Glaucoma and blood pressure have a complex relationship. Both low and high blood pressure may increase the risk of incidence, as well as progression of glaucoma.
High blood pressure may increase eye pressure. On the other hand, low blood pressure decreases the blood flow to the optic nerve. Both of these are not good for the health of the optic nerve, and consequently, impact glaucoma adversely.
Glaucoma and High Blood Pressure
Various researchers have had conflicting results, when studying the relationship between high blood pressure and glaucoma. However, what we do know for a fact is that an increase in blood pressure results in increased eye pressure. This is probably because high blood pressure increases the amount of fluid the eye produces. Alternatively, this may be because high blood pressure decreases the amount of fluid drained out of the eye.
Despite this, remember that the effects of increasing blood pressure is not very large. That is, a blood pressure increase by 10 mmHg only raises the eye pressure by approximately 0.26 mmHg.
More importantly, remember that high blood pressure can impact eye health adversely by more than one mechanism. Of course, it can increase the eye pressure as explained above. In addition to that, high blood pressure can damage the retina and result in hypertensive retinopathy. This condition is may also impact your vision adversely.
Glaucoma and Low Blood Pressure
On the other hand, contrary to popular opinion, low blood pressure is also not good for the optic nerve health. In fact, it can be a risk factor for developing glaucoma.
To understand this, you must understand the concept of ocular perfusion pressure. This is the difference between blood pressure and eye pressure. The perfusion pressure determines the amount of blood reaching the blood flow, and consequently, its nourishment.
Therefore, both, patients who have low blood pressure, and those with high blood pressure who are over treated with medications, are at a higher risk of glaucoma progression.
What happens at night?
Another important thing to remember is your night time blood pressure. Normally, our blood pressure naturally dips at night. At the same time, we know that eye pressure increases at night, and peaks at around 2AM to 4AM. Understandably, the blood flow to the optic nerve can therefore be compromised at night. This results in glaucoma progression and visual field loss.
For this reason, in addition to doing a 24 hour eye pressure monitoring, your eye doctor may advise an a 24 hour blood pressure monitoring also.
Medication for blood pressure
Beta blockers are used to decrease both, eye pressure and blood pressure. The former is in the form of eye drops, while the latter is an oral medication. However, in both forms, a common side effect of beta-blockers is decreased heart rate.
Therefore, simultaneous use of both a systemic beta-blocker and a beta-blocker eye drop can result in side effects.
Moreover, if you are already taking beta blockers orally, the beta blocker eye drops (most commonly used, timolol) will not be as effective in lowering eye pressure. Also, beta blockers should be avoided at night to prevent night time dips in blood pressure, especially in glaucoma patients.
Calcium channel blockers and angiotensin converting enzyme inhibitors decrease blood pressure, without affecting eye pressure. This reduces ocular perfusion pressure, and increases the risk of glaucoma. Therefore, beta blockers are the preferred class of drugs for treatment of hypertension in patients with glaucoma.
Things to discuss with your doctor
Your primary care physician who is treating your blood pressure must know you have glaucoma. Similarly, you must discuss with your treating ophthalmologist about your blood pressure. This would include details of whether you have high blood pressure, the duration of disease, and if you are taking blood pressure medications. The latter is especially important if you are using systemic (oral) beta-blockers.
High blood pressure can lead to chronic kidney disease, which requires dialysis. The blood pressure fluctuates and dips during dialysis, leading to low ocular perfusion pressure. This can lead to glaucoma progression. So, if you need dialysis, you must discuss this with both, your nephrologist, and your eye doctor.
So what’s the verdict?
- Both high and low blood pressures can damage the optic nerve.
- As always, moderation is key. Avoid extremes in blood pressure, so that it is not too low and not too high.
- Discuss your high blood pressure and your medication history with your eye doctor. Tell your primary doctor you have glaucoma, or are at risk.
- Remember, night time dips in blood pressure must be avoided.
- Similarly, beta blocker eye drops must be avoided, if you are already using an oral beta blocker for your high blood pressure.
