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Y Shimada, M Horiguchi, A Nakamura, T Sugino; On-disc ERG reveals stray light effects in the multifocal ERGs . Invest. Ophthalmol. Vis. Sci. 2002;43(13):1791.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose:In multifocal electroretinogram (mfERG), local ERG responses can be observed even on the stimulus elements corresponding to the optic disc (on-disc ERGs). As there is no photoreceptor on optic disc, on-disc ERGs were due to stray light effects. We investigate on-disc ERG in order to figure out the latent features of stray light effects in the multifocal technique. Methods:32-year-old female served as subject. She has optic disc coloboma with remarkable enlargement of optic disc in the right eye. While the blind spot is dilated and threatening the foveal vision, the corrected visual acuity is 20/20. Using stimulus geometry with 37 elements, four of them projected entirely onto the optic disc. Various stimulus intensities were applied to record mfERG. Results:With our default stimulus settings (75 Hz base rate, 2.67 cd·s/m2 flash intensity), on-disc ERG was one half as large as ERG from the other retinal area excluding the optic disc and marginal region. Dimmer flashes evoked relatively smaller on-disc ERG and the implicit time of it was much further prolonged. The second order kernel response of on-disc ERG was almost flat throughout all recordings. Conclusion:1. There was some compromised interpretation that the stimulus element corresponding to optic disc projects also on the marginal region of retina so that it does not provide totally flat response. However, even if the stimulus element sufficiently fits the optic disc, its flash generates certain on-disc ERG owing to the light scattering. Awareness of the stray light effect helps bring about better comprehension and avoid misinterpretation of mfERG. 2. Many clinical and scientific papers attribute the selective reduction of the second order kernel responses to the dysfunction in inner retinal layer. Our finding did not deny it, however, stray light effect also produces the quite similar selective reduction upon totally different mechanism. 3. On-disc ERG does not contain the second order kernel responses, so the second order kernel properties were little affected by stray light effect. The better locality should be of advantage in the second order kernel analysis.
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