Mode of display
Trace arrays: It is essential to show the trace array when reporting mfERG results (see Fig.
3a, b). These arrays not only show topographic variations, but also demonstrate the quality of the records, which is important in judging the validity of any suspected variations from normal. Trace lengths of 100 ms or more should be used for these displays. (It is hard to detect interference from line frequency and/or kernel overlap in shorter trace lengths.).
Group averages: Arranging responses by groups can be a useful way to summarize the data. Concentric rings of traces, from the center outward, are most commonly used. Regions with fundus pathology can be averaged together if desired. Most laboratories report response density (Fig.
5a).
Three-dimensional plots: These should be used with caution and only when accompanied by trace arrays (see above). The 3-D plots (Fig.
3c, d), without accompanying trace arrays, can be misleading (see Appendix). Note that if fixation is steady and central, a clear depression due to the blindspot should be present and located in the appropriate place.
Measurements calibration marks: Calibration marks must accompany all traces or graphs. This will enable comparisons among patients or within a patient on sequential visits.
Measuring mfERG amplitude and timing: The N1 response amplitude is measured from the starting baseline to the base of the N1 trough; the P1 response amplitude is measured from the N1 trough to the P1 peak (see Fig.
2). The peak times (implicit times) of N1 and P1 are measured from the stimulus onset. Measurements of group averages should routinely include the N1 and P1 amplitudes and peak times.
Commercial software provides measures of the overall amplitude and timing of the mfERG traces. There are various procedures for measuring amplitude (e.g. trough-to-peak amplitude), latency (e.g. response shifting, response stretching, time to peak), or overall response waveform (e.g. scalar product, root-mean-square (RMS)). A description of these techniques is beyond the scope of these guidelines. However, it should be noted that when a template is needed (e.g. for scalar product measures), the template should be formed from age-similar control data obtained from that laboratory.
Color scales: The use of color scales is optional; care should be taken when reproducing color images on a gray scale as the luminance sequences may not be in the proper order.
Normal values
Each laboratory must develop its own normative data. Variations in recording equipment and parameters make the use of data from other sources inappropriate. Because electrophysiologic data are not necessarily described by a normal distribution, laboratories should report the median value rather than the mean, and determine boundaries of normality. The mfERG, like the full-field ERG, is somewhat smaller in amplitude in older individuals and in those with highly myopic eyes. Although these effects are generally not large, they can be important in the evaluation of some patients. In any case, age-adjusted normative data is recommended.
Reporting of artifacts and their resolution
Reports should indicate any problems with the recording such as movement, head tilt, poor refraction capability, poor fixation, etc. that might affect reliability and interpretation. Also, indicate explicitly any artifact reduction procedures or post-processing maneuvers used to prepare the data. This should include the type and number of artifact rejection steps, the spatial averaging with neighbors (noting the extent and number of iterations), and any other averaging or filtering procedures.