Influence of Red Blood Cell Aggregation on Choroidal Perfusion and Its Putative Meaning in the Progression of Age Related Macular Degeneration (AMD)

Abstract

Purpose:: For age related macular degeneration (AMD) the therapeutic situation is still unsatisfactory, especially for the dry form. Recent clinical trials showed that an amelioration of the rheological properties of the blood by Rheopheresis results in an advantageous influence on visual acuity. As mode of action it is postulated that this therapy counteracts worsening of choroidal perfusion in AMD. According to Friedman’s heaemodynamic model, this worsening of perfusion is decisively caused be a worsening of the vascular situation as arteriosclerotic alterations and rigidification of the sclera. Investigations of our group showed that especially under pathological vascular conditions changes of plasma viscosity have a strong influence on choroidal circulation. As therapies as Rheopheresis influence not only the plasma viscosity but red blood cell aggregation as well it was the aim of this investigation to analyze the role of red blood cell aggregation as an additional factor for the choroidal perfusion under physiological and pathological vascular situation.

Methods:: The experiments were performed on the isolated rat eye. The worsening of the vascular situation was simulated by varying the vessel diameter by adding different concentrations of Papaverin. Blood was replaced by red blood cell suspensions with defined rheological properties by changing the quantity of Ficoll within the ratio Ficoll/Thomadex in the plasma phase. Red blood cell aggregation was adjusted by a Myrenne aggregometer. Using computer controlled microangiography the percentate of the aerea exceeding a basal threshold was determined to characterize perfusion.

Results:: For wide vascular lumina a deterioration of red blood cell aggregation from aggregation index of 13 (physiological < 20) to 32 lead to no significant worsening of perfusion from 73 % (SD 6 %) to 72 % (SD 9 %). For narrow vessels on the other hand a deterioration of red blood cell aggregation from aggregation index of 13 (physiological < 20) to 32 lead to a significant worsening of perfusion from 71 % (SD 6 %) to 41 % (SD 9 %).

Conclusions:: For wide vascular lumina a deterioration of red blood cell aggregation from aggregation index of 13 (physiological < 20) to 32 lead to no significant worsening of perfusion from 73 % (SD 6 %) to 72 % (SD 9 %). For narrow vessels on the other hand a deterioration of red blood cell aggregation from aggregation index of 13 (physiological < 20) to 32 lead to a significant worsening of perfusion from 71 % (SD 6 %) to 41 % (SD 9 %).

Keywords: age-related macular degeneration • pathology: experimental • choroid