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Diopsys Insights

Straightforward and Actionable Vision Test Results: Diopsys® ffERG/Flicker ERG Reports


INTRODUCTION:

One of the perceived barriers associated with visual electrophysiology is that testing is complicated, and interpretation of the results requires the input of a neurophysiologist. While this may be true of older devices, the electrophysiology testing on Diopsys platforms are specifically designed to be much friendlier – both for the patient and for the clinician.

There are a few key parameters on the Diopsys® ffERG/Flicker reports that clinicians need to understand for this testing to provide actionable information for clinical decision making. Once understood, these vision test results will improve the ability to understand the health of the retina for enhanced patient management.


What is ffERG?

Full Field Electroretinography (ffERG) tests are the only diagnostic/prognostic tests used in eye care that provide objective information about the function of the retina. Results are a measurement of the summed electrical responses from the entire retina elicited by a flash stimulus delivered in a ganzfeld dome.

Flicker ERG is a type of ffERG test that uses a flash stimulus occurring at a fast rate (i.e. “flickering”) used to record the function of cone and bipolar cells.

Diopsys devices use a handheld mini-ganzfeld held over the eye to stimulate retinal cells. The tests measure how much energy is created at the retina and the timing of the response. Results help improve the clinician’s ability to track disease progression and response to treatment.

There are two types of flicker ERG testing available from Diopsys: multi-luminance flicker (ML-ffERG) and fixed luminance flicker (FL-ffERG).

  • ML-ffERG uses six increasing luminance levels (dim to bright).
  • FL-ffERG uses a fixed luminance level.

Both types of ffERG can be used in the presence of media opacities.

Breaking it Down – What is on the Report?

The reports generated after the tests concisely present the most important information needed for medical decision-making (Figures 1 and 2). The data from ffERG is often crucial for making informed decisions about treatment, diagnosis, and prognosis.

Below is a breakdown of the items that appear on Diopsys ffERG reports:

Multi-Luminance Flicker (ML-ffERG)
There are five key items on the report to know (click interactive icons):

 
  1. Signal Quality Indicator – Green, yellow, or red sensors indicate the quality of the connection to the patient through the electrodes (note: this is an index of proper test preparation and not the placement of the electrodes).
  2. Magnitude Graph – Vertical axis indicates the strength of the patient’s response in microvolts at each luminance level, with a normal response indicated by increasing strength at each luminance levels. Variance bars indicate the variance in magnitude for each luminance level, with shorter bars suggesting a more consistent response.
  3. Phase Graph – Vertical axis indicates the timing of the response in degrees at each luminance level, with a normal response indicated by an increase in phase at each luminance level. Variance bars indicate the variance in phase for each luminance level, with shorter bars suggesting a more consistent response.
  4. Mag/Phase Plot – An overlay of the Magnitude and Phase for each of the six luminance levels tested for both eyes, which becomes useful for detecting asymmetry. A “normal” finding in healthy eyes is depicted as closely tracked lines with plotted lines curving toward the lower right quadrant.
  5. Data Table – The two most important data points listed: (1) “Area Ratio” indicates the area value relative to the average reference response in healthy eyes; and (2) “Asymmetry (%)” compares responses from each eye. The Area Ratio and Asymmetry data is compared to documented reference ranges and then color-coded.

Fixed Luminance Flicker (FL-ffERG)
There are four key items on the report to know (click interactive icons):

 
  1. Signal Quality Indicator – Green, yellow, or red sensors indicate the quality of the connection to the patient through the electrodes (note: this is an index of proper test preparation and not the placement of the electrodes).
  2. Magnitude Graph – Vertical axis indicates the magnitude of the response. Most responses should present as two relatively equally spaced peaks and larger magnitude values can be an indication of good function.
  3. Mag/Phase Plot – Magnitude of each response is represented by the length of each blue line and the Phase of each response is represented by the degree, or angle of each blue line from the center.
  4. Data Table – (1) “Magnitude (uV)” represents the strength of the signal; (2) Phase(o)” is related to the timing of the patient’s response to the visual stimulus; (3) “Asymmetry (%)” compares responses from each eye; (4) “Magnitude Variance Ratio” and “Phase Variance Ratio” represent the variability of the Magnitude and Phase Variances of a reference group of healthy subjects; a value equal to or greater than 1.00 indicates that the variance of the patient’s response was equal to or better than the average variance from the reference group.

How I Use The Reports In My Clinic

The ffERG reports can be very helpful for following retinal disease and treatment success for things like diabetic retinopathy and retinal vein occlusions. In my practice, which is primarily anterior segment focused, most of my patients with concomitant retinal disease are managed and followed by retina specialists. 

I rely on the ffERG test results when evaluating patients for cataract surgery. It’s actually quite common that I have patients sent to me with advanced cataracts and questionable retinal status. In these advanced cataract patients, typical measures of potential visual acuity and retinal health are not helpful and so it can be difficult to counsel both the patient and their family regarding the potential benefits of surgery. 

I can easily review an ffERG report with these patients and explain that the results provide an objective measurement of their retinal function. I discuss that the results are helpful in both determining which eye may have greater visual potential as well as setting realistic expectations for surgery.

While some cataract surgeons will not perform cataract surgery on a patient with a mature cataract, I will absolutely consider performing the surgery if I have their ffERG test results. 



CONCLUSION:

Diopsys® ffERG/Flicker results help eye care specialists understand their patients’ retinal health in a way no other test can. The objective information informs on how the retina is functioning, not just how it looks. The data is presented in a straightforward report that even patients can relate to during consultations.

Once doctors realize the valuable information provided by ffERG results, they won’t want to proceed without this data either.

This article represents the experiences and opinions of Richard Tipperman, MD. Physicians should make medical decisions based on the individual facts and history of each patient.

Topics: Flicker ERG

Modern Visual Electrophysiology

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As the world leader in modern visual electrophysiology, Diopsys, Inc. has done more than any other company to advance the use of ERG and VEP in the eye care practice. Read through our blog to gain valuable insights into the benefits and integration of this valuable technology.

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