Risk Factors for Glaucoma
April 18, 2007
Norma Devine, Editor
On Wednesday, April 18, 2007, Dr. Rick Wilson, a glaucoma specialist at Wills, and the glaucoma chat group discussed “Risk Factors for Glaucoma.”
Moderator: Tonight’s topic is “Risk Factors for Glaucoma”. Dr. Wilson, will you start by telling us what the most important risk factors are?
Dr. Rick Wilson: The most important risk factor for most people is intraocular pressure (IOP). Even in patients with normal-tension glaucoma (NTG), lowering IOP slows down loss or stops loss of vision if the IOP is lowered enough.
P: What is the difference between a risk factor and a symptom?
Dr. Rick Wilson: A risk factor is a characteristic of a person that puts him or her at increased risk of developing glaucoma. A symptom is something the patient evidences as a result of the disease.
P: What are the non-ocular risk factors for glaucoma?
Dr. Rick Wilson: A family history of glaucoma in a mother, father, sister, brother, or offspring increases the risk four to nine times. Someone older than 60 years of age has 7 times the risk of developing glaucoma as someone under age 40. There is also a 22% increase in relative risk every 10 years after age 60.
Moderator: Are there non-ocular risk factors, such as race or gender?
Dr. Rick Wilson: Gender does not seem to be a risk factor, although there are more women with glaucoma than men. That’s because glaucoma is age related, and older women outnumber older men.
Race is a serious risk factor. African-Americans have 3.4 times the risk of glaucoma as Caucasians. Caribbean Blacks have six times the risk, the disease occurs earlier in life, and it is more severe.
Dr. Rick Wilson: Here’s some information just off the press from Rohit Varma and the Los Angeles Latino Eye Study:
The risk for POAG (primary open-angle glaucoma) in Latinos is four times higher than it is in Whites. The risk of POAG is higher in those older than 50 years of age compared to younger Latinos. The increase in risk to this extent (four times) was not known until this study.
Latinos in the older age groups (70 years and older) have a 1.5 times higher risk of having POAG compared to African-Americans in the same age groups.
The risk of having POAG is three-fold higher in Latinos who have siblings with glaucoma compared to those without any family history of POAG.
Risk of having POAG is 1.5 times higher in Latinos with type 2 Diabetes mellitus than those without diabetes. This association with diabetes was not known until this study.
Risk of having POAG is higher in Latinos with myopia than those without.
P: What do you think about the following as risk factors for glaucoma: cold hands, migraine headache, sleep apnea, cardiac arrhythmia (e.g., atrial fibrillation), low blood pressure, and orthostatic hypotension?
Dr. Rick Wilson: Vasospastic disease, such as migraines and Raynaud’s syndrome (cold hands), is a risk factor for normal-tension glaucoma. Sleep apnea has been linked to glaucoma in at least one study, but not all. Arrhythmias can also lead to glaucoma damage if the blood flow to the eye is affected. Low blood pressure, especially diastolic, is a risk factor for glaucoma.
P: Have the risk factors changed any over the last few decades?
Dr. Rick Wilson: Thyroid disease was a risk factor, then it wasn’t. The latest study I saw said it was a weak risk factor. Diabetes was once considered a risk factor. The Baltimore Eye Study, however, found diabetes was a risk factor for elevated IOP, but not necessarily nerve damage and glaucoma. The Los Angeles Latino Eye Study did find diabetes a risk factor in that segment of society.
P: Do any medications have the potential to cause glaucoma?
Dr. Rick Wilson: Steroids, especially topically, but also systemically, can cause an IOP rise. In patients with narrow and occludable angles, medications like cold medications that cause dilation of the pupils can cause angle-closure glaucoma.
Topiramate (Topamax), an anti-epileptic and anti-depressant, as well as other sulfonamides, such as acetazolamide, can cause bilateral fluid build-up between the layers of the eye and cause angle-closure glaucoma.
P: How about corneal flatness, flexibility, and thickness?
Dr. Rick Wilson: We haven’t really talked about the ocular risk factors, which we can do now. Central corneal thickness (CCT) carries an 81% increase in risk for every 40 microns thinner than the norm.
Ocular trauma, corneal endothelial dystrophy (Fuchs’ dystrophy), pseudoexfoliation, pigment dispersion, and a history of a retinal detachment or central retinal vein occlusion are risk factors. Myopia or near-sightedness was a weak risk factor in a large Australian study.
P: Do you have an opinion on corneal hyteresis (CH) as a risk factor for glaucoma? One study indicates low CH is a greater risk factor than thin CCT. I would like to know your opinion because CH is a new measurement.
Dr. Rick Wilson: I think we are just now unraveling the factors that go into the cornea’s resistance to the applanation tonometer (the prism used with the blue light to take pressure in the eye by flattening a circle with a diameter of 3.06 mm). Some of those factors seem to be related to the doctor getting an artificially inaccurate pressure measurement. Some may also be related in a more fundamental way to the support structure of the eye, which makes the eye more susceptible to glaucoma damage. I think it is too early to try to determine which factors fall into which category or are unrelated.
P: Is corneal thickness hereditary?
Dr. Rick Wilson: I don’t know enough to comment definitely. There may be a tendency, but my patients have been all over the board compared to at least one of their parents.
P: Is there clinical trial evidence showing how much the IOP needs to be lowered to stop progression in NTG?
Dr. Rick Wilson: The Normal Tension Glaucoma Treatment Trial (NTGTT) reported that patients in whom a 30% decrease in IOP was achieved, 20% showed visual field progression at five years, with an average IOP of 11 mm Hg. Sixty percent showed visual field progression at five years, with an average IOP of 16 mm Hg.
Patients with demonstrated susceptibility to normal IOPs may need IOPs in the single digits to stop progression. Most surgeons try to lower IOP about 40% in NTG patients who have shown progression.
P: I am a 60-year-old male diagnosed with NTG. How common is that?
Dr. Rick Wilson: It’s uncommon, as most NTG patients are older, but you are not out of the range where we see it. Make sure your blood pressure (BP) is not too low.
P: Do you know of any association between a deviated septum and elevated intraocular pressure or optic nerve damage?
Dr. Rick Wilson: No, I don’t.
P: Is vascular disease a risk factor for glaucoma? If so, how?
Dr. Rick Wilson: We talked about blood pressure that is too low. It has been thought that chronic hypertension, especially if treated, was a risk factor. Patients with blood that is too thick, possibly related to too many blood cells or too much protein, seem to be at increased risk.
We mentioned vasospastic disease. It is thought that glaucoma patients do not regulate the blood flow to the optic nerve as accurately as normal patients. There may be a lack of autoregulation of muscle tone in the vessel walls, etc., in response to a variety of stimuli and stress.
P: What is the consensus on computer usage as a cause of myopia or glaucoma?
Dr. Rick Wilson: There may be a little connection to myopia, as there is to reading, especially up close. There seems to be no connection whatsoever to glaucoma.
P: I would like to know the best way to calculate ocular or retinal perfusion pressure myself. This is related to low nocturnal BP as a risk factor. I can monitor my own BP at night, as well as my own IOP. What is the right formula for determining ocular perfusion pressure in that situation? Any comment on thresholds?
Dr. Rick Wilson: How do you monitor your IOP? It is difficult to do without a skilled assistant. The key factor is how close the eye pressure is to the diastolic pressure. Clearly, if they are equal, there is no blood flow into the eye, and the closer they are, the slower is the blood flow.
P: In the daytime, my IOP is usually under 15 mm Hg (and most often around 12 mm Hg). However, at night my IOP can approach 20 mm Hg. My diastolic BP can drop to 50 mm HG at night (from around 70-75 mm Hg during the day). I measure my IOP with a couple of different professional tonometers, and I measure my BP with an Omron home electronic unit (non-professional).
Dr. Rick Wilson: Diastolic BP of 50 mm Hg is certainly of concern when your eye pressure is at the highest of the 24 hours.
P: What range of BP would be considered too low as far as adversely affecting glaucoma?
Dr. Rick Wilson: I worry about diastolic pressure (the lower pressure) less than 60 mm Hg, especially if the IOP is in the 20’s. Unfortunately, many people are “dippers”. There is a diurnal curve of blood pressure similar to the diurnal curve of intraocular pressure. As with eye (intraocular) pressure, the blood pressure is at its lowest during the early morning hours.
In patients with hypertension, the lowest pressures are between 2:00 and 4:00 a.m. Two-thirds of the normal population will have a blood pressure drop of greater than 10% during that period. Patients with systemic hypertension usually evidence a much greater swing in systolic and diastolic blood pressure, with an average of a 26% drop from day to night. Those patients are called “dippers”.
Hypertensives treated with beta blockers can have diastolic blood pressures during sleep of 50 mmHg or less, and rarely down to 30 mmHg or less. An abnormally deep dip may compromise local vascular supply. Dr. Stephen Drance found a much higher incidence of POAG progression among “dippers”.
P: You mentioned “blood too thick.” Can blood become too thick from chronic inflammation (e.g., too many white blood cells making the blood thicker)?
Dr. Rick Wilson: I think it can with leukemia, but not with inflammation.
P: Given the studies showing the beneficial effects of exercise on IOP, wouldn’t you consider a sedentary lifestyle a risk factor for progression?
Dr. Rick Wilson: I do, and also obesity, although there is less agreement on the latter.
P: Are there any eye exercises that can strengthen or improve blood circulation to the optic nerve?
Dr. Rick Wilson: Not eye exercises, but systemic exercises can promote circulation throughout the body, including the eyes.
P: Can hanging upside down potentially cause damage to the optic nerve?
Dr. Rick Wilson: Position is important. Some patients have an exaggerated increase in IOP when lying down.
P: Would you please elaborate on that?
Dr. Rick Wilson: Since the eye pressure over the short term is equal to the venous blood pressure around the eye, raising the blood pressure by having all the blood in the body push toward the head causes a big increase in eye pressure. Weightlessness also causes an increase in eye pressure. (Watch out on the space station!)
When people lie down, their IOPs increase. During sleep, it can be even higher. IOP is especially high upon awakening in the early morning.
P: Does an unsuccessful laser surgery (trabeculoplasty) put a glaucoma patient at increased risk of visual field progression?
Dr. Rick Wilson: Not if it hasn’t caused a rise in IOP. But it does move the patient closer to cutting surgery.
Moderator: Thank you, Dr. Wilson. Goodnight.