ISCEV standard for clinical multifocal …

1 ISCEV STANDARDSISCEV standard for clinical multifocal electroretinography(mfERG) (2011 edition)Donald C. Hood Michael Bach Mitchell Brigell David Keating Mineo Kondo Jonathan S. Lyons Michael F. Marmor Daphne L. McCulloch Anja M. Palmowski-Wolfe For the International Society For clinical Electrophysiology of VisionReceived: 9 October 2011 / Accepted: 12 October 2011 / Published online: 30 October 2011 Springer-Verlag 2011 AbstractThe clinical multifocal electroretinogram(mfERG) is an electrophysiological test of local retinalfunction. With this technique, many local ERGresponses are recorded quasi-simultaneously fromthe cone-driven retina under light-adapted document, from the International Society forClinicalElectrophysiologyofVision( ), replaces the ISCEV guidelines forthe mfERG published in 2007. standards for perfor-mance of the basic clinical mfERG test with a stimulusarray of 61 or 103 hexagons, as well as for reportingthe results, are guidelines Electroretinogram multifocal electroretinogramAbbreviationsCRTC athode ray tubeERGE lectroretinogramISCEVI nternational Society for ClinicalElectrophysiology of VisionLCDL iquid crystal displaymfERGM ultifocal electroretinogramPERGP attern electroretinogramD.

2 C. Hood (&)Departments of Psychology and Ophthalmology,Columbia University, New York, NY, USAe-mail: , Freiburg, GermanyM. BrigellTranslational Medicine, Novartis Institutes forBiomedical Research, Cambridge, MA, USAD. KeatingDepartment of Ophthalmology, Gartnavel GeneralHospital, Glasgow, UKM. KondoDepartment of Ophthalmology, Mie University GraduateSchool of Medicine, Tsu, JapanJ. S. LyonsWashington Hospital Center Program in Ophthalmology,Georgetown University, Silver Spring, MD, USAM. F. MarmorByers Eye Institute at Stanford, Stanford UniversitySchool of Medicine, Palo Alto, CA, USAD. L. McCullochVision Sciences, Glasgow Caledonian University,Glasgow, UKA. M. Palmowski-WolfeDepartment of Ophthalmology, University of Basel,Basel, Switzerland123 Doc Ophthalmol (2012) 124:1 13 DOI electroretinogram (ERG) is a mass potential,which reflects the summed electrical activity of theretina.

3 Full-field electroretinography is a well-estab-lished clinical technique for evaluating global retinalfunction [1]. The multifocal ERG (mfERG) techniquewas developed to provide a topographic measure ofretinal electrophysiological activity. With this tech-nique, many local ERG responses, typically 61 or 103,are recorded from the cone-driven retina under light-adapted conditions. In 2003, the International Societyfor clinical Electrophysiology of Vision ( ISCEV )published guidelines for recording the mfERG [2]and these guidelines were revised in 2007 [3]. Bothdocuments were guidelines, not standards , to allow forfurther research before standards were standard , which supersedes earlier ISCEVG uidelines for multifocal electroretinography [3],defines minimum protocols for basic clinical mfERGrecording and reporting.

4 The details of this protocolare less prescriptive than other ISCEV example, a range of values is allowed for boththe luminance of the stimuli and the filtering by theamplifiers. There are a number of reasons for thisdecision. The first is that the technology for producingthe stimulus display is rapidly evolving, with resultantdifferences in stimulus parameters. Second, there areno data to support the superiority of any single variantin producing repeatable results or in sensitivity toretinal disease. Thus, any of these technologies canproduce clinically acceptable basic mfERG , the mfERG is primarily used in the clinic tolocalize damage spatially, so that variations in thetopographic array of signals are more important thanabsolute signal size. This standard defines the limitswithin which stimuli and recording conditions shouldlie as well as standardized modes of display so thatresponses can be recognized and compared fromdifferent laboratories standard defines the conditions and proce-dures for a basic mfERG.

5 It is important to keep anumber of caveats in mind. First, the mfERG test doesnot replace the full-field ERG test. If pan retinaldamage or damage to the rod system is suspected, thenthe ISCEV full-field ERG protocol [1] should befollowed. Second, obtaining useful and reproduciblemfERG recordings requires all the care that isneeded for successful full-field ERG recordings, plusadditional requirements, as described below. Third,this standard only covers the primary use of themfERG, which is to identify damage to the retina up toand including the inner nuclear layer. Experiencedusers may wish to add other test protocols or modifyprocedures in order to optimize the test for certainclinical has also published guidelines for calibrationof electrophysiologic equipment [4], and standards forfull-field ERGs [1], pattern ERGs [5], the electrooc-ulogram [6], and visual evoked potentials [7].

6 Thisstandard will be reviewed periodically to incorporatedevelopments and reflect current of multifocal electroretinographyThe mfERG technique is a method of recording localelectrophysiologic responses from different regions ofthe retina. Electrical responses from the retina arerecorded with a corneal electrode as in conventional,full-field ERG recording. However, the nature of thestimulus and the form of the analysis differ. Thesedifferences allow a topographic map of local ERGactivity to be measured. For the basic mfERGdescribed here, the retina is stimulated with an arrayof hexagonal elements, each of which has a 50%chance of being illuminated every time the framechanges ( ). Although the pattern appears toflicker randomly, each element follows the samepseudo-random sequence of illumination with thestarting point displaced in time relative to otherelements.

7 By correlating the continuous ERG signalwith the sequence of on- and off-phases of eachelement, each local ERG signal is these local ERG signals are referred to asmfERG responses, it is important to keep in mind thatthey are not direct electrical potentials from localregions of retina, but rather they are a mathematicalextraction of the signal. Further, because the stimula-tion rate is rapid, the waveform of the local mfERGresponse can be influenced both by preceding andsubsequent stimuli, as well as by the responses to lightscattered on other retinal typical waveform of the basic mfERG response(also called the first-order response or first-orderkernel) is a biphasic wave with an initial negativedeflection followed by a positive peak ( ). Thereis usually a second negative deflection after the2 Doc Ophthalmol (2012) 124:1 13123positive peak.

8 These three peaks are called N1, P1, andN2, respectively. There is evidence that N1 includescontributions from the same cells that contribute to thea-wave of the light-adapted, full-field ERG and that P1and N2 include contributions from the cells contrib-uting to the light-adapted b-wave and oscillatorypotentials. Although there are homologies between themfERG waveform and the conventional ERG, thestimulation rates are higher for the mfERG and, asnoted above, the mfERG responses are mathematicalextractions. Thus, technically the mfERG responsesare not low-amplitude ERGs . Therefore, the desig-nations a-wave and b-wave, used for full-fieldERGs, are not appropriate to describe features of themfERG technologyElectrodesRecording electrodesElectrodes that contact the cornea, or nearby bulbarconjunctiva, are required.

9 This includes contact lens,foil, and fiber electrodes. In addition, good retinal imagequality and proper refraction are desirable. The choiceof electrode type can influence the signal-to-noise ratio(SNR) of the responses. For example, bipolar cornealcontact electrodes typically yield recordings with thehighest SNR. Thus, longer recording times, repeatmeasurements, and/or fewer stimulus elements arenecessary to obtain comparable SNRs when using afoil or fiber and ground electrodesProper application of suitably conductive electrodes isessential for reliable mfERG recordings. Recordingsare comparable only when the same electrode typesand locations are used. Follow the recommendationsmade in other ISCEV standards [1,5].Electrode characteristics, stability, and cleaningPoor or unstable electrode contact is a major cause ofpoor-quality records.

10 It is important to follow therecommendations concerning fiber, foil, loop, andcontact lens electrodes in the full-field ERG standard [1] and Pattern ERG (PERG) standard [5].StimulationStimulus sourceUntil recently, mfERG stimuli were most commonlydisplayed on a cathode ray tube (CRT). CRT monitorsABFig. 1 aRepresentative hexagonal mfERG stimulus array with 61 elements scaled with eccentricity. Roughly half of the elements areilluminated at any one as inpanel Afor an array with 103 elementsFig. 2 Diagram of a mfERG response to show the designationof the major features of the waveform. Thearrowsshow thetrough-to-peak amplitude (vertical arrow) and the implicit time(horizontal arrow) of the basic mfERG measures of amplitudeand timingDoc Ophthalmol (2012) 124:1 133123are being rapidly replaced with other devices such asliquid crystal displays (LCDs).