Standard for clinical electroretinography (1994 update)
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- Marmor MF, Arden GB, Nilsson SE, Zrenner E. Standard for clinical electroretinography. Arch Ophthalmal 1989; 107: 16–9.
- Prolonged-flash ERGs are currently used for studying slow potentials and off-responses that are outside the scope of the standard. We recognize that one can adjust the intensities of long flashes to produce response amplitudes equivalent to those produced by brief flashes; thus, standard ERG responses can be obtained from such longer stimuli. However, the procedure requires careful comparison of ‘V/log I’ curves and particular care to avoid interference from off-responses and signal attenuation by light adaptation (i.e., the interstimulus interval must be appropriately lengthened). The verification of equivalence to the standard ERG is recommended only for laboratories with special needs.
- Chromatic stimuli offer certain advantages in the separation of cone and rod responses, but the calibration of colored stimuli and the relation of the responses produced to the standard ERG requires special procedures. We recommend that white flashes be used for the standard responses in addition to other stimuli that may be used.
- This measurement can in practice be made with inexpensive light meters that integrate the flash output over time (see ‘Light Adjustment and Calibration’ section). Technically, the standard describes a source that delivers at the cornea the same number of quanta during the period of its flash as would be produced in 1 second by the ganzfeld bowl when continuously illuminated by a source that produces a luminance of 1.5–3.0 cd·m−2.
- We recommend that the flash source of commercial instruments be capable of generating strengths 1 log unit above the SF and be attenuable through 6 log units below the SF. Regardless of whether attenuation is achieved by filters or electronic means, we strongly recommend that commercial units incorporate a means of inserting additional colored and neutral density filters to meet a variety of individual (and unforeseen) needs. We also suggest that background luminance be adjustable to that electro-oculography can be performed with the same equipment. Commercial units should also allow the insertion of colored and neutral filters into the background illumination system to meet a variety of needs.
- Direct-current amplification can produce identical responses but is extremely difficult to use because of drift in baseline and in offset potentials; we strongly advise alternating-current recording except for laboratories with special requirements and expertise.
- Laboratories experienced in the use of noncontact lens electrodes (e.g., conductive fibers or foils) may elect to record photopic responses before scotopic ones, since there is less risk of corneal irritation from these electrodes over the time of dark adaptation. In this case, photopic adaptation is unnecessary as long as the patient has been at photopic light levels for at least 10 minutes before recording, but eyes should be dark adapted for at least 20 minutes before the scotopic responses are recorded.
- An overall index of oscillatory potential amplitude can be obtained by adding up measurements of the three major peaks, preferably from lines spanning the bases of the adjacent troughs, but alternatively from the adjacent troughs directly (to allow use of measuring cursors with digitized systems). Some authors advise measurement of individual peaks.
- Standard for clinical electroretinography (1994 update)
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