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Multifocal ERG Quick Reference

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Multifocal ERG Quick Reference

Posted on Thursday August 27, 2020

Multi-Focal ERG: applies to all mfERG tests on LCD monitors

Explanation for patients:
This test is similar to an EKG that tests parts of your visual system instead of your heart. We stimulate your visual system using patterns of light and then measure the electrical response in the eyes. The size, shape, and speed of these responses measures the health of the visual system. This test involves putting electrode sensors on the forehead and eyes and measuring the response as you look at flashing patterns of black and white.

Materials:

  • Eye drops: a) Dilating, b) Corneal anesthetic, c) Artificial tears
  • Electrodes: a) 2 DTL Plus® electrodes, b) 1 set of extender cables, c) 3 gold cup or sticky pad electrodes
  • Alcohol pads
  • Skin Prep: skin scrub pads or Nu Prep® exfoliating scrub
  • Ten 20® conductive paste
  • 3 strips of medical tape (if using gold cups)
Figure 1: Closeup of patient setup
Figure 2: DTL placement

Patient preparation:

  • Dilate the patient’s eyes?:YES
  • Vision must be corrected to 20/30 or better. Additionally: we recommend using a +3 diopter correction.
  • Scrub forehead and temples where electrode will be placed with Skin Prep; alcohol wipe as needed.
  • Place skin electrodes on the forehead and temples (Figure 1). If using gold cups first over fill each with Ten 20 conductive paste, also place conductive paste on the scalp, position the gold cup on
    scalp and tape in place.
  • Place a drop of corneal anesthetic in each eye, then place the DTL electrodes (see Figure 2). The DTL small sticky pad goes next to the nasal canthus; the larger pad next to the temporal canthus.
    The DTL fiber should drape across the lower lid & should NOT fall into the conjunctival sac.
  • Help patient remain relaxed during test. Dim room lights & occlude eye not being tested.

Amplifier setup diagram:

  • The FOREHEAD should be plugged into input [Cz/Gnd].
  • The patient’s RIGHT EYE should be plugged into the [Right Eye +] input.
  • The RIGHT TEMPLE should be plugged into the [Right Eye –] input.
  • The LEFT EYE should be plugged into the [Left Eye +]  input.
  • The LEFT TEMPLE should be plugged into the [Left Eye –]   input.

Figure 3: Amplifier connections

Pre-test checks:

  1. Plug the patient into the amplifier.  Press the Imped. button to check connection quality.
    • Impedance Color Action required
      <5k Ohm None
      >5k and <10k Ohm ???? Try to improve connection if possible
      >10k Ohm May require electrode replacement and/or skin re-preparation
  2. Press the Preview button to monitor the signal and ensure noise levels are acceptable.

Testing procedure:

Step 1:  Place patient in front of monitor and on the chin rest.  First, adjust the height of the chinrest so that the patient is positioned in the center of the monitor, both up/down and left/right.  The patient should be able to clearly see the fixation X in the center of the monitor. For patients with poor central vision, it may be necessary to enlarge the fixation X.  For these patients, press the Stimulator button and pull the Fix Size slider up to adjust size and width of the central red cross lines.  Instruct these patients to fixate where those lines would intersect.  

Step 2: Explain the test procedure to the patient.
“We are going to test each eye’s response to patterns of light.  The test will take about 4-7 minutes.  You will have a break every 30 seconds to blink and relax.  Try to minimize blinking during the test when the hexagons are flashing.  All you need to do is relax, try not to blink, and fixate on the cross in the center of the screen.”

Notes:

  1. Room lights should be dimmed if possible.
  2. Pause the test as needed, if the patient needs a break.
  3. Use artificial tears as necessary during the test to keep patient eyes as relaxed as possible.
  4. Typically test both eyes at same time.  You may test 1 eye at a time where needed (e.g. nystagmus)
  5. Very important: Ensure the patient can clearly see the fixation point in the center of the monitor.
  6. Important: Ensure patient eye glass rims or trial lens rims are not blocking any of the mfERG pattern.

Step 3:   Begin the test by pressing    in the lower left corner.  After each 30 second test segment allow the patient to relax and blink.  When ready press   again to continue the test until 100% complete.  Follow instructions of the test from the software as you proceed through each of the steps.

Step 4: Save by pressing Exit and saving the test when prompted. Re-open the test.  Press the Print button to bring up the print preview, select the correct Print Template and then press Print again to print. 

Note: if you accidentally elect not to save, you will be asked to confirm.  If you confirm you wish to discard the test in error, contact diagnosys to retrieve the test data