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M.V. Kyhn, J.F. Kiilgaard, E. Scherfig, J. Prause, M. la Cour; Multifocal electroretinogram (mfERG) and simultaneously monitoring of the fundus picture in the domestic pig. . Invest. Ophthalmol. Vis. Sci. 2004;45(13):4247.
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Purpose:mfERG recordings from the domestic pig have previous been presented without simultaneous monitoring of the fundus picture. An exact correlation between mfERG changes and local changes in the fundus is therefore difficult. The purpose of this study is to present a method for continuous fundus monitoring during mfERG recording and to correlate the mfERG amplitudes with previously established cone densities in the pig retina. Methods:The heavy pigmentation of the pig sclera and choroid made it impossible to visualize the fundus, and to obtain simultaneous mfERG recording, in the conventional manner, using the VERIS Science 5.0.1 (Electro–diagnostic Imaging, CA), and a conventional IR emitting Burian–Allen bipolar contact lens electrode. We therefore constructed an external IR–light source, transmitting perpendicular through the dilated pupil. This allowed continuous fundus monitoring through the camera unit, during the mfERG recording. Recordings were done on 10 domestic pigs (aged 3–4 months) with fully dilated pupils. Each animal was examined 3 times with an interval of one week and each time with recordings of both eyes. The visual stimuli consist of 241 unscaled hexagons, covering the central 20 degrees of retina, with a mean luminance of 100 cd/m2, m–exp: 15. Results: We have managed to establish a method for mfERG recordings, with simultaneous fundus monitoring. The mfERG recordings identify the presence of a visual streak/area centralis in the pig retina, located horizontal and superior to the optic disc, with amplitudes between 12–15 mV/deg2. Discussion: Histopathological studies (1,2) have previously described a visual streak in the pig retina, located horizontally above the optic disc. They identified a cone density in this area from 20.000 to 39.000 cones pr square mm. The functional studies of the same area, performed in this study, verify the presence of a high–cone–density area in the pig retina. The anatomical similarities between the human and porcine eye, makes the pig an ideal model for investigating retinal diseases. The method for simultaneously mfERG recording and fundus monitoring, presented here will enable us to study the effect of specific retinal lesions on local retinal functions. 1. Chandler et al. Photoreceptor density of the domestic pig retina. Vet Ophthamol 1999; 2: 179–184. 2. Hendrickson et al. Distribution and density of Medium– and Short–wavelength selective cones in the Domestic Pig Retina. Exp Eye Res 2002; 74: 435–444.
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