The term ocular hypertension usually refers to any situation in which the pressure inside the eye, called intraocular pressure, is higher than normal. Eye pressure is measured in millimeters of mercury (mm Hg). Normal eye pressure ranges from 10-21 mm Hg. Ocular hypertension is an eye pressure of greater than 21 mm Hg.
Although its definition has evolved through the years, ocular hypertension is commonly defined as a condition with the following criteria:
- An intraocular pressure of greater than 21 mm Hg is measured in one or both eyes on 2 or more occasions. Pressure inside the eye is measured using an instrument called a tonometer.
- The optic nerve appears normal.
- No signs of glaucoma are evident on visual field testing, which is a test to assess your peripheral (or side) vision.
- To determine other possible causes for your high eye pressure, an ophthalmologist (a medical doctor who specializes in eye care and surgery) assesses whether your drainage system (called the "angle") is open or closed. The angle is seen using a technique called gonioscopy. This technique involves the use of a special contact lens to examine the drainage angles (or channels) in your eyes to see if they are open, narrowed, or closed.
- No signs of any ocular disease are present. Some eye diseases can increase the pressure inside the eye.
Systemic hypertension (high blood pressure)
Blood pressure is the force in the arteries when the heart beats (systolic pressure) and when the heart is at rest (diastolic pressure). It's measured in millimeters of mercury (mm Hg). High blood pressure (or hypertension) is defined in an adult as a blood pressure greater than or equal to 140 mm Hg systolic pressure or greater than or equal to 90 mm Hg diastolic pressure.
High blood pressure directly increases the risk of coronary heart disease (which leads to heart attack) and stroke, especially when it's present with other risk factors.
Viewing your retina during an eye exam is like looking into a window to the body. Because your retinal vascular system is visible during an eye exam it is possible to see changes in the size and pattern of your retinal arteries.
Who is at risk for ocular hypertension?
Although some studies have reported a significantly higher average intraocular pressure in women than in men, other studies have not shown any difference between men and women.
- Some studies suggest that women could be at a higher risk for ocular hypertension, especially after menopause.
- Studies also show that men with ocular hypertension may be at a higher risk for glaucomatous damage.
Intraocular pressure slowly rises with increasing age, just as glaucoma becomes more prevalent as you get older.
- Being older than 40 years is considered to be a risk factor for the development of both ocular hypertension and primary open-angle glaucoma.
- Elevated pressure in a young person is a cause for concern. A young person has a longer time to be exposed to high pressures over a lifetime and a greater likelihood of optic nerve damage.
What causes ocular hypertension?
Elevated intraocular pressure is a concern in people with ocular hypertension because it is one of the main risk factors for glaucoma.
High pressure inside the eye is caused by an imbalance in the production and drainage of fluid in the eye (aqueous humor). The channels that normally drain the fluid from inside the eye do not function properly. More fluid is continually being produced but cannot be drained because of the improperly functioning drainage channels. This results in an increased amount of fluid inside the eye, thus raising the pressure.
Another way to think of high pressure inside the eye is to imagine a water balloon. The more water that is put into the balloon, the higher the pressure inside the balloon. The same situation exists with too much fluid inside the eye—the more fluid, the higher the pressure. Also, just like a water balloon can burst if too much water is put into it, the optic nerve in the eye can be damaged by too high of a pressure.
Who is at risk for systemic hypertension?
High blood pressure can occur in children or adults, but it's more common among people over age 35. It's particularly prevalent in African Americans, middle-aged and elderly people, obese people, heavy drinkers and women taking birth control pills. It may run in families, but many people with a strong family history of high blood pressure never have it. People with diabetes mellitus, gout or kidney disease are more likely to have high blood pressure, too.
What causes systemic hypertension?
In about 10% of people, high blood pressure is caused by another disease (this is called secondary hypertension). In such cases, when the root cause is treated, blood pressure usually returns to normal. These causes of secondary hypertension include the following conditions:
- Chronic kidney disease
- Tumors or other diseases of the adrenal gland
- Coarctation of the aorta - A narrowing of the aorta that you are born with that can cause high blood pressure in your arms
- Use of birth control pills
- Alcohol addiction
- Thyroid dysfunction
In the other 90% of cases, the cause of high blood pressure is not known (referred to as primary hypertension). Although the specific cause is unknown, certain factors are recognized as contributing to high blood pressure.
What are the symptoms of ocular hypertension?
Most people with ocular hypertension do not experience any symptoms. For this reason, regular eye examinations are very important to rule out any damage to the optic nerve from the high pressure.
What are the symptoms of systemic hypertension?
High blood pressure usually causes no symptoms.
- Even if high blood pressure does cause symptoms, the symptoms are usually mild and nonspecific (vague, or suggesting many different disorders).
- Thus, high blood pressure often is labeled "the silent killer."
- People who have high blood pressure typically don't know it until their blood pressure is measured.
Sometimes people with high blood pressure have the following symptoms:
- Blurred vision
People often do not seek medical care until they have symptoms arising from the organ damage caused by chronic (ongoing, long-term) high blood pressure. The following types of organ damage are commonly seen in chronic high blood pressure:
- Heart attack
- Heart failure
- Stroke or "mini stroke" (transient ischemic attack, TIA)
- Kidney failure
- Eye damage with loss of vision
- Peripheral arterial disease
- Outpouchings of the aorta, called aneurysms
About 1% of people with high blood pressure do not seek medical care until the high blood pressure is very severe, a condition known as malignant hypertension.
- In malignant hypertension, the diastolic blood pressure (the lower number) often exceeds 140 mm Hg.
- Malignant hypertension may be associated with headache, light-headedness, or nausea.
- This degree of high blood pressure requires emergency hospitalization and lowering of blood pressure to prevent brain hemorrhage or stroke.
It is of utmost importance to realize that high blood pressure can be unrecognized for years, causing no symptoms but causing progressive damage to the heart, other organs, and blood vessels. Regular eye exams can help uncover signs of systemic hypertension.
How is ocular hypertension treated?
If your eye doctor prescribes medicines to help in lowering the pressure inside your eye, properly applying the medication and complying with your doctor's instructions are very important. Not doing so could result in a further increase in intraocular pressure that can lead to optic nerve damage and permanent vision loss (ie, glaucoma).
How is systemic hypertension treated?
You and your health care provider have options for treating your high blood pressure.
- Many people can lower their blood pressure significantly with lifestyle changes, such as weight loss and exercise, but most still need medication to keep their blood pressure in the healthy range.
- Whichever therapy you choose, it is important to have your blood pressure checked regularly to make sure that your treatment is working.
- Uncontrolled high blood pressure is a leading cause of heart disease, heart attacks, heart failure, kidney failure, vision problems, and stroke.
Factors that can't be changed
- Age: The older you get, the greater the likelihood that you will develop high blood pressure, especially systolic, as your arteries get stiffer. This is largely due to arteriosclerosis, or "hardening of the arteries."
- Race: African Americans have high blood pressure more often than whites. They develop high blood pressure at a younger age and develop more severe complications sooner.
- Socioeconomic status: High blood pressure is also more common among the less educated and lower socioeconomic groups. Residents of the southeastern United States, both whites and blacks, are more likely to have high blood pressure than Americans from other regions.
- Family history (heredity): The tendency to have high blood pressure appears to run in families.
- Gender: Generally men have a greater likelihood of developing high blood pressure than women. This likelihood varies according to age and among various ethnic groups.
Factors that can be changed
- Overweight (obesity): Obesity is defined as having a body mass index (BMI) greater than 30 kg/m2. It is very closely related to high blood pressure. Medical professionals strongly recommend that all obese people with high blood pressure lose weight until they are within 15% of their healthy body weight. Your health care provider can help you calculate your BMI and healthy range of body weight.
- Sodium (salt) sensitivity: Some people have high sensitivity to sodium (salt), and their blood pressure goes up if they use salt. Reducing sodium intake tends to lower their blood pressure. Americans consume 10-15 times more sodium than they need. Fast foods and processed foods contain particularly high amounts of sodium. Many over-the-counter medicines, such as painkillers, also contain large amounts of sodium. Read labels to find out how much sodium is contained in food items. Avoid those with high sodium levels.
- Alcohol use: Drinking more than one to two drinks of alcohol per day tends to raise blood pressure in those who are sensitive to alcohol.
- Birth control pills (oral contraceptive use): Some women who take birth control pills develop high blood pressure.
- Lack of exercise (physical inactivity): A sedentary lifestyle contributes to the development of obesity and high blood pressure.
- Drugs: Certain drugs, such as amphetamines (stimulants), diet pills, and some pills used for cold and allergy symptoms, tend to raise blood pressure.
As body weight increases, the blood pressure rises.
- Obese people are two to six times more likely to develop high blood pressure than people whose weight is within a healthy range.
- Not only the degree of obesity is important, but also the manner in which the body accumulates extra fat. Some people gain weight around their belly (central obesity or "apple-shaped" people), while others store fat around their hips and thighs ("pear-shaped" people). "Apple-shaped" people tend to have greater health risks than "pear-shaped" people.