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OHTS: IOP-lowering drops can delay glaucoma onset
The results of the 5-year Ocular Hypertension Treatment Study (OHTS) have shown that treating patients at risk for developing glaucoma with intraocular pressure-lowering drops can delay the onset of the disease.
“These are fascinating findings. They support the treatment of patients at highest risk,” said G. Richard Bennett, OD, FAAO, of the Pennsylvania College of Optometry (PCO). “However, this does not mean that every patient who is ocular-hypertensive will need treatment. In fact, most won’t.”
Dr. Bennett, who is an associate professor and director of glaucoma services at PCO, served as a principal investigator for the OHTS, which was conducted at 22 sites across the country.
Dr. Bennett was the only optometrist to act as a principal investigator in the study, and PCO was the only college of optometry involved. This distinction was earned through a competitive grant from the National Institutes of Health, Dr. Bennett said. OHTS researchers enrolled 1,636 people between the ages of 40 and 80 years old with elevated IOP but no signs of glaucoma. Half the group was assigned daily eye drops to control IOP, and the other half were observed.
The pressure-lowering drops reduced by more than 50% the development of primary open-angle glaucoma (POAG). Of the patients receiving medication, 4.4% developed glaucoma over the course of the 5-year study; by comparison, 9.5% of control patients developed glaucoma.
Participants on medication had their IOPs reduced by about 20% during the course of the study.
“Another thing we found out in the study is that we have been able to identify people at higher risk,” Dr. Bennett said. “We did an ancillary study measuring corneal thickness using a pachymeter, and we found that corneal thickness was a significant prognostic factor.”
There are several possible reasons for this factor, Dr. Bennett said.
“We know that the artifact induced by Dr. Goldmann’s algorithm assumes a normal-thickness cornea,” he said. “A fat cornea will artifactly measure high. So, you tend to err on the side of the angels – if the pressure’s high, you get scared and do something.”
In other words, Dr. Bennett explained, if a practitioner were to measure 20 mm Hg with a very thin cornea, there will not be a good algorithm.
“The algorithm doesn’t work as you reach the extremes of corneal thickness,” he said. “So, there is no number that we can give the practitioner; just that if you have a cornea that is thin, you know the pressure is high and the patient is at greater risk,” he said.
Implications of the findings
Dr. Bennett said he feels the results of the OHTS will have a positive effect on the diagnosis and treatment of glaucoma.
“In the past, there was no standard of care – practitioners did all kinds of things just based on their own prejudices,” he said. “There were clinicians who would treat everybody above a 22 mm Hg and those who wouldn’t treat anybody unless they showed damage on a visual field. And we know that once considerable damage has been done, it shows up on the visual field.”
Dr. Bennett cautioned that practitioners should be careful in assessing each individual case. “The idea is, we don’t want to treat everybody,” he said, “but we certainly want to carefully observe these folks. The patients at highest risk should probably be treated now.”
The new findings are likely to help practitioners in deciding how to proceed, Dr. Bennett said. “I believe this will make the prudent clinician more aggressive in treating patients at higher risk and will help him or her to feel comfortable watching patients at lower risk,” he said.
For Your Information:
- G. Richard Bennett, OD, FAAO, can be reached at 8360 Old York Road, Elkins Park, PA 19207-1598; (215) 780-1400; fax: (215) 780-1336.