Clinical display of mfERG data

Many mfERG displays show normal responses that are larger at the center than peripherally, and the typical linear display of signals is inaccurate with respect to the retinal location of the signals. Printouts do not always indicate retinal or field view, they sometimes emphasize 3-D topographic plots which are not always representative of physiologic signals, and they show ring response densities which are different in every ring and hard to interpret without norms. These problems limit the clinical usefulness of the mfERG and limit communication in the literature. We share our Stanford Display to illustrate possible solutions to these problems.

We have changed the scaling factor for our mfERG unit to produce a trace array with near equal signals everywhere. We display responses is a spatially scaled array, in a retinal view, so that signals appear in their correct anatomic locations relative to a fundus image. The 3-D display is minimized on the page of signal analysis, and we emphasize ring response averages rather than ring response densities.

The new scaling and trace array display greatly facilitate the analysis of retinal disease. Regions of loss are easily recognized in their fundus location. Ring ratios based upon response amplitudes all have a normal value of 1.0 which simplifies analysis. A case of early hydroxychloroquine retinopathy demonstrates the use of this Stanford display.

Recognition of these recording and display options may help mfERG users to maximize the value of the test. Proper scaling of the mfERG stimulus array facilitates localization of retinal disease and simplifies ring response analysis. Different laboratories will have different priorities for signal analysis, but mfERG displays should always indicate the eccentricity of responses, and the use of a retina or field view.