Broadly speaking, uveitis is inflammation affecting the uveal tract, although management and prognosis for vision loss differs significantly according to what part of the eye is affected (i.e., anterior, posterior, intermediate, or panuveitis). Thus, prompt identification and localizing of inflammation is critically important, even though early indicators of active disease are often subtle and may not be apparent on clinical examination or on imaging.
For patients with uveitis and suspected retinal involvement, results from a flicker electroretinogram (flicker ERG) are extremely useful for making a diagnosis and monitoring disease activity. Clinicians can identify retinal dysfunction early then see functional improvement on the flicker ERG after the introduction of anti-inflammatory treatment with steroids or immunomodulatory therapy. An improvement in retinal function can indicate the plausibility of tapering the drug dosage.
Tracking Treatment Success with Flicker
One of the bedrock principles in managing uveitis is to get patients to steroid-free remission if at all possible, and to reduce use of systemic immunomodulatory therapy to the lowest effective dose. Reversing the loss of signal in the early stages of uveitis on repeat flicker ERG suggests that the stress to the retinal cells has been abated or removed, and in turn, that it may be possible to transition the patient to a long-term maintenance regimen. There is emerging evidence that in some patients, normalizing the flicker ERG in the early stages of uveitis can lead to long-term remission off therapy.
Detecting Uveitic Glaucoma with PERG and VEP
A second important application of electrodiagnostics in uveitis is to detect pre-perimetric glaucoma using pattern ERG (PERG) and visual evoked potential (VEP) testing. Uveitic glaucoma tends to be a much more aggressive entity than other glaucomas. Fortunately, changes on PERG and VEP are recognizable months to years earlier than other testing methods like OCT.
Early detection and initiation of proper treatment can lead to functional recovery shown on PERG and VEP results, which correlates with lower risk for permanent vision loss and improvement in other clinical parameters.
Access Leads to Expanding Indications
The most robust evidence for using electrodiagnostic testing in patients with uveitis is in birdshot chorioretinopathy. However, the same principles apply to any patient with uveitis and suspected retinal involvement. In addition, the availability of these tests for practicing clinicians is helping to discover new applications.
For instance, in our clinic, we have found that flicker ERG can be useful for identifying abnormalities in the fellow eye of a patient with apparent unilateral uveitis, which has allowed us to perform advanced imaging studies and identify areas of occult inflammation. We are still working to codify risk factors for when such testing is useful, but the point is, we never would have discovered this if we had to constantly refer patients out for testing.
It is our view that flicker ERG is already indispensable for patients with diabetes having multiple injections who have an epiretinal membrane, as OCT is often inconclusive to detect response to treatment. Again, the flicker ERG gives us confidence regarding the effectiveness of the intervention and tells us whether it is possible to extend the interval or suspend treatment.
The beautiful thing about having an office-based system is that it is inexpensive, the test is performed with results available the same day, and it is easy for the patient. Before we had access to this testing in the clinic, we were not doing electrodiagnostic testing enough. Now, we are doing it more and I am certain that we are going to find additional applications for the use of this technology.
Most ophthalmologists are likely already familiar with electrodiagnostics, at least in principle. It is well established that visual electrophysiology is the only kind of testing that provides objective information about the health of the cells along the visual pathway. There is now a long record of studies that have established the role of electrophysiology testing in a wide array of pathologies affecting the retina, macula, optic nerve, and other ocular structures.
The advent of office-based electrodiagnostics significantly changes how this testing can be used in the clinic, and yet we may only be scratching the surface in terms of its utility. As the gold standard for tracking treatment results, the use of flicker ERG in uveitis provides a good example of how testing can affect medical decisions, as well as how the role of testing can evolve in routine settings.
This article represents the experiences and opinions of William Ayliffe, FRCS, PHD. Physicians should make medical decisions based on the individual facts and history of each patient.