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Laser technologies have altered glaucoma treatment dynamic
OSN continues its anniversary coverage with a look at how cyclodestructive and trabeculoplasty procedures have emerged as viable alternatives to drugs in the treatment of glaucoma.
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Surgical procedures that facilitate aqueous inflow and outflow have been touted by some since the 1970s as viable alternatives to drug treatment in glaucoma because they reduce IOP with no compliance issues and often with limited complications.
The technology began with a transscleral approach to aqueous inflow procedures, according to glaucoma specialists. Over the years, those procedures have been refined, and argon laser trabeculoplasty (ALT) and selective laser trabeculoplasty (SLT) have been introduced, developed and adopted for glaucoma treatment. The procedures are used as primary or secondary treatment, when medication has failed to adequately lower IOP.
Many physicians helped innovate the procedures, working to improve the techniques and researching applications. Hugh Beckman, MD, was instrumental in assisting in the development of both inflow procedure cyclophotocoagulation and outflow procedure ALT. In a telephone interview with Ocular Surgery News, the now-retired physician said that cyclophotocoagulation with a ruby laser pulse, performed transsclerally, was started in the 1970s. Before that, ablation of the ciliary body was performed with other forms of cryotherapy, he said.
Aqueous inflow procedures include cyclodestructive techniques such as cryotherapy, cyclophotocoagulation, contact and noncontact laser procedures, contact diode and endolaser. ALT and SLT are both aqueous outflow procedures.
“The first laser procedure in the eye was ruby laser iridectomy, followed by reports on ruby laser cyclophotocoagulation, followed by Nd:YAG and during that period, argon laser iridectomy began, followed by Nd:YAG iridectomy. Cyclophotocoagulation went on to be done by the diode laser, and SLT was developed,” Dr. Beckman said.
Cyclodestructive procedures
Cyclodestructive therapies work by destroying the ciliary body, to reduce fluid inflow to the eye, through laser or non-laser methods. According to a study by M. Bruce Shields, MD, in a 1985 issue of Transactions of the American Ophthalmological Society, cyclodestructive therapies that have been used in the past include diathermy, electrolysis and beta irradiation.
Variations on techniques abounded, as researchers examined different ways of combining and advancing technologies. A study by Martin Uram, MD, in a 1992 issue of Ophthalmology evaluated microendoscope photocoagulation, finding that the therapeutic modality, which combined endoscopic visualization of the ciliary processes with diode laser photocoagulation, was effective in managing intractable neovascular glaucoma.
In that study, 10 patients had a preop IOP ranging from 36 mm Hg to 62 mm Hg. Postoperatively, nine eyes had an IOP of less than 21 mm Hg, with three requiring medication, and one eye had a final IOP of 27 mm Hg.
Cyclocryotherapy and cyclophotocoagulation have also been widely used. In laser cyclophotocoagulation, a laser beam is used to destroy the ciliary body. Dr. Beckman said he felt that transscleral cyclophotocoagulation with the laser was a step forward from other forms of cryotherapy.
“Over a period of years, cyclocryotherapy just went by the wayside, and the laser procedures became more and more utilized,” Dr. Beckman said.
Complications from cryotherapy procedures often seemed to stem from the fact that many of the cases treated with the therapy were high risk and thus were difficult to treat, Dr. Beckman said
“In general, I always felt that a lot of problems from cycloablation came from the fact that doctors looked at it as sort of a one-shot procedure and then realized that the postoperative care had to be taken care of fastidiously,” Dr. Beckman said. “For instance, you had to titrate the amount of steroid that the patient was getting because if you prescribed too much steroid, you turned off the procedure and if you didn’t use enough, you tended to get lower pressures.”
Argon laser trabeculoplasty
ALT was first published as a new technology in a paper in 1979 by James Wise, MD, and colleagues. Dr. Beckman was also part of the first clinical research trial, which compared the efficacy of ALT as a primary treatment vs. timolol. The study concluded that ALT performed better than timolol. Dr. Beckman said the procedure was not immediately embraced by the glaucoma community, but it has increased in popularity over time.
“The fact that ALT, to some extent, wore off, seemed to put doctors off, but the truth is, it didn’t wear off as much as the timolol wore off. Patients who were treated with the lasers over a period of 10 years did better than those started with the drug,” he said. “We found ALT to be virtually harmless. There are few complications.”
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Later studies helped establish its efficacy. The Glaucoma Laser Treatment Trial looked at patients randomly assigned to one eye receiving ALT and the other receiving topical beta blockers. Of 271 patients, 44% of the ALT-treated eyes had IOP less than 21 mm Hg, the defined success at 2 years, and 20% of these eyes had IOP less than 21 mm Hg at 7 years on ALT alone, compared with 30% and 15%, respectively, of eyes initially receiving medication. Fields and discs did better in the laser first eyes, and the number of medications required for control was less.
According to Douglas J. Rhee, MD, an OSN Glaucoma Section Member, ALT utilizes the argon blue-green wavelength, and its thermal laser creates a burn in the trabecular meshwork. While ALT’s mechanism of action is still being researched, Dr. Rhee said that it most likely induces biochemical and physiologic changes that cause several actions to degrade the extracellular matrix.
He said both ALT and SLT provide treatment options for patients who have medication compliance issues, who have IOP that is not reduced with medications or who have other factors that render medical treatment unfeasible.
“The impact of ALT and SLT is that they dramatically expanded our armamentarium, and their excellent safety profile makes them highly desirable,” Dr. Rhee said.
Selective laser trabeculoplasty
SLT was developed by Mark A. Latina, MD, in the early 1990s and introduced to the market by Lumenis in 1998. In a telephone interview with OSN, Dr. Latina said he and his colleagues were looking to develop a laser that did not cause coagulation damage to the trabecular meshwork, as ALT did. He proposed that the coagulation effect was unnecessary and that it caused more damage to the meshwork than necessary. He said he was seeking a way to induce a biological change in the meshwork without creating thermal damage.
“The idea was to develop a procedure that would selectively target the cells, but not cause any thermal damage,” Dr. Latina said to OSN. “That was the research question – how to do that. We looked at a variety of different laser systems and pulse durations and figured out, in cell culture, how to selectively target the trabecular meshwork cells without affecting even adjacent cells. … We did that, and we figured out that the laser, which is currently being used, was a very effective means of selectively targeting these cells in a cell culture dish.”
SLT works by utilizing a 3-nanosecond, Q-switched, double-frequency Nd:YAG laser pulse to target melanin granules within pigmented cells of the trabecular meshwork, according to Dr. Rhee. He said SLT does not cause thermal coagulative damage to the meshwork endothelial cells because of that, but could cause structural changes at commonly used energy levels.
Dr. Latina and colleagues first used the technology in a study of monkeys in the early 1990s and found that the laser could target the trabecular meshwork cells without causing collateral or thermal damage. Next, they applied the technology to humans in a clinical trial in the mid-1990s. The study, published in the November 1998 issue of Ophthalmology, looked at 30 eyes of 30 patients with uncontrolled open-angle glaucoma and 23 eyes of 23 patients with uncontrolled open-angle glaucoma treated previously with ALT.
The researchers found that 70% of patients in both groups had an IOP reduction of at least 3 mm Hg. At 26 weeks of follow-up, they found that the mean IOP was reduced by 5.8 mm Hg in the group not treated with ALT and by 6 mm Hg in the group treated previously with ALT. Transient IOP elevation of 5 mm Hg or greater was seen in 24% of patients.
Dr. Latina said subsequent studies by other researchers have looked at the procedure as a primary therapy, finding that there is a 90% success rate when used as first-line treatment. He said the procedure has been modified since it was first introduced; it initially treated only 180° of the eye and now treats 360º, which has been found to be more effective at lowering IOP and has a longer effect. But overall, the laser technology appears to be “optimized” at this point, he said. In the future, research will probably focus on discovering the laser’s mechanism of action and improving its response rate.
“SLT has become a popular treatment now for glaucoma,” Dr. Latina said. “Many of the comprehensive ophthalmologists are finding it very effective in their practices. The patients enjoy it, too, because it’s simple to do, and it’s an in-office procedure.”
For more information:
- Hugh Beckman, MD, can be reached at 248-855-3300; e-mail: cbhb@concentric.net.
- Mark A. Latina, MD, can be reached at Reading Health Center, 20 Pond Meadow Drive, Suite 204, Reading, MA 01867; 781-942-9876; fax: 781-942-9877; e-mail: mark.latina2@verizon.net.
- Douglas J. Rhee, MD, can be reached at 243 Charles St., Boston, MA 02144; 617-573-3670; fax: 617-573-3707; e-mail: dougrhee@aol.com.
References:
- Latina M, Sibayan S, et al. Q-Switched 532-nm Nd: YAG laser trabeculoplasty (selective laser trabeculoplasty): A multicenter, pilot, clinical study. Ophthalmology. 1998;105:2082-2088.
- Shields MB. Cyclodestructive surgery for glaucoma: Past, present, and future. Trans Am Ophthalmol Soc. 1985;83:285-303.
- The Glaucoma Laser Trial Research Group. Results of argon laser trabeculoplasty versus topical medicines. The Glaucoma Laser Trial. Ophthalmology. 1990;97:1403-1413.
- Uram M. Ophthalmic laser microendoscope ciliary process ablation in the management of neovascular glaucoma. Ophthalmology. 1992;19:1823-1828.
- Wise J, Witter S. Argon laser therapy for open-angle glaucoma. Arch Ophthalmol. 1979;97:319-322.
- Erin L. Boyle is an OSN Staff Writer who covers all aspects of ophthalmology.