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E. Friedman; The Role of Blood Pressure in the Pathogenesis and Management of Diabetic Retinopathy and Age Related Macular Degeneration . Invest. Ophthalmol. Vis. Sci. 2003;44(13):1704.
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Purpose: In Western and developing countries Diabetic Retinopathy (DR) is the major cause of irreversible blindness for those under the age of 74, and Age Related Macular Degeneration (AMD) is the major cause after that age. Together the two disorders are responsible for most vision loss. Methods: Systemic hypertension has long been recognized as a modifiable risk factor for both DR and AMD. Considering the potential public health impact, ophthalmologists may not be giving optimal control of hypertension the emphasis that it deserves in the management of either disorder. This can be attributed in part to the lack of consensus on their pathogenesis in general and on the importance of hemodynamic factors in particular. It is the purpose of this paper attempt to highlight the hemodynamic phenomena in isolation. Results: In a paper on the pathogenesis of DR and nephropathy, Parving et al (1983) pointed out that: 1) mean capillary hydrostatic pressure (Pc) is a function of the arterial and venous pressures and the ratio of the resistances to the flow of blood in the venular and arteriolar capillaries (Rv/Ra). 2) the increased rate of retinal blood flow that characterizes early DR is associated with a decrease in precapillary (Ra). 3) this results in an increase in (Pc) and 4) the microvascular pathology associated with early diabetic retinopathy can be accounted for by the increased intravascular pressure. There is evidence that AMD is characterized by: 1) an increase in postcapillary resistance to choroidal blood flow (Rv), leading to an elevation of the ratio Rv/Ra and an increase in the mean capillary hydrostatic pressure (Pc) and 2) histopathologic and angiographic changes which suggest an elevated capillary pressure (Pc) may, at least in part, be responsible the clinical picture known as exudative or neovascular AMD. Conclusions: Thus, the mean capillary pressure (Pc) of both disorders will be increased, DR by a decrease in precapillary resistance (Ra) of the retinal vessels, AMD by an increase in postcapillary resistance (Rv ) of the choroidal vessels. Systemic hypertension is a risk factor for both disorders because an elevated systemic blood pressure will raise an already high capillary pressure past the point of vascular decompensation.
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