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Mathias Seeliger, Kristina Narfstrom, Naoyuki Tanimoto; Impact of the spectral output of “white” LEDs on the murine flash ERG. Invest. Ophthalmol. Vis. Sci. 2013;54(15):6127.
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Electroretinography (ERG) is a technique that uses standardized equipment and examination protocols to assess retinal function. Until recently, Xenon bulbs have been the best available technology to generate stimulus flashes, but now these are more and more replaced by LED stimulators. Here, we focus on the spectral differences between these stimulators, and discuss the impact on the outcome of scotopic and photopic recordings.
Functionally normal wild-type mice (C57Bl/6), mice with rod function only (Cnga3-/-), and mice with cone function only (rho-/-), were examined in vivo with Xenon and LED flash ERG systems. The results were related to the spectral properties of each stimulus type.
The spectral data of "white" LEDs reveal that their output peaks in the blue and yellow range, with a deep trough in the green range where rod sensitivity has its maximum (data from 5 different LED manufacturers). Due to this output spectrum being far from flat, it was tested whether a pure "white" LED stimulator does stimulate cones more efficiently than rods. This was indeed confirmed in in vivo recordings. In comparison to the cone system responses, the rod system responses came out relatively smaller with a LED system than with a Xenon system.
Comparing a LED stimulator ("white" LEDs) with a Xenon flash system, we found a definite impact on the outcome of scotopic but not photopic recordings. This does have a number of potential consequences for clinical and experimental ERGs. In diseases where rod sensitivity is lowered, a less efficient stimulation of the rod system may reduce the diagnostic performance. Further, to obtain a certain flash effect or a sufficiently rod-desensitizing background with such types of LEDs, the cone system would be stimulated more than necessary, with possibly altered behavior. The "unbalanced" stimulation of rods and cones due to an "unnatural" spectrum of the stimulus may further alter the interaction of rod and cone systems at different lighting conditions, and lead to distorted results in case of diseases that have a different impact on those systems (either intrinsically or as part for the degenerative process).
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