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M.F. Marmor; Rapid S-Cone ERG Recording With a Modified Diagnosys Recording Handpiece . Invest. Ophthalmol. Vis. Sci. 2003;44(13):4875.
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Purpose: S-cone involvement has been shown in many retinal diseases and may be a useful marker for early retinal damage. However, the S-cone ERG has been difficult to record without compex equipment or extended procedures. We have sought a simple procedure for documenting the S-cone ERG that might be incorporated into routine testing. Methods: The Diagnosys ERG recording unit is a commercial instrument with an LED-driven handpiece dome stimulator, that is held over the eye. The standard unit has red, green and blue LEDs, with the peak emission of the green at 510 nm and the blue at 461 nm. We also obtained a special handpiece with red, orange (peak at 590 nm) and deeper blue (peak at 440 nm) LEDs. ERG recordings were made on normal subjects and a patient with enhanced S cone syndrome (ESCS). Results: Using the special handpiece with a 300 cd/m2 orange background, low intensity 440 nm blue flashes at 4 Hz produced within a few seconds a well-defined slow ERG response peaking near 50 ms in normal subjects. Low-intensity orange flashes produced a more rapid waveform with a typical L and M cone peak near 30 ms. Very strong blue flashes produced a combination of the faster and slower peaks. The patient with ESCS showed only the slow peak to either blue or orange flashes, which supported the conclusion that this was an S-cone ERG. An S-cone response could also be produced using flicker stimuli by balancing blue and orange stimuli intensities at 30 Hz to produce a minimal (null) waveform, and then recording with the same intensities at 4Hz. However, this procedure was more time-consuming than the blue flash on orange background procedure. With the conventional hand piece, using a yellow/orange background or using the flicker procedure, most normal subjects did not show any recognizable S-cone response. Conclusions: S-cone ERGs can be recorded rapidly and reliably from normal subjects using a Diagnosys handpiece with 440 nm blue LEDs and no green LEDs. It remains to be shown whether this procedure will have value in routine ERG testing. The failure to record S-cone ERGs with the standard handpiece may relate both to the longer blue wavelength (that may overlap M cone sensitivity) and the fact that background colors were generated partly by green LEDs (that may overlap and suppress S cone sensitivity).
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