Introduction 1 2 Although the mfERG now has been used for more than 10 years to aid in the diagnosis of diseases of the retina, ISCEV decided that it is still premature to set specific standards. However, to take into consideration recent developments in technology and practice, this document provides revised guidelines for recording clinical mfERGs. These guidelines will be reviewed periodically, consistent with ISCEV’s practice. Description of multifocal electroretinography 1 Fig. 1 a b  2 Fig. 2 Diagram of an mfERG response to show the designation of the major features of the waveform  Basic technology Electrodes Recording electrodes 1 3 Reference and ground electrodes 1 3 Electrode characteristics, stability and cleaning 1 3 Stimulation Stimulus source 1 Frame frequency A CRT frame frequency of 75 Hz has been used widely. (LCD displays use 60 Hz.) Use of different frequencies can substantially alter the amplitude and waveform of the mfERG response. Whatever frame frequency is used, normative values for normal healthy subjects need to be determined separately for that frequency. Further, it is essential to specify the frame frequency when reporting results. Luminance and contrast 2 2 Calibration 4 Stimulus parameters Stimulus pattern Flicker sequence Stimulus size and number of elements Fixation targets Recording, analyzing and presenting results Amplifiers and filters The gain of the amplifier should produce recognizable signals without saturation. Appropriate band-pass filtering removes extraneous electrical noise, without distorting waveforms of interest. For a “standard” mfERG, the high pass cutoff can range between 3 and 10 Hz and the low pass cutoff between 100 and 300 Hz. Filter settings, even within the ranges suggested, will influence the response waveform. Thus, the filter settings should be the same for all subjects tested by a given laboratory, as well as for the norms to which they are compared. Line-frequency or notch filters should be avoided. Signal analysis Artifact rejection Spatial averaging Displaying results Trace arrays 3 3 4 Fig. 3 a b c d a b  Fig. 4 The mfERG trace array (left panel, field view) and the probability plot from standard automated perimetry (right panel) for a patient with retinitis pigmentosa. The contours for a radius of 5 and 15° are shown. The light gray, dark gray, and black squares indicate statistically significant field loss at the 5, 1 and 0.5 percent levels, respectively  Group averages 5 3 5 5 Fig. 5 c a b  Topographic (3-D) response density plots 3 Signal extraction: Kernels Clinical protocol Patient preparation Pupils The pupils should be fully dilated and pupil size noted. Patient positioning Subjects should sit comfortably in front of the screen. Relaxation of facial and neck muscles will reduce artifacts from muscles; a headrest may be helpful. The appropriate viewing distance will vary with screen size, in order to control the area (visual angle) of retina being stimulated. Fixation monitoring Good fixation, both central and steady, is essential. Thus, fixation should be monitored, preferably by the use of monitoring instrumentation available on some units. When this option is not available, careful direct observation may be employed. Refraction Although there is some evidence that the mfERG is unaffected by moderate blurring of the retinal image in healthy individuals, we recommend refraction for optimal acuity. On some commercial machines, a manual adjustment of the viewing optics is possible. Alternatively, lenses can be placed in a holder positioned in front of the eye. In the latter case, the viewing distance must be adjusted to compensate for the relative magnification of the stimulus. Also care must be taken to avoid blocking the view of the stimulus screen by the rim of the lens or the lens holder and thus creating an apparent scotoma. Monocular versus binocular recording Recording is typically done with monocular stimulation. Those who record binocularly should be aware that signals can be altered by misalignment of the eyes. Adaptation Pre-adaptation  before test Room illumination Stimulus and recording parameters Stimulus Size The stimulus should subtend 20–30° of visual angle on either side of the fixation point. Number of elements A display containing 61 or 103 elements should be used. Duration of recording A total recording time of at least 4 min for 61 element arrays, or 8 min for 103 element arrays, is recommended, although these times might be adjusted by experienced laboratories according to clinical needs. The overall recording time is divided into shorter segments (e.g. 15–30 s) so that subjects can rest between runs if necessary and also so that a poor record (from noise, movement or other artifacts) can be discarded and repeated without losing prior data. Trade-offs Various manipulations will affect the signal-to-noise ratio (SNR) of the responses. In particular, decreasing the size (increasing the number for a fixed stimulus field size) of the stimulus elements and decreasing the duration of the recording will decrease the SNR of the responses. While decreasing the number (increasing the size) of elements will increase the SNR, it will decrease the spatial resolution of the test. In general, conditions with larger (i.e. 61) elements and a shorter recording time (e.g. 4 min) are easier for the patient and suitable for a general screening of macular function. On the other hand, conditions with 103 elements and a longer recording time (e.g. 8 min) are useful for assessing foveal function and mapping the outline of retinal defects. Very small elements (such as a 241 hexagon array) may sometimes be helpful for diseases with very small or irregular effects. Repeat recording is recommended to confirm small or subtle abnormalities. Further, the choice of electrode type will also influence the SNR of the responses. For example, bipolar corneal contact electrodes yield recordings with the highest SNR. Thus, longer recording times, repeat measurements and/or fewer stimulus elements are necessary to obtain comparable SNRs when a foil or fiber electrode is used. Data reporting Mode of display Trace arrays 3 Group averages 5 Three-dimensional plots 3 Measurements calibration marks Measuring mfERG amplitude and timing 2 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 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.