Hypertension is classified as being either primary hypertension or secondary hypertension. 90-95% of cases are primary hypertension, which means high blood pressure, usually defined as a repeatedly elevated blood pressure exceeding 140 over 90 mmHg (a systolic pressure above 140 with a diastolic pressure above 90). Secondary hypertension is caused by other conditions that affect the kidneys, arteries, heart or endocrine system. Hypertension can cause such conditions as blood vessel changes in the retina (at the back of the eye), abnormal thickening of the heart muscle, kidney failure, and brain damage. Regular blood pressure checks help with diagnosis. In most cases, no specific cause is found. Hypertension is treated with regular aerobic exercise, weight reduction for those overweight, salt restriction, and medications to control blood pressure.