No doubt you're aware of the ocular manifestations of primary hypertension, but do you know about the medications to treat it, or its risk factors? Here, I'll tell you about this silent killer, which affects more than 30% of U.S. adults.

Regulating blood pressure

Changes in kidney function and in the autonomic nervous system control blood pressure. Under stress, the sympathetic branch of the autonomic nervous system increases the rate and force of the heartbeats.

Most arterioles constrict, except those in the skeletal muscles, which dilate. The sympathetic nervous system also decreases the kidneys' excretion of salt and water. This causes an increase in blood volume, and an increase in blood pressure. The sympathetic nervous system also releases the hormones epinephrine (adren-
aline) and norepinephrine (noradrenaline), which stimulate the heart and blood vessels.

The kidneys control blood pressure. Should the blood pressure increase, the kidneys excrete salt and water to decrease blood volume and pressure. Conversely, if blood pressure decreases; the kidneys reduce their excretion of salt and water. The kidneys can also increase blood pressure by secreting the enzyme renin. This enhances production of the hormone angiotensin, which triggers the release of aldosterone.

For example, if blood pressure decreased, renin released by the kidneys would activate angiotensin, causing the arterioles to constrict and increasing blood pressure. In addition, angiotensin stimulates the release of aldosterone from the adrenal glands. Due to aldosterone, the kidneys retain salt (sodium) and excrete potassium. The sodium osmotically retains water, thus expanding the blood volume and increasing blood pressure.

Risk factors for hypertension

Two major types of hypertension exist.

�         Primary hypertension. In approximately 90% of hypertensive patients, the etiology is unknown. These cases are known as "essential" or "primary" hypertension.
The etiology is probably multifactorial. As we age, blood pressure increases, probably secondary to arteriosclerosis. Arteriosclerosis prevents the dilation of the arteries that would normally lower blood pressure. In addition, arteriosclerotic changes in the kidneys can impair their ability to excrete salt and water.
Though the exact etiology of primary hypertension is unknown, risk factors include:

o       African-American race

o       family history

o       being a male older than 35

o       being a post-menopausal female

o       eating a high salt/high fat diet

o       obesity

o       smoking

o       excessive consumption of alcohol

o       diabetes mellitus

o       sedentary lifestyle or stress.

�         Secondary hypertension. When the etiology of hypertension is known, it's called secondary hypertension. In 5% to 10% of hypertensive people, the cause is kidney disease. In 1% to 2%, a hormonal disorder is to blame. A rare cause of hypertension is pheochromocytoma, a tumor of the adrenal glands (which secretes excessive amounts of epinephrine and norepinephrine). Other causes of secondary hypertension are:

o       renal artery stenosis

o       pyelonephritis

o       glomerulonephritis

o       polycystic kidney disease

o       hyperaldosteronism

o       Cushing's syndrome

o       use of drugs such as corticosteroids, cyclosporines, erythropoietin and cocaine.

Classifying hypertension

Hypertension is classified according to systolic and diastolic blood pressure readings. In general, a systolic reading below 130 mm Hg is considered normal, as is a diastolic reading below 85 mm Hg. Hypertension is defined as systolic blood pressure exceeding 140 mm Hg and/or a diastolic pressure exceeding 90 mm Hg measured at least twice on separate days.

Complications of hypertension

In most people, hypertension causes no overt symptoms. It's often a silent killer. Severe, chronic or untreated hypertension will damage the brain, heart, kidneys and eyes.

�         Systemic complications. Arteriosclerosis and atherosclerosis are significant risk factors in the development of hypertension. The deposition of lipids in the blood vessels causes a loss of elasticity and subsequent rise in blood pressure. Thrombus and embolus formation are possible. In addition, when blood vessels narrow, they impair blood flow and causes ischemic disease. The increased systemic vascular resistance to blood flow makes the heart work harder. Coronary heart disease is the leading cause of death among hypertensive patients.
Cerebrovascular disease is also a serious complication of hypertension. Hypertension often leads to stroke or aneurysm. In addition, hypertension-induced arteriosclerosis may cause the atrophy of the renal glomeruli and tubules, leading to renal failure.

�         Ocular complications. Hypertension has ocular complications, including the following:

o       retinal vessel occlusion

o       ocular ischemic syndrome

o       ischemic optic neuropathy

o       ophthalmoplegia

o       cranial nerve palsy

o       nystagmus

o       amaurosis fugax (transient blindness).

Hypertensive retinopathy

Narrowing of the arterioles characterizes hypertensive retinopathy. The amount of narrowing is usually related to the severity of the diastolic hypertension. If the hypertension is left untreated, arterial-venous crossing changes result. The changes start with a deflection in the course of the vein, followed by tapering and constriction of the vein on either side of the crossing arteriole. Finally, with continuing hypertension, retinal hemorrhages and exudates develop. The flame-shaped hemorrhages are located in the nerve fiber layer of the retina.

Soft cotton-wool exudates can appear with an acute rise in pressure. In severe hypertension, hard exudates may also occur.

Papilledema may also result from severe hypertension. This is a very grave sign; 5-year mortality of patients with hypertensive papilledema is more than 90%.

Treatment of hypertension

Primary hypertension is chronic and incurable, but it can be controlled. Lifestyle changes are often necessary:

�         Overweight patients should lose weight.

�         Salt-sensitive patients should reduce their salt intake to 6 grams per day but maintain adequate intake of calcium, magnesium and potassium.

�         Moderate aerobic exercise helps.

�         Patients must stop smoking!

Pharmaceutical intervention

If lifestyle modifications don't reduce blood pressure, medication is required. Five classes of drugs are used to control hypertension. They are:

�         Diuretics. Diuretics are usually prescribed first. They allow the kidneys to more easily eliminate salt and water, reducing blood volume and pressure.

�         Adrenergic blockers (including alpha- and beta-blockers).These "block" the effects of the sympathetic nervous system. This system responds to stress by raising blood pressure. Beta-blockers are generally well tolerated, but they're not a good choice for patients with asthma or chronic obstructive pulmonary disease because they may cause respiratory distress.

�         Angiotensin-converting enzyme (ACE) inhibitors and Angiotensin II blockers. ACE inhibitors lower blood pressure by dilating arteries. Angiotensin II blockers also lower blood pressure this way, and cause fewer side effects. However, these medications aren't good for patients who have elevated renin levels, because they may have an exaggerated hypotensive response.

�         Calcium antagonists. Calcium antagonists (or calcium-channel blockers) control hypertension by vasodilatation. These medications are well tolerated and have become popular as anti-hypertensives. They are, however, among the most expensive treatments for hypertension.
Calcium antagonists aren't good for patients with severe liver disease, because they're metabolized in the liver.

�         Direct vasodilators.These drugs are rarely used alone. They're very potent and are generally reserved for refractory cases. The drugs in this class are hydralazine hydrochloride (Apresoline) and minoxidil (Loniten).

Lifesaver

As a primary care optometrist, you're in a position to save a life. Measure your patients' blood pressure carefully and take action where needed.

Dr. Giardina is optometric director at Mission Medical Center in San Luis Obispo, Calif. He's a fellow of the AAO and adjunct professor of optometry at Southern College of Optometry in Memphis.

SELECTED ANTIHYPERTENSIVE MEDICATIONS

 CLASSIFICATION OF BLOOD PRESSURE