Results from two years of patient followup in a randomized clinical trial suggest that argon laser therapy may be a safe and effective alternative to eyedrops as a first treatment for patients with newly diagnosed open-angle glaucoma. However, because open-angle glaucoma isa chronic disease, study patients will continue to be followed up to three additional years to further assess the value of both treatments.
The Glaucoma Laser Trial (GLT), sponsored by the National Eye Institute of the National Institutes of Health, is being conducted at 11 centers including eight clinics.
After two years of treatment, the mean intraocular pressure of eyes in the “laser first” treatment group measured about two points lower than that of eyes treated with eye drops only. These eyes generally required less medication to control pressure than the eyes treated with eye drops only. Visual acuity and visual field changes were the same for both groups of eyes.
“This is a significant public health study,” said HHS Secretary Louis W. Sullivan, M.D., “because glaucoma is a major cause of blindness in middle-aged and older people. Moreover, open-angle glaucoma is the most common form of glaucoma in the United States, and a leading cause of blindness among African Americans.”
In open-angle glaucoma, minute changes within the eye gradually interfere with the flow of fluids that nourish the tissues in the front of the eye. If these fluids fail to drain properly, the resulting increased pressure inside the eye can eventually damage the optic nerve.
“Unfortunately, people usually are unaware that they have glaucoma until the damage has progressed enough to cause vision loss,”said James O. Mason, M.D., assistant secretary for health.
Many eye specialists begin glaucoma treatment with eye drops, either to improve fluid drainage or to slow fluid formation. If drops alone do not bring the pressure to an acceptable level, the doctor may also prescribe pills. If these medicines fail, the next step is either surgery to create a tiny hole in the coat of the eye or to improve fluid outflow by treating the drainage tissue with a laser. In an attempt to avoid use of medicines, some doctors recently have started open-angle glaucoma treatment with the argon laser.
Medical and laser treatments each have advantages and disadvantages. More is known about medicines, but they must be used daily and can produce annoying and sometimes serious side effects. Laser treatment is easy to administer, is relatively painless, and may reduce or eliminate the need for medicines. However, laser treatment does not always reduce elevated pressure and, in rare instances, may even increase it.
The purpose of the GLT is to evaluate the relative efficacy of the two treatments. To ensure that each patient received whichever proved to be the better treatment in one eye, all 271 patients received both types of treatment, one type in each eye, as determined by chance or lottery (randomization). If the initial treatment (either laser eye drops) failed to reduce adequately and sustain control of pressure,additional treatment with eye drops was prescribed, according to a set sequence. The treatment steps in the sequence progressed from low to high doses of single medicines and then to combinations of medicines at various dose levels.
After two years of followup, laser treatment alone was sufficient to control pressure in 44 percent of the eyes, compared to 30 percent of the eyes treated with the anti-glaucoma drug timolol alone. The percentage of laser-treated eyes that could be controlled with laser alone or laser with timolol was 70 percent. Although these early results for laser treatment look promising, after two years off followup more than half of the laser-treated eyes needed one or more medications to control intraocular pressure.
Dr. Carl Kupfer, director of the National Eye Institute, cautions that, “Glaucoma is a chronic disease with a variable rate of progression, and eye specialists need to await longer-term results of the GLT Follow-up Study in their overall evaluation of these forms of treatment for their glaucoma patients.”
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Citation: The Glaucoma Laser Trial (GLT): 2. Results of Argon Laser Trabeculoplasty Versus Topical Medicines. The Glaucoma Laser Trial Research Group. Ophthalmology. 1990 Nov. PubMed