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ODs apply results of pivotal studies to their glaucoma practices
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Armed with the results of two seminal studies, the Ocular Hypertension Treatment Study (OHTS) and the Early Manifest Glaucoma Trial (EMGT), practitioners are now able to more effectively diagnose and treat patients with glaucoma. As the implications of these studies come to be fully understood, optometrists are beginning to incorporate this new knowledge into their practices.
“These studies dramatically increase the responsibility a primary care optometrist has in the diagnosis and management of glaucoma,” said Richard Noyes, OD, in private practice in Cedar Rapids, Iowa. “It becomes incumbent upon us to make the diagnosis earlier.”
The OHTS
Prior to the OHTS, no definitive data showed that reducing elevated intraocular pressure would delay or prevent the onset of glaucoma. Gaining this information was the primary goal of the OHTS, according to G. Richard Bennett, MS, OD, FAAO, a principal investigator for the study.
“The study was intended to evaluate patients who did not have glaucoma, but who were at increased risk of developing it due to their elevated intraocular pressure,” Dr. Bennett said. “Until this point, there was no consensus on the efficacy of medical treatment in this situation. Therefore, we designed a randomized clinical study called the OHTS.”
Patient recruitment for the OHTS took place between Feb. 28, 1994, and Oct. 31, 1996. A total of 1,636 individuals were chosen to participate: 817 were assigned to topical ocular medication, and 819 were assigned to observation. All of the medications used in the study were commercially available.
The study found that eye drops used to reduce pressure inside the eye were effective in delaying onset of primary open-angle glaucoma.
“The conclusion of the study, in a nutshell, involved the fact that topical ocular hypertension medications are effective in delaying the onset of open-angle glaucoma,” Dr. Bennett said.
Earlier treatment effective
Dr. Noyes said the study has provided practitioners with important guidelines for diagnosing and treating glaucoma.
“Specifically, we now know that target pressures in the range of 16 mm Hg contribute to significantly better outcomes over a 5-year period than the previous rule of just lowering the pressure by 20%,” he said. “Secondly, we know that early treatment makes a significant difference in the outcomes for patients, and we do need to treat earlier than we used to believe.”
In addition, Dr. Noyes cited study findings that make a correlation between a drop in pressure and decreased risk in blindness in a glaucoma patient. “When the pressure is about 19 mm Hg, for every one point in pressure drop, we get a 10% drop in the risk of blindness from glaucoma,” he said.
Corneal thickness as a factor
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Dr. Bennett said one unexpected finding from the study was that certain risk factors can help practitioners determine which patients should be treated. “One risk factor, when we looked at the univariate analysis, was black race,” Dr. Bennett said. “However, when we used multivariate analysis, we found that black race dropped out if you measured for central corneal thickness and also if you measured for large cup-to-disc ratio.”
Dr. Bennett said a group of black patients with elevated pressure were more likely to develop glaucoma if they were under observation during the 5-year time frame of the study.
“But if you eliminated the variables of central corneal thickness and large cup-to-disc ratio, you eliminated the factor of race,” he said. “And it could be the reason that African-American patients developed this disease so much more commonly than white people. It is because of thin corneas and big cups.”
Dr. Bennett recommended that optometrists begin to take central corneal thickness measurements on all ocular hypertensives and glaucoma patients. “And also, rather than watching, clinicians should assess relative risk, including central corneal thickness, and consider initiating treatment for individuals with ocular hypertension who are at moderate or high risk. This condition seems to be more dangerous than we thought before,” he said.
The EMGT
Another landmark glaucoma study, the EMGT followed 255 patients, ages 50 to 80 years, with early glaucoma in at least one eye. One group was treated immediately with IOP-lowering medicines and laser, while the control group was left untreated.
Both groups were followed carefully and were monitored every 3 months for early signs of progression. All control group patients whose glaucoma advanced were provided with treatment.
After 6 years of follow-up, investigators found that progression in the treated group (45%) was less frequent than in the control group (62%), and onset was significantly delayed in the treated group.
“The EMGT was a much smaller study,” Dr. Bennett said. “But, again, they found that, in patients with early glaucoma, treatment was helpful in delaying progression.”
Dr. Noyes agreed that the EMGT’s findings are consistent with those of the OHTS.
“It basically found that when you’re in the range of 19 or 20 mm Hg, supposedly for every point of pressure, that amounts to a 10% decrease in the risk for visual field loss,” he said. “Now, that is probably a little loose, because if you drop 10 points from 40 to 30, it doesn’t mean you’re out of the woods. But it is still an important study along the same lines as the OHTS.”
The AGIS
Another valuable study, according to Dr. Bennett, is the Advanced Glaucoma Intervention Study (AGIS). This study was designed to evaluate the long-range outcomes of medical and surgical management in advanced glaucoma.
In this study, patients with advanced glaucoma who had failed medically were randomized into surgical groups employing a preset algorithm of argon laser trabeculoplasty and trabeculectomy. Another aspect of the study examined the role of IOP reduction in preventing further damage.
“The AGIS study says that not only is there a protective effect of getting the patients under control, but that getting the patient consistently under excellent control is really important,” Dr. Bennett said. “So you can stratify the results of that study by looking at patients who were 100% controlled during the course of the study at low pressures. You go up the stratification, and you see that, gradually, people started to progress.”
The role of instrumentation
One way in which practitioners have incorporated these recent study results into their practices is by obtaining more information using new instrumentation, according to Dr. Noyes.
“Familiarity with and utilization of new technologies is one area in which we, as primary care optometrists, need to ‘up the ante’,” he said. “We need these technologies because they help us to intervene earlier. And we know that we now have a responsibility to intervene earlier and more aggressively than we did before.
“We use the GDx VCC (Laser Diagnostic Technologies, San Diego) regularly in our office to measure the nerve fiber layer in glaucoma suspects, ocular hypertensives and those with confirmed glaucoma,” he continued. “We use it to determine if the patient needs intervention or monitoring.”
In addition, the GDx VCC allows Dr. Noyes to measure the efficacy of the treatment he has initiated. “In other words, we want to be sure that if there is damage occurring, we interrupt that process,” he said. “We need to be using equipment that helps us make a correct diagnosis earlier, to make sure we are not overtreating those who do not need treatment and that we are adequately treating those who do need treatment.”
Kristen Brown, OD, FAAO, who practices in Roxbury, Mass., has found the pachymeter to be quite useful in diagnosing and treating glaucoma. “The pachymeter, probably more than anything, has changed the way we look at patients in terms of glaucoma,” Dr. Brown said.
She said pachymetry readings have influenced her to make more changes in her treatment plan than results she obtains from a nerve fiber analyzer or blood flow analyzer. “If a patient has high pressures but a thick cornea, I have a little less concern about him or her developing glaucoma, or it progressing,” she said. “However, if someone has thinner corneas and a high pressure, I am more concerned.”
Earlier treatment?
With the release of these pivotal study results comes the potential for earlier detection and treatment for glaucoma patients, practitioners claim. However, the decision to begin treatment depends upon the individual optometrist.
“I will tend to begin treatment earlier if, for example, the patient has high pressures and a thin cornea,” Dr. Brown said. “I don’t know that corneal thickness in and of itself is a risk factor for glaucoma — it needs to be considered in light of other factors.”
Dr. Noyes said he would consider a combination of factors in deciding whether to initiate glaucoma treatment.
“The real key in the past has been intraocular pressure and visual fields, and we now know that nerve head and nerve fiber layer changes precede visual fields by 3 to 7 years,” he said. “So if early intervention is truly a key, then we have to be moving toward equipment and techniques that allow us to be 3 to 7 years ahead of changes in visual field.”
Dr. Bennett emphasized that the take-home message of the OHTS is not to treat every ocular hypertension patient. “That factor alone should not determine who should be treated. You cannot treat these patients based on moderately elevated pressure,” he said. “You have to look at the whole package to figure out the individual risk for the patient.”
For Your Information:
- Richard Noyes, OD, practices in Cedar Rapids, Iowa. He can be reached at 510 Tenth St. SE, Cedar Rapids, IA 52403; (319) 365-2868; fax: (319) 365-7831.
- G. Richard Bennett, MS, OD, FAAO, can be reached at The Eye Institute, 1201 West Spencer St., Philadelphia, PA 19141; (215) 276-6145; fax: (215) 885-9424.
- Kristen Brown, OD, FAAO, practices in Roxbury, Mass. She can be reached at Dimock Community Health Center Eye Care Service, 55 Dimock St., Roxbury, MA 02119; (617) 442-8800; fax: (617) 427-4566.