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Diopsys Insights

The Reason This Ophthalmologist Uses Flicker ERG

Posted by Mitchell A. Jackson, M.D. on December 9, 2016 at 3:09 AM


All of us anterior segment surgeons have coached our patients through the cataract surgery procedure and what type of vision they can expect when fully healed. The potential for diagnosing an existing retinopathy in patients with mild cataracts prior to surgery is relatively high. But predicting retinopathies and setting the proper patient expectations become more difficult when a dense cataract prohibits me from getting a reliable OCT or fundus photo. So what do I tell these patients? 

Now I have a reliable, objective test of retinal function that I can perform pre-operatively to give me an idea of what's going on behind the cataract. Flicker ERG has helped me ensure that these patients are accurately prepared for the outcome of their surgery. 

Flicker ERG – Flash ERG – ffERG

Full field electroretinography (ffERG) testing provides objective information on the function of the entire retina, evoked by a flashing light from a Ganzfeld stimulus. Flicker ERG is a type of ffERG test where the light flashes very quickly at 30Hz or more. Because rod photoreceptor cells cannot follow such a fast stimulus, the cone response is isolated and measured. The biggest gain I get from flicker ERG testing is that I can measure cone function even through the presence of an opacity.

The Benefit

If a patient has a very dense cataract, such as mature and/or dense nuclear sclerotic cataracts, where we can’t see the macula or retina with an OCT and all we can do is a B scan to see if there is a tumor or hemorrhage, I’m not confident that patient’s post-op vision will be significantly improved. Even if the B-Scan is normal, it does not tell me if retinal function is normal. Identifying which IOL to use with these patients is also in question.

With flicker ERG vision testing, we can now actually determine cone function ahead of time in a very dense media opacity. In my practice, we usually run the flicker ERG test at our pre-op evaluation appointment or at their follow-up scheduling visit. I can then have a more decisive conversation with the patient about their potential for improved sight following surgery, and which lens may be best for them.

How it Works

The patient is brought to the testing room, and our technician preps the patient’s skin in the center of the forehead and underneath both eyelids with cleansing pads so that the sensors have good contact with the skin. The tech then places each sensor on the cleansed areas, and connects the wires to the device. The under-lid sensors developed by Diopsys make this process much more patient- and tech-friendly than you may remember from med school.

ffERG Patient Set-Up

After placing the three sensors, the patient is given a hand-held mini-Ganzfeld. I like to note that the lights are left on for this test, and eyes should not be dilated. The tech then runs the test while the patient holds the dome over their right eye, switching halfway through to test their left eye.


Managing my patient's expectations for cataract surgery is critical to the success of their perceived outcomes. I want my patient's to be happy with the care we provide them, and that means making sure they are informed of the likelihood of better post-operative vision. Having a test that allows me to be more accurate in setting those expectations means my patients are better educated and we can make the best decision for their ocular health.

- Mitchell A. Jackson, M.D.
Jacksoneye, Lake Villa, IL

The Diopsys® NOVA™ is an electrophysiology device that generates photic stimuli, and records, processes, and analyzes the resultant signals to provide information about the visual system. This article represents the experiences and opinions of Dr. Mitchell Jackson. Physicians should make medical decisions based on the individual facts and history of each patient.

Would you like to see how a Diopsys® ffERG test is run?

 Watch ffERG Video

Topics: Flicker ERG

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