To Keep Your Eyes Healthy, Keep Your Blood Pressure Well-Controlled
Hypertension can lead to blindness
One of the most important things people with diabetes can do to keep their eyes healthy is maintaining normal blood pressure. High blood pressure (hypertension) causes harm to the eyes by creating excessive force against the fragile inner walls of the eyes' tiny blood vessels. As a result, the cells lining those blood vessels become damaged and stop working properly to maintain vascular health: blood, blood serum, blood fats, and blood proteins start to leak out, like water leaking from a garden hose that has tiny holes punched through it. The tiniest vessels – the capillaries – begin to close off, meaning that the tissues to which they bring blood and oxygen no longer receive adequate nourishment and start to die. If this process goes on long enough, vision will be lost.
In the absence of high blood glucose (hyperglycemia), very high blood pressure leads to exactly this kind of retinal damage, called hypertensive retinopathy. Moreover, high blood pressure raises the risk of several other eye diseases as well (including retinal vein and artery occlusion, and ischemic optic neuropathy). When blood glucose levels are high, as in diabetes, this process occurs at much lower levels of blood pressure because excess blood glucose itself damages the cells inside our blood vessels. In essence, there is a combination, "snowball" effect between hyperglycemia and hypertension that accelerates vascular injury and leads to diabetic retinopathy and other diabetes related vision loss.
In fact, several large diabetes studies have shown that blood pressure control is at least as important in preventing diabetic retinopathy as is blood glucose control. The United Kingdom Prospective Diabetes Study (UKPDS), the most famous study of type 2 diabetes, found that a 10/5 mm reduction in blood pressure (from 154/87 to 144/82) reduced the risk of diabetic retinopathy getting worse by 34% and the risk of significant vision loss by almost 50%! This begs the question, of course, "when it comes to blood pressure, how low is low enough?" A number of clinical trials are now being conducted to help answer this question, mainly with respect to cardiovascular disease. I'd like to briefly mention one study that addresses this question from the standpoint of sight-threatening diabetic retinopathy.
One team of researchers in Great Britain looked at the blood pressure and internal eye pressure of more than 1,300 people with diabetes seen for eye examination over a 20-year period. From these pressures, they calculated the "mean arterial pressure" (MAP) and "retinal perfusion pressure" (RPP) for each patient. MAP is the average pressure inside the artery where the blood pressure cuff is placed (usually at the crease of the elbow), and is based on a modified average of the top blood pressure reading (the systolic pressure) and the bottom reading (the diastolic pressure).For example, if your blood pressure is 120/80, 120 is the systolic pressure and 80 is the diastolic pressure. RPP is a measure of the force of normal blood flow into the eye, and is essentially the difference between a person's MAP and his internal eye pressure, which is commonly measured during virtually all eye examinations. So then, what did their research reveal?
High MAP and RPP strongly predicted which patients were most likely to develop severe, sight-threatening diabetic retinopathy (either proliferative retinopathy, or retinopathy with clinically significant macular edema, the two forms of the disease that can lead to severe vision loss or blindness.) In fact, patients with MAP and RPP levels in the highest quartile (25%) were 3-6 times more likely to develop severe retinopathy than patients with levels in the bottom 50%, and these levels actually predicted severe eye disease better than did duration of diabetes.
What does this all mean for those of us with diabetes? First, we should work with our physicians and modify our lifestyles to keep our blood pressure readings as low as is safely possible. Based on my own analysis of this study, maintaining a blood pressure of 115/75 or lower will place virtually every person with diabetes at the safest levels of MAP and RPP. Conversely, blood pressures above 130/82 place us at significantly higher levels of risk. Second, many if not most people with diabetes are nowhere near these targets, so we need to more openly discuss blood pressure goals and medicines with our physicians. Third, remember that this is only one study in a fairly homogenous (Anglo) population, that more research is still ongoing, and better treatments are on the horizon. For the time being, remember that tight blood glucose control and aggressive blood pressure control, combined with regular dilated eye examinations, is the best strategy for avoiding loss of vision from diabetes. For anyone interested in a more detailed discussion of these topics, you might want to check out my book, Diabetic Eye Disease: Lessons From a Diabetic Eye Doctor. Have a very happy and healthy New Year.
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NOTE: The information is not intended to be a replacement or substitute for consultation with a qualified medical professional or for professional medical advice related to diabetes or another medical condition. Please contact your physician or medical professional with any questions and concerns about your medical condition.
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