corneal contact lenses and GFE’s for flash ERG, pattern ERG and multifocal ERG.”
- Stuart G. Coupland
Return to top of page12. Why is it important to exfoliate the electrode contact areas? Exfoliation is important as the outer most layer of dead skin cells offers the highest resistance of any of the skin layers due to low moisture\electrolyte concentration. As such to get a good electrode contact the contact area should be exfoliated. Return to top of page 13. Why does dilation improve mfERG results? By increasing the amount of light entering the eye by dilating the pupil the electrical responses from the eye are increased, making them more easily detectable. Return to top of page 14. From time to time the software has crashed when sending a sequence to the palette sequencer when performing The problem has been identified as to do with the screen used to setup an investigation for the VEP. See below.
If However 'Continue' in the top tool bar is selected, nothing visible happens. You then have to press 'Save and Continue' under where it says right eye. At first it looks as if everything is going through OK. But then the software crashes. This issue will be resolved in software update build 256. |
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