Glaucoma Risk Factors
Chat Highlights
December 2, 2009

On Wednesday, December 2, 2009, Dr. Michael Pro, a glaucoma specialist at Wills, and the glaucoma chat group discussed "Glaucoma Risk Factors".

Moderator: Welcome. Tonight's Topic is Risk Factors for Glaucoma. Dr. Pro, what is a risk factor?

Dr. Pro: A risk factor is some characteristic that increases one's risk of developing glaucoma or of having pre-existing glaucoma get worse.

P: How many risk factors do glaucoma patients usually possess when diagnosed with glaucoma?

Dr. Pro: Well, usually at least one. Let's begin by saying that various studies have described different risk factors. It is generally agreed that IOP higher than normal and increasing age are major risk factors in most studies. The Ocular Hypertension Treatment Study (OHTS) went on to find three other major risk factors: thin corneas, visual field performance and optic nerve characteristics.

So, when I said that most glaucoma patients have at least one risk factor at diagnosis, the most common characteristic is that persons with glaucoma are usually older (but not always!).

Let's talk about other risk factors that have been found in some studies and not in others; we'll call them minor risk factors. These include (but are not limited to) high blood pressure, diabetes, auto-immune diseases, myopia, family history, and other eye conditions.

P: What are the risk factors that can be controlled or influenced by the patient?

Dr. Pro: You could manage your blood pressure and control your diabetes, which could help prevent the development of glaucoma. Some studies have found that weight loss may help lower the IOP, as would regular exercise, so lifestyle modification may reduce your risk of developing glaucoma.

P: What is visual field (VF) performance?

Dr. Pro: There is certain statistics that are generated when you perform a visual field test. Certain visual field defects may indicate early glaucoma and people with these defects are more likely to develop full blown glaucoma.

P: How thin do corneas have to be to be considered a risk factor?

Dr. Pro: The OHTS papers report a corneal thickness less than 555 microns as putting a patient at greater risk to develop glaucoma, but we generally consider a cornea around 500 microns or less as being really thin, and probably even greater risk.

Moderator: So one with thin corneas is more likely to develop glaucoma?

Dr. Pro: Yes, and we are not entirely sure why. It may be partially due to the fact that with a thin cornea, the "true pressure" is slightly higher, but the study found that the risk due to thin corneas was independent of IOP, so it may be true that people with thin corneas have nerves more susceptible to develop glaucoma for another reason.

P: Is corneal thickness hereditary?

Dr. Pro: Yes, to some degree, as are many of your eye characteristics.

P: Do the ethnic heritages mentioned in the risk factors, African American and Mexican American, have a structural defect of the eye that increases their risk for the disease?

Dr. Pro: That same study (OHTS) did not find race to be a risk factor, but others have. One finding is that persons of African origin are more likely to have thin corneas. But, I should be very clear that for whatever reason, African Americans are as much as four times more likely to develop glaucoma than whites, and are more likely to have more advanced disease at diagnosis. Hispanics also seem to have a higher incidence of glaucoma. These groups really need to be reached better by our medical system, to find people at risk of developing glaucoma before the disease is advanced.

P: If a family has a history of glaucoma diagnosed by 40 years of age, would a structural problem passed on through the generations be the cause?

Dr. Pro: That is not early enough to really be considered juvenile glaucoma. It is certainly possible that glaucoma is at least partially due to genetic factors, like other diseases, so you may be more susceptible to develop glaucoma due to your genes inherited from your parents, but poorly understood environmental factors may cause you to go on to develop disease. Childhood glaucoma is often strongly genetic and siblings need to be screened.

P: Is having a sibling with glaucoma more of a risk factor than having a parent with glaucoma, and if so, why?

Dr. Pro: No, studies have found that a first degree relative with glaucoma puts you at greater risk. Having a sibling with glaucoma does not put you at greater risk.

P: Is corticosteroid use a potential risk factor?

Dr. Pro: Yes, steroids can increase the IOP and this can increase the risk of developing glaucoma.

P: Have studies been done that seek to correlate health factors such as weight, blood pressure, diabetes, etc. within race and glaucoma to determine how much is racial and how much is not?

Dr. Pro: Yes, for instance, the OHTS (ocular hypertension treatment study) did look at those factors and found that race as a risk factor fell out. But any study has problems, for instance OHTS found that diabetes was PROTECTIVE. This made no sense—researchers took a hard look at the data and felt that the way that the study asked about diabetes may have skewed the data. Questions about race can also be tricky.

P: If you have a shot of Kenelog which triggers glaucoma for the first time at 50 years old, is this considered genetic? I do have an autoimmune disorder, ankylosing spondylitis.

Dr. Pro: I wouldn't say that this indicates a genetic issue. As I said above, certain individuals may be at greater risk for developing glaucoma, and we don't always understand why. Steroid eye injections can elevate the IOP.

P: Are there any genetic tests that accurately predict glaucoma?

Dr. Pro: The most recent finding with this is the discovery of the genetic markers for pseudo exfoliation syndrome, which is a condition that puts individuals at much greater risk of developing glaucoma. There is no commercially available blood test, but I could imagine tests in the future that would look at certain markers. Ultimately, for now, detection of glaucoma is best accomplished by routine eye care.

P: Are migraines a risk factor for POAG?

Dr. Pro: Migraines are usually discussed as a risk factor for normal tension glaucoma and may be a marker for an abnormality in normal blood flow to the optic nerve.

P: Do a higher proportion of normal tension glaucoma patients have cardiovascular disease compared to POAG patients?

Dr. Pro: Great question. I don't think so, but I can't cite any specific article.

P: Could a large amount of blood loss where a transfusion is required be a risk factor for any of the glaucoma’s because blood flow to the eye was compromised?

Dr. Pro: Yes and we also worry about major surgery where the blood pressure is very low for an extended period of time.

P: Is there a particular eye shape like those of East Asian and Inuit ethnicity that is an indicator for closed-angle glaucoma?

Dr. Pro: Inuit in particular has been found to have a narrower anterior chamber. East Asians were also thought to have this as well, but some recent research shows that the iris contour and lens position may play a role in increasing their risk of developing angle closure.

P: Are children subject to the same risk factors as adults? In your experience, if they have risk factors such as high pressure, myopia or pale nerves, do they develop glaucoma at a greater rate than adults?

Dr. Pro: A pale nerve is pathologic, and may indicate a problem other than glaucoma. High pressure is especially worrisome in a child because they do not usually have high IOP. Conversely children do not usually develop glaucoma at normal IOPs. In fact infantile glaucoma can present very dramatically with a blue-discolored and enlarged cornea. In some respects this is good because babies can not tell you that something is wrong.

P: Is most of the blindness caused by glaucoma seen in patients that were diagnosed before the age of 40 or are older patients at equal risk for blindness?

Dr. Pro: Risk of blindness depends on the status of the nerve at diagnosis, so would be age independent.

Moderator: Well thank you Dr Pro. That's all the time we have for this evening. It was an interesting and informative chat.

Dr. Pro: You're welcome. Goodnight.

On December 16, Dr. Pro discussed "Glaucoma Research" in the Chat room. Click here for highlights of that meeting.

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