Blood Flow & Glaucoma

Blood Flow & Glaucoma
Chat Highlights
February 27, 2002
Norma Devine, Editor

On Wednesday, February 27, 2002, Dr. Elliot Werner, a glaucoma specialist at Wills, and the glaucoma chat group discussed “Blood Flow & Glaucoma.”

Moderator: Good evening, Dr. Werner.

Dr. Elliot Werner: Hello, everybody. Let me warn you right off the bat. I am no expert on the subject of blood flow.

Moderator: Thanks for the warning, Doctor Werner. Would you prefer to discuss a different topic?

Dr. Elliot Werner: No. I’ll do my best.

P: Whatever you tell us will be helpful.

Dr. Elliot Werner: I’ll start. Blood flow refers to the quality and quantity of the circulation of blood through the eye.

Moderator: Lutein was touted as being good, I think, for macular degeneration or something else. Might it have some beneficial effect relating to blood flow and glaucoma?

Dr. Elliot Werner: Not that I’m aware of.

Moderator: Is there any test that can visualize blood flow in the eye?

Dr. Elliot Werner: There are some tests that can measure blood flow in different parts of the eye, but they are all relatively crude.

P: It seems that among the many causes of glaucoma, weakness in the ocular vascular system is a main suspect, at least for normal-tension glaucoma (NTG). Is that as likely as it sounds to me?

Dr. Elliot Werner: There is a lot of evidence for decreased blood flow in normal-tension glaucoma, as well as for other forms of glaucoma. There is very little evidence that this is causative. It might be the result, rather than the cause. There is also no good evidence that altering blood flow affects the course and outcome of glaucoma.

P: I’d like to know if caffeine constricts blood vessels.

Dr. Elliot Werner: I think caffeine constricts blood vessels and reduces blood flow.

P: If caffeine constricts blood vessels and reduces blood flow, how does that affect glaucoma? In the morning, coffee seems to help open my eyes and lungs and sinuses. I also suffer with blepharitis.

Dr. Elliot Werner: Studies on caffeine and coffee drinking have not shown any effect, one way or the other, on glaucoma. So don’t worry about the coffee.

P: It seems no one is really doing much about the connection between blood flow and glaucoma. Doctors just treat the IOP (intraocular pressure) in the eye itself. If they really thought there was a connection, wouldn’t they be doing something about it, especially for people with no real indicators of why they have glaucoma?

Dr. Elliot Werner: There is no good way to alter blood flow to the eye, and no evidence that it helps anyway.

P: How does high blood pressure affect blood flow in glaucoma, and the medications that are used to control it?

Dr. Elliot Werner: High blood pressure can have two effects. In the absence of any other vascular disease, high blood pressure increases ocular blood flow. If the high blood pressure has caused damage to blood vessels — as it often does — it may reduce blood flow. Medications to treat blood pressure can reduce ocular blood flow if the blood pressure is lowered too much.

Moderator: Does blood circulate all over the eye (e.g., the iris, lens, cornea, optic nerve)? If the eye or a part of it does not get enough blood flow, will it be unhealthy?

Dr. Elliot Werner: Blood does not flow through the transparent parts of the eye, or else they would not be transparent. Otherwise, all the other parts of the eye have blood just like other parts of the body.

Moderator: Can poor circulation to the eye cause pain in the eye?

Dr. Elliot Werner: Yes. Poor blood flow to the whole eye is called ocular ischemic syndrome, and can be quite painful.

P: My general practitioner said he could feel a pulse in my ankle, which indicates that I have good blood flow to the extremities. Would that also mean good blood flow to the eye?

Dr. Elliot Werner: Not necessarily. They are completely different vascular beds and do not always relate.

P: Could you explain “vascular beds?”

Dr. Elliot Werner: Vascular bed refers to the general part of the body supplied by a particular part of the vascular system (blood vessels). Usually a vascular bed derives from a single terminal artery.

P: Although there are no direct clinical results yet, isn’t ischemia a key reason for death of the nerves and shouldn’t improved blood flow limit the damage?

Dr. Elliot Werner: You would think so, but there is no evidence for it.

P: Is there a blood pressure that you consider dangerously low for a glaucoma patient?

Dr. Elliot Werner: There is good evidence that chronic low blood pressure is associated with worse glaucoma. Blood pressure below 100 mm Hg systolic and 60 mm Hg diastolic can be dangerous.

P: I watched the blood pressure machine before my surgery. I thought my blood pressure would increase because I was nervous. But I saw it was only 80 over 41 mm Hg! How could I increase my blood pressure?

Dr. Elliot Werner: I don’t know. There is no good way to raise blood pressure on a chronic basis without excessive risk from dangerous drugs. Try eating a lot of salt. Check with your doctor.

P: Sometimes when I stand up, my vision dims. Does that just affect my brain or does it also affect blood flow and intraocular pressure?

Dr. Elliot Werner: Vision dimming with changing posture can be a sign of poor blood flow to either the eye or the brain and should be evaluated.

P: How is that done?

Dr. Elliot Werner: A variety of tests are available, including color orbital Doppler, MRA and non-invasive carotid flow studies.

P: Which is more important, the velocity of the blood flow or the total quantity? It seems that if the arteries are constricted, you get a higher velocity. It’s very confusing.

Dr. Elliot Werner: This is a very complex and poorly understood area. The optic nerve in glaucoma dies by a mechanism called apoptosis. Apoptosis can be provoked by many different types of injuries, including poor blood flow, as well as many others. “Flow” refers to the total amount of blood flowing through. “Flow rate” refers to the speed. Flow rate is much easier to measure, and most studies relate to velocity or flow rate rather than to total flow.

P: This may be a dumb question, but would increasing carotid artery flow automatically increase blood flow to the optic nerve?

Dr. Elliot Werner: There are no dumb questions; only dumb answers. There is no doubt that unblocking a blocked carotid artery will increase blood flow to the eye. Whether or not that will do any good is another issue.

P: I have been at the University of Indiana facility with Dr. Alon Harris to measure blood flow with three types of measuring devices. All three verified that my ocular vascular system is on the low side of what they consider normal. We have added dorzolamide to my meds to see if that will improve blood flow.

Dr. Elliot Werner: A few small studies have indicated that dorzolamide increases blood flow, independent of intraocular pressure (IOP). As always, these are small tests, so it is only important for each patient, I guess. Most drugs that lower IOP also increase blood flow, but they do so by lowering the IOP, not by affecting the blood vessels directly.

P: I am working on a theory that describes my normal-tension glaucoma as caused by very myopic eyes that are at the extreme of length (over 28 mm). The theory is that the blood supply simply is stretched too thin with such large eyes, so anything I can do to improve blood flow should be helpful. You seem to be doubtful about the effects of improving blood flow on glaucoma. For those of us with normal-tension glaucoma, what else can we do once our IOP is at 13 to 14 mm Hg?

Dr. Elliot Werner: I’m not doubtful about increased blood flow probably being helpful. The problem is there is no good way to do it that has been shown to work and affect the course of glaucoma.

Moderator: Is any research being done to get better vascular images of the eye?

Dr. Elliot Werner: There is a lot of research in this area. Unfortunately, it is outside my area of research interest, so I am not very knowledgeable about that.

P: Do you know of any studies showing that patients with low blood pressure or thick blood are less likely to have successful surgery?

Dr. Elliot Werner: I don’t know of anything about low blood pressure, but people with a variety of blood diseases are at risk for hemorrhage after eye surgery.

P: Does ginkgo biloba increase blood flow?

Dr. Elliot Werner: There is some (not great) evidence that ginko slows the progression of glaucoma. I’m not aware, off the top of my head, of studies on blood flow.

Moderator: Is poor blood circulation hereditary?

Dr. Elliot Werner: It’s not known for sure, but it (like most things) probably has a strong genetic component.

P: Is there at least a consensus that vasodilation improves blood flow, or is that still under investigation, too? Does it matter whether it’s endothelium-dependent or -independent vasodilation? (These can be modulated separately.)

Dr. Elliot Werner: Vasodilation increases blood flow. That’s why our skin feels warm when we blush, and cold when we’re afraid. Whether or not the vasodilation increase in blood flow helps a particular disease is another matter. Vasodilation also lowers blood pressure, which can be harmful.

P: I have a lot of eye pain. Imitrex often helps. Does Imitrex dilate the blood vessels?

Dr. Elliot Werner: Imitrex, I think, is a treatment for migraine headache. If it is relieving your pain, you are probably having migraine headaches.

P: Thanks, Dr. Werner. Very interesting chat. As usual, I learned some more.

Dr. Elliot Werner: It’s 9:30 p.m. EST, so I’m going to bed. See you all March 27th.
End of highlights for February 27, 2002.


About the Author:

The Glaucoma Service Foundation’s mission is to preserve or enhance the health of all people with glaucoma and to provide a model of medical care by supporting the educational and research efforts of the physicians on the Wills Eye Institute Glaucoma Service, the largest glaucoma diagnosis and treatment center in the country.
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