Blood Flow to the Eye
Chat Highlights
January 22, 2003

Norma Devine, Editor

On Wednesday, January 22, 2003, Dr. Rick Wilson, a glaucoma specialist at Wills, and the glaucoma chat group discussed "Blood Flow to the Eye."

Moderator:  Good evening, Dr. Wilson.  The topic tonight is "Blood Flow to the Eye."  Are you ready for the first question?

Dr. Rick Wilson:  I'm ready.

P:  Is there one big blood vessel that takes blood to the eye or a bunch of small ones?

Dr. Rick Wilson:  The ophthalmic artery brings blood to the eye, ending up in the central retinal artery, which supplies the retina and the top layer of the nerve on the inside of the eye.

P:  Is optic nerve damage caused by a lack of blood supply?

Dr. Rick Wilson:  The outer two-thirds of  the nerve is supplied by the short ciliary arteries, which usually number two to five, sometimes more.  There seems to be a strong vascular component, especially in normal-tension glaucoma.  I explain to patients that if the IOP (intraocular pressure) is high, the heart has difficulty pumping blood into the eye against the pressure in the eye.  If the eye pressure is normal, but atherosclerosis or spasm of the vessel to the eye inhibit blood flow, the same situation could result, that is, the heart would have difficulty getting blood to the eye.

P:  Are there any medications that can help the blood flow to the eye?

Dr. Rick Wilson:  Aspirin, medications that inhibit spasm of the vessels to the eye, and medications to raise systemic blood pressure all can help to increase circulation.  Coumadin obviously is a blood thinner that increases blood circulation.  

P:  Are you referring to children's aspirin (81 mg daily)?

Dr. Rick Wilson:  Yes.  In fact,  my doctor, a cardiologist, suggests just two to three baby aspirins a week.

P:  What medications inhibit spasm of the vessels to the eye? 

Dr. Rick Wilson:  Calcium channel blockers are the usual medications tried to inhibit vasospasm. Beta-blockers help in migraines.

P:  What techniques are used to image blood flow to the eye?

Dr. Rick Wilson:  The color Doppler can image the velocity of blood flow to the eye. It does a good job with the central retinal artery and vein, but the short posterior arteries, which are much more important, are just at the limits of this technology. We get sort of summary readings from each side of the nerve, but do not know how many arteries they represent.

P:  How is magnetic resonance angiography used?

Dr. Rick Wilson:  Magnetic resonance angiography can image the larger vessels going to the eye and any atherosclerotic plaques blocking the arteries.

P:  Could a high cholesterol count cause a decrease in the blood supply to the eye?

Dr. Rick Wilson:  Yes, through the build-up of plaque.

P:  What causes a disc hemorrhage?

Dr. Rick Wilson:  No one knows for sure. It may be a mechanical effect, that is, the disk tissue slowly dies and gets absorbed by the body. As the surface of the nerve falls posteriorly, the vessel is stretched past its breaking point and a small hemorrhage forms.

P:  Is optic nerve damage due to diminished blood supply?

Dr. Rick Wilson:  Glaucoma is a multi-factorial disease in which vascular factors seem to play a major role. A theory put forth by Flammer and others is that one risk factor alone leads to damage only if it is especially pronounced. The combination of two or more risk factors, such as a mildly increased IOP (intraocular pressure) together with nocturnal systemic hypotension or vasospasm, are much more likely to cause disease.

P:  What are some of the risk factors?

Dr. Rick Wilson:  Of the vascular risk factors,  arteriosclerosis, systemic hypertension, dyslipidemia, and diabetes represent weak risk factors. Vascular dysregulation (for example, systemic hypotension, local vasospasm, and aberrant autoregulation of blood flow in the optic nerve head and choroid) appears to be the major vascular risk factor for glaucoma.

P:  Wouldn't other parts of the head and body besides the eye show symptoms of interrupted blood flow?

Dr. Rick Wilson:  They seem to.  A study by Stroman showed more tiny strokes in the brains of some patients with normal-tension glaucoma.  These are without symptoms for the patient, but can be picked up by MRIs.

P:  In someone with low blood pressure and a high IOP, is Cosopt a good choice, even though it's a beta blocker, if it decreases IOP?

Dr. Rick Wilson:  In normal-tension glaucoma, there are theoretical disadvantages to the use of a beta blocker. A prostaglandin would possibly be a better choice, but the main therapeutic effect is to lower IOP and Cosopt does that well.  In the situation you ask about, Cosopt would be a good choice.

P:  I have low-normal blood pressure and IOP in the 18 to 22 mm Hg range.  One eye lost vision after maxillofacial surgery and an infection.  During that time, my blood pressure was about 30% higher than normal.  Could there have been a connection between some of those factors and the loss of vision? Could the infection have caused a spike in blood pressure, which in turn caused a spasm of the optic nerve?

Dr. Rick Wilson:  High blood pressure is protective for glaucoma over the short term, as more blood is pumped into the eye. It is only when narrowing of the arteries happens,  due to thickening of the vessel wall, and atherosclerosis occurs due to the high blood pressure, that it becomes a liability.

P:  What can be done if atherosclerotic plaques are found to be blocking the arteries?

Dr. Rick Wilson:  If the plaque is in the carotid artery, it can be removed.  In smaller or harder to reach areas, narrowing may be able to be dilated by a catheter with a balloon inserted through the artery to that area and the balloon inflated.  

P:  What causes local vasospasm of the optic nerve?

Dr. Rick Wilson:  We are not sure what causes "dysregulation," that is,  abnormal regulation of the muscles in the wall of the small arteries.  Migraine sufferers and patients with Raynaud's phenomenon are thought to be especially prone to vasospasm.

P:  Is that why it is thought there may be a connection between glaucoma and Alzheimer's disease, because of a lack of blood flow to the eye and the brain?

Dr. Rick Wilson:  I have not seen any convincing proof of that.  Alzheimer's seems to be caused by a build-up of material that disrupts the connections between neurons in the brain.

P:  What role does a family history of glaucoma play in situations where reduced blood flow seems to be a major causative factor?

Dr. Rick Wilson:  A family history of glaucoma increases lifetime risk by 10  times for sisters, brothers, and children. Low systemic blood pressure also increases risk.

P:  If a patient has had a history of heavy menstrual flow due to uterine fibroids leading to anemia, could that possibly cause damage to the optic nerve?  If so, would the progression of glaucoma be arrested if a hysterectomy corrected the condition?  

Dr. Rick Wilson:  In the past, severe anemia has been linked to glaucoma damage.  If there are no other risk factors, then the glaucoma damage would be arrested by curing the anemia.

P:  If blood flow is strongly correlated with glaucoma, wouldn't there be a relatively high prevalence of glaucoma in patients with diabetic retinopathy?

Dr. Rick Wilson:  Many studies do show an increase in the prevalence of glaucoma in diabetics.  Diabetes, however, is not a strong risk factor. 

P:  I regularly do weight training and cardiovascular workouts on a treadmill.  Does that aid blood flow?

Dr. Rick Wilson:  Yes,  and that also lowers IOP to some extent.

P:  How low would diastolic blood pressure need to be to cause a problem with blood flow to the eye?

Dr. Rick Wilson:  Diastolic blood pressures of 30 to 40 mm Hg are low enough to seriously compromise blood flow to the eye, especially if you lying down and IOPs are increased over being upright.

P:  If lying down causes a problem for glaucoma patients, should we sleep with our heads more elevated than normal?  

Dr. Rick Wilson:  Theoretically, that would lower intraocular pressure slightly.  However, a good night's sleep might be more helpful,  as higher blood pressure when lying down is presently not a proven risk factor.

P:  Soon after I was diagnosed with advanced normal-tension glaucoma, my glaucoma specialist sent me in for an MRI (or CAT scan) of my head and eyes.  What would he have been looking for?  I have been certified as normal, so that is good.

Dr. Rick Wilson:  He may have been worried that you had a tumor in your head pressing on your optic nerve, or he may just have been trying to protect himself medicolegally by doing a complete work-up.

P:  Is excessive reading detrimental to glaucoma patients?

Dr. Rick Wilson:  No, reading increases the tone of the muscle in the eye that pulls on the drain, mechanically opening the drain (trabecular meshwork).  So, if anything, reading would lower intraocular pressure slightly.

P:  If reading increases the tone of the muscle that pulls on the drain in the meshwork, aren't there special exercises for the eye that will enhance that muscle?

Dr. Rick Wilson:  Pencil pushups may do that.  But, again, that's  a theoretical help without proven long-term benefit.  

P:  What are pencil pushups?

Dr. Rick Wilson:  Holding a pencil midway between both eyes and about 18 inches away and bringing it up toward your face till both eyes can no longer focus on the pencil, and one eye drifts out.

P:  What do pulsing vessels at the back of an eye with an IOP of 30 mm Hg indicate?  Is low blood flow causing damage in this situation?

Dr. Rick Wilson:  It may indicate that the blood pressure in the vessels is lower than normal; hence they collapse at a lower level than they should.

P:  What can be done to improve blood pressure in those vessels in the eye? 

Dr. Rick Wilson:  Strict diets can actually shrink cholesterol plaques in ocular vessels.  A few medicines, and sometimes increased salt intake, may raise blood pressure back up into the normal range.

P:  We haven't mentioned any relation between fragile veins and blood flow yet, have we?

Dr. Rick Wilson:  Diabetics and the aged have fragile vessels, but I am not sure what you are referring to.

P:  You mentioned that glaucoma in near relatives increases the risk for glaucoma by a large factor.  Several near relatives of mine have glaucoma, but each has a different kind:  pigmentary, narrow angle, open angle, and normal-tension glaucoma.  Does that suggest to you that there is some common factor behind all glaucoma?

Dr. Rick Wilson:  That's interesting.  Pigmentary, open-angle glaucoma,  and normal-tension glaucoma may be related.  I doubt if the angle-closure glaucoma is related.

P:  If there's a lot of damage to the optic nerve, are the nerves more fragile and more likely to be damaged even at lower pressures?  Can anything be done to protect badly damaged nerves from more damage?

Dr. Rick Wilson:  Yes.  Keep the intraocular pressure even lower than normal, get plenty of exercise, follow a good diet,  don't smoke, and perhaps, with your doctor's agreement, take aspirin. 

End of highlights for January 22, 2003.

On January 29, Dr. Werner discussed "Staging Glaucoma" in the Chat room. Click here for highlights of that meeting.

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