The ffERG/Flash Plus Photopic Negative Response vision test from Diopsys provides eyecare professionals with objective, functional information on the health of retinal ganglion cells (RGCs). “Retinal ganglion cells, the cells that are damaged primarily by glaucoma, don’t regenerate after they die off,” says Alberto González García, MD, chief medical officer for Diopsys. “Current structural tests, such as optical coherence tomography [OCT], show physicians if the cells are present [alive] or not [dead], but they don’t provide information on whether living cells work properly.”
In addition, OCT or perimetry testing to confirm early damage requires multiple tests over a 12-month to 24-month period. “Waiting for such confirmation results in the irreversible loss of tens of thousands of RGCs,” says William Eric Sponsel, MD, FACS, director of the glaucoma service at WESMDPA in San Antonio, Texas.
The Diopsys test measures how well RGCs function. “If they are under stress due to intraocular pressure, their electroretinography [ERG] response will be diminished,” says Dr. Gonzalez. “Physicians can start therapy at this early stage, taking the stress off RGCs and making them healthy again. If physicians intervene before cells die, they can help prevent vision loss from the disease.”
Diopsys also provides another test of RGC function called pattern ERG (PERG). PERG has been shown to detect RGC dysfunction up to 8 years before changes in retinal nerve fiber layer (RNFL) thickness occur as shown on OCT.
“Both the PERG and ffERG with photopic negative response [PhNR] tests are clinically valuable, but with the new Diopsys ffERG/Flash Plus PhNR test, patients don’t need to be refracted and may be tested in a lit room,” says Dr. Gonzalez. Fixation on the stimulus is also less important because it does not affect the amount of light being presented to the eye.
“PhNR opens up a new capability for active disease confirmation before cells die,” Dr. Sponsel says. “This is an important advancement, because like any other neuron in the central nervous system, RGCs can’t be regenerated. PhNR allows me to decide whether to be more aggressive or hold back on surgical intervention, without incurring avoidable permanent neural loss as a necessary part of the decision process.”
How It Works
The test is designed to evaluate the early stages of disease, such as ocular hypertension or preperimetric glaucoma. “It should be used to initially verify and subsequently manage glaucoma or any other disease affecting the metabolic integrity of the retina’s inner layers,” Dr. Sponsel says.
To begin the test, the technician places 3 sensors on the patient — 1 beneath each eye at the lower lash line and 1 on the forehead, Dr. Gonzalez says. Then, the patient holds a handheld device (a mini Ganzfeld dome stimulator) over the eye to be tested.
Patients open their eyes and look into the dome while being tested. They should avoid excessive blinking.
The visual stimulus presented within the stimulator provokes a response from RGCs that is recorded and analyzed by the Diopsys testing system. A report is generated for evaluation.
“The PhNR test is completely objective,” Dr. Gonzalez says. Patients don’t have to verbally respond or push a button for the physician to get information. The extra information on RGC function can help physicians improve their clinical evaluation, potentially leading to an earlier diagnosis or indicating that the patient doesn’t have the disease yet.”
Adds Dr. Sponsel, “Because of the spatial intimacy of the testing setup and constant uniformity of the alternating bright red and blue stimuli, attaining standardized testing outcomes is reasonably assured even with compromised patient compliance.”
Ease of Use
The test is user friendly for physicians and technicians. “Diopsys’ devices and vision tests easily fit within a practice’s testing line; technicians can run the test with basic training,” says Dr. Gonzalez. “Test reports follow standard forms of clinical reporting.”
Dr. Sponsel says the software is intuitive and user friendly; the photopic negative response test is straightforward for technicians to perform. The system’s software creates standardized printouts similar to those generated by other clinical technologies that patients are accustomed to seeing, making it easy to interpret findings and explain their relevance to patients.
Benefits for Patients
One of the most challenging parts of glaucoma management is early diagnosis when current available tests are often not confirmatory or they contradict one another. “Suspect patients have problems and histories that put them at risk to develop the disease, but identifying who will actually develop the disease is difficult,” Dr. Gonzalez says. “Most of the time the physician will wait until structural changes occur (ie, cell death) to confirm a diagnosis, but at that point vision loss has already begun. The ffERG/Flash Plus PhNR can help physicians increase their level of confidence in the diagnosis even before an obvious form of structural damage is present.”
Furthermore, numerous practices report that patients find the test to be pleasant and not stressful, especially when compared to testing such as the visual field test, Dr. Gonzalez says.
PhNR can noninvasively help distinguish eyes at high risk that require maximal intervention from eyes that should be observed. “The simplicity of its standardized results allow patients to participate in properly informed decision making about treatment priorities,” Dr. Sponsel says.
“PhNR is an objective and technician-friendly test that is easier on the patient and technician than many other standard testing methodologies,” Dr. Sponsel concludes. “The test can provide an immediate answer to the important clinical question: ‘Is this patient’s eye at risk of glaucomatous progression, or is it likely to remain stable under our current treatment regimen?’ Such a quick, reliable, and fundamentally objective test can greatly improve the quality and efficiency of care.” GP