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S. Hecht, T. Kirschkamp, C. Bueb, S. Peters, N. Konieczny, A. W. A. Weinberger, H. Schmid-Schönbein, P. Walter; Choroidal Perfusion Disorders and Their Putative Consequences for the Progression of Age Related Macular Degeneration (AMD). Invest. Ophthalmol. Vis. Sci. 2007;48(13):3032.
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An adequate and economic therapy is not available for the treatment of the dry form of age related macular degeneration of the eye (AMD), mayor cause of blindness in industrial nations. Actual clinical trials presented that an amelioration of rheological properties of blood by Rheopheresis results in an advantageous influence on visual acuity. As mode of action it is postulated that this therapy counteracts the worsening of choroidal perfusion in AMD. According to Friedman’s heaemodynamic model, this worsening of perfusion is decisively caused by a worsening of the vascular situation as arteriosclerotic alterations and rigidification of the sclera. So this investigation was undertaken to analyze the dependence of choroidal perfusion on physiologic and pathologic bloodflow conditions.
The experiments were performed on isolated rat eye. Blood was replaced by red blood cell/thomadex suspensions with defined physiological rheological properties (plasma viscosity = 1,2 mPa s, hct = 44 %). The worsening of the vascular situation was simulated by varying the perfusion pressure of the choroidal vessels. Using computer controlled microangiography the percentate of the aerea exceeding a basal threshold was determined to characterize perfusion (n = 5 in each pressure group).
Within the perfusion pressure range from 200 to 110 mm Hg we found no measurable reduction of perfused area: For 200 mm Hg the perfused area was 95 % (SD 1 %), for 110 mm Hg it was 94 % (SD 1 %). However, during lowering perfusion preassure under 110 mm Hg, even minor preasure reductions lead to dramatic perfusion breakdown: For 100 mm Hg the perfused area was 69% (SD 7 %), for 90 mm Hg it was only 26 % (SD 5 %).
Between physiololgical (200 - 110 mm Hg) and pathological (90 mm Hg) choroidal perfusion, we found only a very small zone of perfusion changing over from physiological into pathological perfusion at 100 mm Hg. It seems that within this range of change over, where perfusion depends on perfusion conditions in a extremely sensitive way, already a minimal amelioration of rheological properties (as induced by plasmapheresis in AMD) can optimize perfusion distinctive. So, Rheopheresis seems to be a senseful way of optimizing choroidal perfusion. Recent investigations pointed out the role of disturbed choroidal microcirculation in resulting in maintaining pathological immunological and inflammatory processes finally leading to irreversible degeneration of neurosensorial retina.
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