New laser options exist for patients with glaucoma

Glaucoma specialists look to the laser for effective, repeatable IOP reduction.

ByRochelle Nataloni

With open-angle glaucoma representing a leading cause of blindness in people over the age of 40, laser manufacturers have provided new tools to address this progressive disease.

In addition to the conventional technique of argon laser trabeculoplasty, two newer laser approaches are being investigated for lowering IOP. Lumenis introduced the Selecta II laser, recently approved by the Food and Drug Administration for trabeculectomy, at the American Academy of Ophthalmology meeting in New Orleans, and European and U.S. researchers are exploring the use of an Xe-Cl excimer laser for glaucoma treatment.

Selective laser trabeculoplasty

The Selecta II performs selective laser trabeculoplasty (SLT), which lowers IOP by using short pulses of low-energy laser light to target specific melanin-containing cells in the trabecular meshwork, which in turn stimulates an increase in fluid outflow. This selective technique is less traumatic to the eye than argon laser trabeculoplasty (ALT), which often causes scarring to the trabecular meshwork, according to Andrew G. Iwach, MD, a clinical professor of ophthalmology at the University of California, San Francisco (UCSF).

“In the mid-1970s, lasers became available in ophthalmology, and James Wise, MD, was credited with developing ALT, which has basically been in use since then. He showed that by applying energy to the trabecular meshwork you could achieve lower IOP. However, we also know from animal studies that if the same laser is applied and you overtreat, you can actually induce glaucoma in non-glaucomatous animal eyes. So, for more than 20 years, we have been using this laser procedure to injure the trabecular meshwork with heat,” Dr. Iwach said.

Studies show that ALT and SLT’s pressure-lowering abilities are similar. The idea of achieving the same pressure-lowering results without excessive damage to the trabecular cells was the setting in which the SLT laser was born, Dr. Iwach said.

The term trabeculotherapy has been used to describe the SLT technique.

“Rather than coagulating and actually shrinking tissue, theoretically it disrupts the organelles within the trabecular meshwork cells, so there is not as much collateral damage. You are using much less energy and hopefully just tweaking the cells and trying to get them to work better, as opposed to killing the cells,” he said.

Mark Latina, MD, who pioneered SLT at Wellman Laboratories at Massachusetts General Hospital in Boston, described its clinical results at the AAO meeting. When used as a primary therapy, he reported, SLT showed significant pressure reduction, and this has now been sustained over 36 months.

Repeatability

Dr. Iwach and glaucoma specialist Joel S. Schuman, MD, chief of glaucoma service at the New England Eye Center, said that in addition to lowering IOP without collateral damage to the trabecular meshwork, another advantage of SLT is that it is potentially repeatable.

“The theory is that since SLT does so little damage, maybe it is possible to go back, if necessary, and repeat the treatment. There are some indications, in some patients who have already undergone ALT and SLT, that SLT can be repeated. The hope is that this technology will have a better success rate than ALT with repeat treatments,” Dr. Iwach said.

“Unlike ALT, where you destroy a well-defined portion of the trabecular meshwork, you don’t see that damage, even microscopically, with SLT,” Dr. Schuman said.

Dr. Schuman has treated more than 50 eyes using the Selecta II for SLT.

“Our outcomes are very similar to what we’ve seen with ALT, with an average IOP reduction of about 20%,” he said. “One interesting thing is that anecdotally, we have found there are late responders. Some people do not respond at a month or even 6 weeks, but then they have a response at 2 or 3 months, and that’s encouraging.”

Another interesting finding that Dr. Schuman has seen in his SLT patients reflects an observation by Jorge Alvarado, MD, also of UCSF. Dr. Schuman has seen lower IOP in the contralateral eye following SLT, which is often seen with ALT. Dr. Alvarado describes the contralateral response as the effect of macrophages on the trabecular meshwork.

“We are activating the macrophages in one eye, but they circulate systemically and affect the trabecular meshwork in the other eye as well,” Dr. Schuman explained.

Also noteworthy are electromicroscopy studies by Dr. Alvarado and colleagues at the University of Arizona at Tucson.

“Using electromicroscopy [in SLT patients], they have not been able to detect damage to the collagen substructure of the trabecular meshwork, and Dr. Alvarado claims he does not even see any loss of cellularity in the trabecular meshwork in his studies. That’s very encouraging. I’m sure there is some loss of cells, but the fact that the damage is so minimal that it can’t even be detected using microscopy is exciting,” Dr. Schuman said.

Excimer for glaucoma

At the annual meeting of German Ophthalmic Surgeons in Nuremberg last year, Philippe Sourdille, MD, of Nantes, France, reported on the use of excimer laser trabeculotomy (ELT). The procedure uses a beam of UV radiation from an Xe-Cl excimer laser to increase aqueous flow by creating openings in the trabeculum and inner wall of Schlemm’s canal. He reported that the technique had produced significant reductions in IOP and glaucoma drug usage with no serious complications in 47 eyes of 47 patients with open-angle glaucoma in three European centers. Patients had been followed for periods ranging from 6 to 21 months, with an average of 8.2 months, he reported.

The ELT procedure begins with a 1-mm corneal incision using a precalibrated 20-gauge knife, followed by introduction of viscoelastic into the anterior chamber to deepen the angle in the area where the excimer laser ablation is performed. An angulated fiber optic is then introduced and a series of four to eight laser shots is applied to the trabeculum from 150 µm to 250 µm.

The postop regimen following ELT was pilocarpine for 5 days, and NSAIDs and prednisolone for 9 months. There were no postop complications associated with the procedure, although bleeding from the opening of Schlemm’s canal was not uncommon, but usually resolved spontaneously. The incidence of bleeding was reportedly higher in previously operated eyes than in virgin eyes. The laser used in the European study is manufactured by Glautec AG.

Regarding ELT, Dr. Iwach said, “The trick is not making the holes; the trick is keeping them open. There are lots of different techniques right now that are looking at partial-thickness filtering surgery, such as viscocanalostomy. With excimer, the consideration essentially is using a different wavelength, another way of making a surgical dissection. The bottom line is, although initially these techniques may appear to be very promising, long-term follow-up is necessary to determine if they are going to be around for the long term. These technologies are exciting, they’re interesting, but they’re not necessarily ready for prime time.”

“A number of studies have looked at laser thermal ablation with erbium laser and have shown you can get an increase in outflow facility with trabecular ablation,” Dr. Schuman said. “It’s an idea that’s come before and because of technical issues wasn’t fully explored. If this [excimer] is a laser that will be available to investigators, and the technology is reliable and relatively inexpensive, I think it could potentially be useful.”

Lasers in glaucoma surgery

Lasers have become a valuable tool in treating glaucoma, according to Ivan Goldberg, MBBS, FRANZCO, FRACS.

“For angle closure and combined-mechanism glaucomas, the YAG laser is utilized to create a peripheral iridectomy. This eliminates pupil block and protects patients from an acute attack of angle closure, breaks an existing attack and protects the trabecular meshwork from the repeated damage of intermittent angle closure, which may be associated with subacute attacks,” Dr. Goldberg said.

“In patients with thick, dark-brown irides, creation of an iridectomy often requires special techniques, such as making a surface pit in the iris with the argon laser first, and then penetrating through with the YAG laser itself as a secondary step. The two steps can and should be performed immediately after one another. Peripheral argon laser iridoplasty can also help eyes with iris bombe by tightening the peripheral iris away from the meshwork. While such an effect may be temporary, it may last for some years,” he said.

By contrast, Dr. Goldberg said, in eyes with primary or some secondary open-angle glaucomas not responding adequately to medical hypotensive therapy, applying argon to the meshwork offers an approximate 70% chance of pressure reduction. He said there is a 50% chance that such a response will still be present after 5 years. Because the meshwork is heavily pigmented in secondary open-angle glaucomas like pseudoexfoliative or pigment dispersion glaucomas, the hypotensive response can be expected in up to 90% of eyes.

“Because such a treatment, if performed with some rudimentary precautions, carries almost no risk of adverse effects, this is a procedure I like to recommend to patients before they consider drainage surgery,” he said.

He recommended prelaser topical instillation of pilocarpine, apraclonidine and dexamethasone and postlaser use of dexamethasone four times daily for 4 days, in addition to continuing the patient’s usual antiglaucoma therapy.

For ALT, Dr. Goldberg pointed out the need for sufficient power to yield a visible reaction in the trabeculum, but without excessive heat generation (evidenced by formation of a large bubble or an “explosion”). The laser applications must be on the junction of the mid- and posterior thirds of the meshwork without damaging the peripheral iris, ciliary body face or corneal endothelium. “In this way, peripheral anterior synechiae can be avoided,” he said.

After a successful laser peripheral iridectomy in eyes with combined-mechanism glaucoma status, gentle peripheral iridoplasty may be needed to allow laser access to the meshwork itself, without damaging adjacent structures.

Dr. Goldberg said lasers could also be used to reduce aqueous inflow by damaging the ciliary epithelium. This can be accomplished either ab externo with a diode laser, or ab interno through the pars plana.

“Because the therapeutic range is so narrow, under- and overtreatments can occur — with the need for retreatments in the case of undercorrection, and the risk of phthisis bulbi in the overcorrections. I prefer to reserve these techniques for eyes in which other treatment modalities have failed, or for pain relief in blind eyes as an alternative to enucleation,” Dr. Goldberg said.

Following drainage surgery, laser suturolysis can be helpful in encouraging aqueous flow if the scleral trapdoor has been sewn down too tightly.

“To facilitate such a technique, long bites with the 10-0 nylon sutures through the sclera offer a longer possible pathway for laser access, though ideally I like to cut the suture at the point it disappears into the sclera, away from the trapdoor. Cut at this point, it is unlikely that a short, sharp nylon end will stick upwards, jeopardizing the integrity of the overlying conjunctiva,” he said.

“Laser trabeculoplasty techniques can be regarded as equivalent [in terms of] eye pressure to an additional medication — one that is effective. Almost certainly, patients will need to continue their medical regimen. Only in rare circumstances is the hypotensive response so good that medications can be reduced or halted altogether. For example, sometimes laser trabeculoplasty is recommended as a first-line therapy for patients who cannot or who choose not to instill eyedrops,” Dr. Goldberg said.

Economic considerations

Economic considerations are the biggest stumbling block regarding widespread applicability of the Selecta II for SLT, according to Louis B. Cantor, MD, a professor of ophthalmology at Indiana University.

“The scientific data and the studies demonstrate that SLT is a pretty safe procedure, with efficacy that appears comparable to ALT. It looks repeatable, although I don’t think we know yet what the real long-term implications are and how many times we can repeat it,” Dr. Cantor said.

“It makes sense as an alternative to typical laser trabeculoplasty and appears to offer some potential advantages over standard ALT. But it’s an expensive laser that can only be used for this procedure at this time. To justify the cost for this machine, you’re going to need some reasonable volume for it to make sense.”

A note from the editors: Staff Writer Michael J. Walsh contributed to this article.
For Your Information:

Andrew G. Iwach, MD, can be reached at 490 Post St., Suite 608, San Francisco, CA 94102 U.S.A.; +(1) 415-981-2020; fax: +(1)415-981-2019. Dr. Iwach has no direct financial interest in the products mentioned in this article, nor is he a paid consultant for any companies mentioned.

Joel S. Schuman, MD, chief of glaucoma service, professor of ophthalmology, New England Eye Center, can be reached at 750 Washington St., Boston, MA 02111 U.S.A.; +(1) 617-636-7950; fax: +(1) 617-636-4866; e-mail: jss@mediaone.net. Dr. Schuman has no direct financial interest in the products mentioned in this article, nor is he a paid consultant for any companies mentioned.

Ivan Goldberg, MBBS, FRANZCO, FRACS, can be reached at Floor 4, 187 Macquarie St., Sydney NSW 2000, Australia; +(61) 2-9231-1833; fax: +(61) 2-9232-3086; e-mail: igoldber@bigpond.net.au. Dr. Goldberg has no direct financial interest in the products mentioned in this article, nor is he a paid consultant for any companies mentioned.

Louis B. Cantor, MD, can be reached at the Indiana University Department of Ophthalmology, 702 Rotary Circle, Indianapolis, IN 46202-5175 U.S.A.; +(1) 317-274-8485; fax: +(1) 317-278-1007; e-mail: Lcantor@iupui.edu. Ocular Surgery News could not confirm whether Dr. Cantor has a direct financial interest in the products mentioned in this article or if he is a paid consultant for any companies mentioned.

Lumenis, manufacturer of the Selecta II laser, can be reached at 2400 Condensa St., Santa Clara, CA 95051 U.S.A.; +(1) 408-764-3000; fax: +(1) 408-764-3660.