MIAMI – Researchers here recommend observation when first treating patients with normal-tension glaucoma because the disease may be related more to the sensitivity of the optic nerve than to IOP alone.
“Having the disease with a low pressure simply means that the optic nerve is very sensitive to that pressure, and if you lowered the pressure, the disease [would be] slowed,” said Douglas Anderson, MD, a professor of ophthalmology at the Bascom Palmer Eye Institute here.
Once progressive visual field loss is noted in one eye, medication would be recommended. Surgery would be performed as a last resort, he said.
Dr. Anderson said he and Stephen Drance, MD, have been leading a study on normal-tension glaucoma (NTG) for the past 15 years. He provided an update on the latest findings at the Bascom Palmer Inter-American Course in Clinical Ophthalmology.
The study has shown that medical therapy lowered IOP as much as surgery, and that the disease did not progress in some patients. It has also identified several risk factors for the progression of NTG. If untreated, NTG patients with progression have the same degree of damage as those with open-angle glaucoma.
“Almost everyone considers these two conditions to be essentially the same disease,” Dr. Anderson said.
Clinical effects of treatment
The study currently includes 300 patients. The patients selected already had cupping of the disc and a visual field defect that threatened fixation, Dr. Anderson said. Patients whose visual field defects were stable were not included.
In the study, patients were initially split into two groups: in one group patients received treatment, and in the other group visual fields were observed every 3 months for the first year and every 6 months thereafter. The goal for the treated group was to reduce their IOP by 30% with medication and laser alone. Patients in the untreated group began medication once progression was defined in one eye.
Because untreated patients progressed by 80% and progression slowed in treated patients, researchers concluded that NTG was the same as open-angle glaucoma because the optic nerve was affected the same way. Almost half of the treated patients had their IOP reduced by 30%.
“This was a surprise to us. We had thought that most patients would require surgery in order to achieve a pressure of 12 or 13 mm Hg,” Dr. Anderson said.
Surgery was performed on half the treated patients who continued to progress, cataracts developed more quickly in them, and their visual outcomes were not as successful, he said.
The second stage of the study was to determine the risk factors for progression of the disease. Three factors were identified: gender, history of migraine or vasospasms and disk hemorrhage. There was a slight indication that race was a factor, but there were not enough patients to show statistical significance. Women were found to progress more rapidly. Age was not a factor for progression, Dr. Anderson said.
“Only half of the patients who present with normal-tension glaucoma will progress over a period of 5 to 7 years. This brings up the question as to whether treatment should always be started on everyone who presents with glaucoma,” he said.
Dr. Anderson suggested observing the patient who presents with a mild visual defect. If the defect advances and threatens fixation, he recommends aggressive treatment before considering surgery. He advises treating one eye and seeing if the glaucoma progresses in the other eye to observe how much it lowers IOP.
“This would be considered conservative treatment. Each physician should make up [his or her] mind about each case, but we should remember that half the cases will not progress without treatment,” he said.
“This is a new idea for all of medicine,” he said. “We are certainly used to the idea that certain drugs will lower IOP better than others, but in some patients, different drugs work better. Those are the people in whom we want to study the risk factors further so that treatments can be devised for their pathogenic factors.”
For Your Information:
- Douglas Anderson, MD, can be reached at the Bascom Palmer Eye Institute, P.O. Box 016880, Miami, FL 33101; (305) 326-6146; fax: (305) 326-6306.
- Anderson, DR. Normal Tension Glaucoma study. Clinical Trials in Ophthalmology: A Summary and Practice Guide. Baltimore, MD: Williams & Wilkins. 1997; pp. 335-348.