Why hypertension can increase likelihood of glaucoma

The relationship between blood pressure and glaucoma is complicated. Experts in this report by SADE OGUNTOLA` say that a healthy lifestyle where blood pressure is normal is not only good for the heart but also the eyes in the prevention of vision loss due to glaucoma.

Everyone needs some blood pressure so that blood can get to all of the body’s organs. But how much is enough? How much is too much?  High blood pressure, also known as hypertension, is often called the “silent killer,” because it usually doesn’t have symptoms.

Doctors have known for a long time that blood pressure that is too high can cause problems. It points to a higher risk of having heart disease, kidney disease and stroke. But now, doctors know that if it is even a little too high, it could be a sign of possible changes in the blood vessels of the eye. And such problems with pressures in the eye can lead over time to vision loss, including glaucoma.

Glaucoma, the second leading cause of blindness in the world, is a condition that occurs when too much pressure builds up inside the eye. This excess pressure pushes back against blood trying to enter the eye resulting in vision loss.

In 2011, a review by the University of Michigan Health System of more than two million people aged 40 and older from 2001 to 2007 found that people with hypertension had a 17 per cent increased risk of developing open-angle glaucoma.

Among these people who had visited an eye care provider one or more times from 2001 to 2007, those with diabetes alone had a 35 per cent increased risk of developing open-angle glaucoma.  Also, there was a 48 per cent increased risk of developing open-angle glaucoma for people with both diabetes and hypertension.

“The older an individual gets, the more the chances of having hypertension. This is also true for open-angle glaucoma, which is a disease commoner in the older age group,” said Dr Tarela Sarimiye, a consultant ophthalmologist (Glaucoma Specialist) at the University College Hospital (UCH), Ibadan.

No doubt, there is a chance of hypertension and glaucoma coexisting in an individual. However, Dr Sarimiye said research has not been able to prove beyond any doubt that hypertension can cause glaucoma.

“Researches had shown to some extent that persons with hypertension, particularly, uncontrolled hypertension, have a slightly higher risk of developing primary open-angle glaucoma.  These are still in the early stages.

“These researches have only shown an association between hypertension and open-angle glaucoma. That does not translate to having glaucoma. More researches need to be done to ascertain this relationship,” he said.

Dr Sarimiye, however, stated that hypertension on its own also causes other eye conditions that lead to poor vision, especially hypertensive retinopathy, a condition that arises from high blood pressure affecting the back of the eye, the retina.

If hypertensive retinopathy is mild or moderate, there may be no symptoms. However, a severe form of hypertensive retinopathy may lead to headache and vision problems. It can be diagnosed through a routine eye check-up.

Worse still, lower blood pressure, what is medically termed hypotension, is also not good for the eye. He stated, however, that hypotension, which is low blood pressure, have been shown and well documented to cause and also result in the progression of glaucoma, he added.

According to him, “the heart pumps blood to every part of the body, including the eye. The force by which that blood is pumped and also the resistance at which it flows is what is calculated as blood pressure.

Sarimiye explained: “Where this pumping factor is low as in hypotension, the blood supply to the eye is also less. If the blood supply to the eye is also less, then what we call the perfusion pressure of the eye, which is simply the difference between the blood pressure and the eye pressure, is also less.

“So, the capacity by which those nutrients and oxygen get to the eye, especially the nerve, is less; and in such an environment, the risk of damage of the nerve by high pressure is higher, so such individuals may develop glaucoma more than others. That is also one way by which low blood pressure may further cause the progression of glaucoma.

“Also, the other way by which low blood pressure may cause glaucoma or even worsen glaucoma in patients who have hypertension is if the treatment for hypertension is too aggressive, it will tilt them to a hypotensive state. At that low blood pressure, it can also affect the way the eye is perfused and cause damage.

“That is why we advise our hypertensive patients who are even on medications and who also have glaucoma to discuss with their cardiologist that medication should be given usually in the mornings.

“Blood pressure fluctuates and it is usually lesser at night. So, if they take their blood pressure drug at night, it could even drop further down and that will tilt the person further to hypotension while asleep, whereas, for most people, the eye pressure is usually higher at night. Due to this disconnect or disequilibrium between the blood pressure and the eye pressure, the chances of having glaucoma and progression of glaucoma is higher.”

Dr Opeyemi Komolafe, a consultant ophthalmologist, Federal Medical Centre, Owo, said it is expected that hypertension will affect everything that blood flows into if it is not properly managed.

He said, “There will be changes in the blood vessels which may reduce perfusion of those organs. Now, the eye is not an isolated organ; it also receives blood supply and the association between hypertension and glaucoma has not been properly established by any studies.

“But there are some few studies that have said that systemic hypertension is a risk factor for open-angle glaucoma, but it actually cuts across all forms of glaucoma because the way hypertension affects glaucoma has to do with perfusion pressure.

“That is why people who have glaucoma and they also have hypertension when you are controlling their blood pressure, you also must be careful because if you drop the blood pressure too much, the eye will not get enough blood supply and that will not affect the eye again.”

However, Dr Komolafe said that although hypertension can affect the development of primary open-angle glaucoma, other risk factors, such as family history, high eye pressure, ageing and being nearsighted (myopic), have more of an effect than any specific systemic disease.

Experts in the field of ophthalmology are of the opinion that diabetic and hypertensive patients should get an eye check-up done every year. This is because they are more likely to experience vision impairment as compared to their healthy peers. If a person with diabetes has a history of ophthalmological problems, then the check-ups need to be more frequent.

Glaucoma is an umbrella term for a group of degenerative diseases of the optic nerve at the back of the eye, which can cause irreversible loss of a person’s field of vision and primary open-angle glaucoma is its most common form. Many are not aware they have the disease.

Vision loss from glaucoma occurs when the optic nerve is damaged. In most cases, elevated eye pressure, also called ocular hypertension, contributes to this damage. This causes a gradual loss of peripheral or side vision.

As the disease progresses, the field of vision gradually narrows, and blindness can result. Glaucoma has no early symptoms, and by the time people experience problems with their vision, many have a significant amount of optic nerve damage. However, if detected early, glaucoma usually can be controlled and serious vision loss prevented.

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