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Identifying glaucoma risk factors beyond IOP

Issue: April 2005

ByBob Kronemyer

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Apart from assessing intraocular pressure, cup-to-disc ratio and visual fields, a number of other red flags are associated with an increased risk for glaucoma. These include gender, migraine, ethnicity, diabetes and central corneal thickness.

History of migraines

“Migraine headache appears to be a vasospastic disorder,” said Leo P. Semes, OD, FAAO, an associate professor of optometry at the University of Alabama at Birmingham School of Optometry. “Migraine, along with a condition such as Raynaud’s phenomenon, probably suggests the presence of some contributing auto-dysregulation disorder.”

One of the characteristic clinical signs of Raynaud’s phenomenon is cold hands and feet. “Therefore, I always pay attention to the temperature of the hand when I shake a patient’s hand. Is it warm or cold?” Dr. Semes, a Primary Care Optometry News Editorial Board member, said in an interview. “Patients who describe cold hands and feet may be unusually sensitive to cold, for example.”

A history of migraine headache can typically be gleaned from the patient’s history or medications. “Some reports suggest that patients with migraine may, in fact, have glaucoma-like visual field defects,” Dr. Semes said. “Sorting this out is sometimes very difficult and requires following the patient to see if a progression of field defects exists.”

Myopia

Myopia should also be considered a risk factor for glaucoma. “When evaluating the optic nerve, the configuration can be very confusing,” Dr. Semes said. “There may be myopic stretching because the eyeball is longer. Or is the configuration truly a glaucomatous defect?”

Likewise, family history has been shown “to be stronger in the same generation than among ancestors,” said Dr. Semes. “For instance, if I was to be diagnosed with glaucoma, my younger brother would be at greater risk than my children.”

Age, ethnicity

Steven L. Mansberger, MD, MPH, a glaucoma specialist and an assistant scientist at Devers Eye Institute (Legacy Health System) in Portland, Ore., has developed a glaucoma risk calculator. “Age and ethnicity are two of the most common risk factors,” Dr. Mansberger told Primary Care Optometry News in an interview. “Patients older than 40 are at a dramatically higher risk of developing glaucoma and developing progression. There is not a linear relationship with age, but probably a curvilinear relationship; in other words, a very slow increase in risk. But as patients get older, that risk increases even more.”

Blacks and Hispanics have a significantly higher risk of developing glaucoma during their lifetime. “The prevalence of glaucoma in Caucasians is 2%, compared to 8% in these two groups. So the risk is four times,” Dr. Mansberger said. “We don’t know the reason. It might be some sort of genetic predisposition to developing glaucoma. Lifestyle or diet may also play a role.”

Lack of access to health care may be a possibility, too. “Blacks and Hispanics have higher risks of developing lots of other medical disorders, including hypertension,” Dr. Mansberger said.

Diabetes

Diabetes is another risk factor. “Because many diabetics schedule annual eye exams, glaucoma is detected more often,” Dr. Mansberger said. “Clinicians should evaluate the optic nerve carefully.”

A higher incidence of glaucoma in diabetics may be attributed to a vascular process. “Vessels become sugar-coated, and blood flow to the optic nerve may be decreased,” Dr. Mansberger said.

Thin cornea

Central corneal thickness was highlighted in the OHTS. “It was so significant that it rose to the level of a possible risk factor for glaucoma,” said Eve J. Higginbotham, MD, who is one of the vice chairs of the study. “A thinner cornea represents higher risk. We think central corneal thickness is important because of the underestimation that occurs when one has a thin cornea.

“We need to keep in mind that the technique of Goldmann applanation was based on an average corneal thickness of 520 µm,” Dr. Higginbotham continued. “A number of individuals have thinner corneas than that. There is also literature to suggest that people who have ocular hypertension, as in the OHTS, tend to have thicker-than-normal corneal thickness measurements. Thicker corneas would certainly overestimate pressure. So, a number of the patients in the OHTS probably had a normal range of pressures.”

The status of the fellow eye offers a clue about the likelihood of developing glaucoma. “If the fellow eye already has some deterioration of either the optic nerve or the visual field, there is a greater risk that glaucoma will develop in the eye that is being followed,” Dr. Higginbotham said in an interview.

This risk is estimated to be 20 to 25 times greater than in a patient with both eyes normal, she said.

Women are at greater risk of developing progressive glaucoma at low pressures and may be more prone to angle closure. “In part, women tend to live longer,” said Dr. Higginbotham, professor and chair of the Department of Ophthalmology and Visual Sciences at the University of Maryland School of Medicine in Baltimore. “The Rotterdam Study also found that women who experienced early menopause (younger than 45 years of age) actually seemed to be at greater risk. This suggests that there might be some protective benefit of having exposure to estrogen for as long as possible.”

Risk calculator

Dr. Mansberger said that his glaucoma risk calculator “has been very well received by eye care providers. We now have more than 200 registered users. It simplifies complex findings of various studies that enable a clinician to apply study results to an individual patient.

“For example, the Ocular Hypertension Treatment Study (OHTS) lists six factors associated with glaucoma,” he continued. “This translates into some 1,600 different combinations of results. The calculator determines the average risk of a particular patient developing glaucoma over the next 5 years.”

Dr. Semes has used the risk calculator on about 20 patients. “I feel it is a valuable tool. It combines a lot of very solid clinical findings, including cup-to-disc ratio and functional or sensitivity testing via the pattern standard deviation from the visual field,” he said. “However, the threshold for treatment recommendation is slightly lower than I would have expected. It is around 8% to 10%.”

For Your Information:

• Leo P. Semes, OD, FAAO, can be reached at UAB Optometry, 1716 University Blvd., Birmingham, AL 35294-0010; (205) 934-6773; fax: (205) 934-6758; e-mail: LSemes@icare.opt.uab.edu.
• Steven L. Mansberger, MD, MPH, can be reached at Devers Eye Institute, 1040 Northwest 22nd Ave., Ste. 200, Portland, OR 97210; (503) 413-6453; fax: (503) 413-6937; e-mail: smansberger@discoveriesinsight.org.
• Eve J. Higginbotham, MD, can be reached at 419 W. Redwood, Ste. 580, Baltimore, MD 21201; (410) 328-5929; fax: (410) 328-6246; e-mail: fcwejh6786@aol.com.

• Dr. Mansberger’s glaucoma risk calculator can be accessed at www.discoveriesinsight.org.