Blood Flow and Glaucoma
Chat Highlights – June 4, 2014
Guest Speaker – Dr. Anand Mantravadi
Lorraine Miller – Editor, Chat Topic Researcher
Moderator: Welcome, Dr. Mantravadi. Thank you for joining us for our chat tonight on “Blood Flow and Glaucoma.” Your expertise is always appreciated!
P: Good evening, Doctor. Would you please explain systemic blood flow and optic nerve head blood flow?
Dr. Mantravadi: Perfusion pressure of the eye is the difference between blood pressure (BP) and intraocular pressure (IOP). It is important for the physician to ask the patient if there is a history of low BP particularly at night in patients where the diagnosis of normal tension glaucoma is being considered. I think knowing about a patient’s general BP control and prior diagnosis of hypertension or hypotension is very important. The value of knowing the actual perfusion pressure is not known. The perfusion pressure will likely be variable given that BP varies, IOP varies, and the measurement taken in an internist or ophthalmologist’s office is probably a small window of the overall trend in perfusion pressure.
P: Would you also explain how blood flows through the eyes?
Dr. Mantravadi: Blood is sent to the eyeball from the heart. The terminal arteries and arterioles off the carotid artery feed the eye and perfuse the tissues. The veins will cycle this blood through the venous return system.
P: Should it be a standard practice for glaucoma patients to be asked about blood pressure or have their blood pressure taken at every office visit?
Dr. Mantravadi: We routinely will inquire about blood pressure for several reasons. Low BP or diastolic BP has been associated with some types of glaucoma. Other studies have found an association between high BP with some types of glaucoma. High BP or hypertension can negatively impact the small blood vessels, arteries, and veins that feed the eye and may also contribute to secondary types of glaucoma. For those reasons, we do make it a practice to ask our glaucoma patients about their blood pressure.
P: What is the relationship between blood flow and the eyes?
Dr. Mantravadi: Blood flow is important to the health of the eyes. General good vascular health and cardiovascular fitness is very important to promote good ocular nutrition and health.
P: There are mechanical and vascular theories that exist and both could be responsible for glaucoma. Would you explain them as they relate to glaucoma?
Dr. Mantravadi: Mechanical theories for glaucoma include the concept that increased eye pressure can cause stretching of the structural support system for the optic nerve causing cell damage and ultimately functional visual loss. The vascular theory supports glaucoma neuropathy as a consequence of insufficient blood flow into the eye due to high IOP or insufficient perfusion of the ocular tissues.
P: Are there treatment or prognosis implications if primary glaucoma has been diagnosed and the patient has fairly low blood pressure?
Dr. Mantravadi: Although there’s evidence that low diastolic or perfusion pressure may have some role in progressive glaucoma, there is no scientific rationale to increase BP as this may have untoward consequences. Lowering intraocular pressure can increase perfusion pressure to the eye.
P: What equipment is used to measure blood flow to the eyes?
Dr. Mantravadi: This is not done routinely. Ultrasound or Doppler studies can ascertain ocular blood flow.
P: What level, frequency, and type of exercise could help improve blood flow to the eye?
Dr. Mantravadi: Any mode of exercise that enhances cardiovascular fitness will promote good ocular blood flow.
P: Does a decrease in blood flow occur in all forms of glaucoma or only in primary open-angle glaucoma (POAG) and normal tension glaucoma (NTG)?
Dr. Mantravadi: A decrease in blood flow does not occur in all forms of glaucoma. There is much to learn regarding the BP and glaucoma relationship. As I mentioned earlier, low diastolic BP is a possible risk factor for glaucoma but may not always be the case in POAG and NTG.
P: Are there visual indirect signs of decreased blood flow that our glaucoma specialist views in our eyes?
Dr. Mantravadi: There are no specific indirect signs for merely low perfusion pressure. There may be signs of arteriolar hardening or narrowing in high BP states.
P: How is optic nerve head blood flow autoregulated? Does glaucoma affect this regulation process?
Dr. Mantravadi: It is thought that abnormalities in autoregulation can result from atherosclerosis or vascopasticdisease. The abnormalities in autoregulation may contribute to lack of oxygen, tissue ischemia and participate in optic nerve damage. This is part of the vascular theory that could be responsible for glaucoma.
P: Why does a reduction of ocular blood flow precede glaucomatous damage?
Dr. Mantravadi: I don’t think we know the answer to that. If one ascribes to a vascular component of glaucomatous neuropathy, lack of blood flow induces ischemic injury that can lead to cell damage or loss characteristic of glaucoma but the precise pathway is unclear.
Moderator: We are out of time. We would like to extend our appreciation to Dr. Mantravadi for joining us tonight and sharing his wealth of knowledge. We also would like to thank our chatters for their participation in tonight’s chat. Good night!