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Physicians who treat glaucoma have a problem. They see glaucoma one-way, and treat it another.
“Glaucoma is multifactorial, but in our treatment and thinking we are unifactorial, intraocular pressure,” said Louis Cantor, MD, professor and chair of ophthalmology and director of glaucoma at the Eugene and Marilyn Glick Eye Institute at Indiana University, Indianapolis. “IOP is the only glaucoma risk factor with strong evidence at the moment, but it doesn’t recognize everything. We all recognize that pressure doesn’t have to be elevated to have or to progress with glaucoma.”
There are clearly other factors at work, Dr. Cantor said during his Shaffer-Hetherington-Hoskins Lecture at Glaucoma 360. Increasing age and female sex increase risk for glaucoma, as do family history and race. So, probably, do hypertension, diabetes, cardiovascular disease myopia, long-term steroid or corticosteroid use and a prior eye injury. Behavioral risk factors, including exercise, smoking, BMI, alcohol and caffeine, may also influence the risk of glaucoma.
But a risk factor is an association with a particular outcome, not a cause. Separating risk factors for glaucoma from causal factors is difficult. Changing risk factors can be difficult, if not impossible. And in the practical world of glaucoma treatment, there is a whole host of risk factors that are recognized but not particularly important.
“A risk factor is only important if you can modify it,” Dr. Cantor said. “You can exercise and reduce that particular risk factor, but you can’t do anything about age, ethnicity, gender, or family history.”
Beyond admonitions to exercise, clinicians have few modifiable risk factors to work with in delaying the progression of glaucoma. One is blood pressure. Both hypertension and hypotension are associated the development and progression of glaucoma, although hypertension is by far the more common concern.
Increasing evidence suggests that not just blood pressure, but blood flow, is an important element. Disc hemorrhage, nocturnal vasospasm, and other blood flow-related factors are all associated with glaucoma. So are low ophthalmic arterial pressure and low ocular perfusion pressure.
“The evidence appears to be strong that vascular abnormalities are important in development and progression of glaucoma,” he said.
Interactions between vascular flow and glaucoma risk can be complicated by medications commonly prescribed to control blood pressure and other cardiovascular disease risk factors, Dr. Cantor noted. Calcium channel blockers and angiotensin-converting enzyme (ACE) inhibitors tend to increase ocular blood flow. Alpha-blockers can either increase or decrease ocular blood flow depending on the circumstances.
Beginning in the mid-1990s, studies have found that diastolic perfusion pressure (DPP) shows a strong correlation with glaucoma, Dr. Cantor noted. DPP is the diastolic blood pressure minus the IOP. Anything over 50 is considered normal, but multiple studies suggest that lower DPP is associated with increased risk for progression in glaucoma.
A growing body of evidence suggests that the lower the DPP, the higher the glaucoma risk. More definitive data could emerge later this year from the Indianapolis Glaucoma Progression Study, now in its fourth year.
Evidence to date and clinical experience suggest that clinicians should add two measures to the standard glaucoma visit, blood pressure and a calculated DPP, Dr. Cantor said. Both measures can directly affect treatment and patient outcomes.
A simple blood pressure reading may uncover unrecognized hypertension as well as over-treated hypertension. Patients with untreated hypertension can begin drug treatment and immediately reduce their glaucoma. Reducing hypertension can also help reduce risk for cardiovascular disease, renal disease, and other conditions.
Patients with hypotension as a result of over-treated hypertension may see similar benefits as medication is adjusted to achieve normotension.
Every patient who is on any anti-hypertensive medication gets one additional question regardless of actual blood pressure. Dr. Cantor asks when they take their blood pressure medication. It is a simple question that can have a profound effect on glaucoma.
Many patients take their blood pressure meds at night. Nighttime medication is a reasonable step for many patients, since blood pressure can drop in the hours following ingestion. Hypotension and the resulting syncope can be a nuisance during the daytime, possibly even a danger if a patient happens to be driving during a blood pressure dip.
But nocturnal hypotension is a recognized risk factor for glaucoma. Simply moving anti-hypertensive meds to daytime use may reduce the glaucoma risk by altering nocturnal hypotension patterns.
“This is not a complicated thing to do,” Dr. Cantor pointed out. “And it doesn’t require any sophisticated technology. Recognizing the potential impact of vascular flow abnormalities could prompt a change in your own treatment recommendations and it could spark a conversation with both the patient and the patient’s hypertension manager. We can go beyond IOP and improve care for our patients by ensuring that hypertension is not overtreated and avoiding nocturnal hypotension.”
‘The evidence appears to be strong that vascular abnormalities are important in development and progression of glaucoma.’
Louis Cantor, MD