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R. Ejstrup, E. Scherfig, M. la Cour; A Novel Porcine Model for Retinal Ischemia: Electrophysiological Consequences of Branch Retinal Vein Occlusion (BRVO) and Dorzolamide. Invest. Ophthalmol. Vis. Sci. 2010;51(13):3585.
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© ARVO (1962-2015); The Authors (2016-present)
To study the consequences of experimental BRVO in pigs on the multifocal electroretinogram (mERG) and the effect of the carbonic anhydrase inhibitor Dorzolamide in this model.
In general anaesthesia BRVO was induced in right eyes of 16 Danish Landrace pigs by diathermia of the superior retinal vein without vitrectomy. Four weeks post surgery the animals were examined bilaterally with 103 unscaled hexagons mERG before and after administration of 500mg Dorzolamide or saline IV in a randomized and blinded fashion. Fundus photography (FP), indirect ophthalmoscopy and fluorescence angiography (FA) were performed before the animal was sacrificed. The BRVO affected hexagons of the mERG were grouped by aligning the infrared picture from the mERG recording with the FP. The corresponding area of the healthy fellow eye was selected. The P1 amplitudes were used to quantify outer retinal responses (P1) and a four-frame mERG protocol was used to quantify inner retinal responses (iN1).
Four animals were excluded due to retinal detachment resulting in 6 animals in the Dorzolamide group as well as in the saline group. After four weeks all BRVO eyes displayed signs of retinal damage in the effected area on FP, FA and ophthalmoscopy.The initial mERGs before Dorzolamide/saline revealed a marked drop in both inner and outer retinal responses in BRVO areas as the ratio of BRVO/fellow eye decreased for both P1 0.30 (CI 0.20-0.45, p<0.0001) and iN1 0.35 (CI 0.23-0.54, p<0.0001). After Dorzolamide/saline no significant difference between groups existed for P1 but for iN1 components ratios were significantly higher in Dorzolamide treated eyes 0.97 (CI 0.74-1.26) than placebo eyes 0.43 (CI 0.30-0.62, p=0.005). In healthy eyes there was a significant change in ratios of inner retinal function before and after Dorzolamide 0.29 (CI 0.19-0.44) compared to before and after saline 0.57 (CI 0.42-0.78, p=0.026). This difference was not significant for P1.
Surgical induction of BRVO causes reduction of the inner and outer retinal components of the porcine mERG. Responses are not vanished but diminished to about one third of healthy retina. Normal retina responds to Dorzolamide by lowering of amplitudes of inner retinal component iN1 a feature that is lost in BRVO affected areas possibly due to an increase in blood flow and inner retinal oxygenation in the ischemic area.
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