Article Date: 1/1/2007

Feature TEMPLATE

Solid-state System Brings Efficiency to Dual Wavelength Photocoagulation

Red and green wavelengths in dedicated slit lamp address virtually all retina disease states.

The advantages of having a red wavelength, with its inherent ability to easily pass through media opacities, as well as the standard green wavelength in one photocoagulation system are well known to retinal specialists. Equally well recognized are the disadvantages of housing inefficient, space-hogging argon-krypton photocoagulators, which require a complex cooling system as well as a dedicated electrical supply and considerable maintenance. The Integre Duo (Ellex, Adelaide, Australia) is a device that provides the clinical benefits of an argon-krypton laser with the convenience and efficiency of solid-state technology. This union of efficacy and efficiency was approved for distribution by the FDA earlier this year and is currently being placed in retina practices throughout the United States.

The Integre Duo is the first solid-state photocoagulator to deliver red and green wavelengths. For common procedures such as retinal photo-coagulation, laser trabeculoplasty, and iridotomy, the Integre Duo's green wavelength provides the standard of care. The red wavelength produces less scatter for better transmission through a cloudy cornea or lens, provides deeper penetration for effective treatment of choroidal vessels, and enables treatment in the presence of a hemorrhage (Figure 1).


While green is generally accepted as the "workhorse" wavelength for the retina, it is often helpful to have red when faced with more challenging cases, such as vitreous hemorrhage, says ophthalmic laser industry veteran and Ellex CEO Peter Falzon. "A standard green photocoagulator can't finish the job. You need a wavelength that will penetrate through the vitreous hemorrhage and coagulate the vessel below — and red allows you to do that," Falzon says. Other advantages to the red wavelength, Falzon explains, are "when you have an early cataract forming or if you want to treat a little bit deeper into the retina or the choroids."

 

COMPACT, USER-FRIENDLY DESIGN

The Integre Duo integrates the standard-of-care green wavelength at 532 nm and a visible red wavelength at
670 nm into a slit lamp complex. Its single-pump, dual wavelength cavity is located under the slit lamp, inside a height-adjustable table. The laser cavity houses 2 crystals and a switching mechanism that enables the diode to pump either the first crystal or the second crystal, which are doped with different rare earth elements — one that lases green and the other that lases red, Falzon explains.

The changeover from green to red and back is immediate, according to retinal specialist Francesco Bandello, MD, and for even greater convenience, all the treatment parameters can be set with either hand directly on the slit lamp. Dr. Bandello, professor of ophthalmology and chair of the Department of Ophthalmology at the University of Udine in Italy, was the lead investigator in the solid state system's clinical trials. He reports that the system, which he has employed for both clinical practice and research purposes, is "well designed, compact, and user friendly."

Dr. Bandello stresses that having the green and the red wavelengths in an innovative device such as the Integre Duo is a great advantage. "Almost all patients with retinal diseases can, in fact, be effectively treated by these 2 colors. The red wavelength is not absorbed by red pigments, and therefore it is able to reach the tissue target in cases of vitreous hemorrhage or other media opacities," Dr. Bandello says. "Furthermore, the red wavelength is less absorbed by macular pigment and therefore can be used for treatments involving the macular area." Dr. Bandello reports switching to the red wavelength in as many as 40% of his retina cases.

Software-controlled active light feedback, combined with what Ellex refers to as "TrueSpot optics," facilitates precisely delineated and homogeneous photocoagulation spots regardless of the energy setting. Exposure time ranges from 0.01 to 4 seconds, and spot size ranges from
50 μm to 1000 μm. TrueSpot optics refers to a uniform, sharp-edged top-hat beam. This, says Falzon, provides the benefits of a parfocal system, with the added comfort of low-power density at the cornea (Figure 2).

CLINICAL AND PRACTICAL ADVANTAGES

Associate Professor of Ophthalmology Paolo Lanzetta, MD, also of Udine University, is an Integre Duo user and investigator along with Dr. Bandello. His experience with the device has shown both that it offers clinical and practical advantages. "The 670-nm solid-state laser combines the good absorption spectrum of a red laser with the advantages of portable and less costly equipment," Dr. Bandello says. "Retinal whitening is obtained easily, and there is virtually no learning curve with the Integre Duo."

Dr. Lanzetta reports that the 670-nm wavelength is as clinically effective as the krypton red laser. "We have recently verified the structural and ultrastructural effects of a 670-nm red laser on pigmented rabbit retina. The effects observed are consistent with those reported for the krypton red laser," he says. "The red wavelength has excellent properties for laser photocoagulation of the retina. The absorption characteristics of the 670-nm diode wavelength are very similar to those of the 647-nm krypton laser. With regard to the transmission through the ocular media, the red wavelength has an excellent curve that is scarcely influenced by opacities and is very similar to the transmission of the 810-nm diode near infrared laser," Dr. Lanzetta says. Irradiation passes through the crystalline lens and vitreous opacities as well as hemorrhages, Dr. Lanzetta notes, adding that it is well absorbed by the retinal pigment epithelium and choroidal melanocytes.

Dr. Lanzetta describes using the Integre Duo in the treatment of various retinal conditions, including proliferative diabetic retinopathy (PDR), diabetic macular edema (DME), choroidal neovascularization in age-related macular degeneration (AMD), peripheral retinal tears, and many others. "In general," he says, "the technique and parameters applied during treatments were similar to those used with a red krypton laser. Irradiation has been possible and effective in all the cases treated."

One of the particularly noteworthy characteristics of this photocoagulator, according to users, is the high quality of the laser burn over the retina. "This is true with the use of any spot size, including the smallest one of 50 μm," says Dr. Lanzetta. "The whitening of the laser spot over the retina is uniform with an even distribution of the energy, and the unique optical system guarantees a low power density at the cornea, which is extremely important when a wide-field contact lens such as the quadraspheric lens is used" (Figure 3). In this case, he says, the plane of highest power density is moved from the fundus toward the cornea when the spot size is set to larger than 50 μm. "Due to the optical properties of the lens, the beam diameter is reduced by a factor of 2, which increases the power density at the cornea by a factor of 4," Dr. Lanzetta explains. "The optics of the slit lamp are very effective in providing a perfect shape and focus of the laser spot even in the very periphery of the retina" (Figure 4).

One of the great advantages of this photocoagulator, according to Dr. Lanzetta, is its integrated design. "This allows for very compact dimensions of the laser slit lamp complex and creates more working space for the physician, as well as easy and simultaneous access to the patient and laser controls," he says. "The compact design allows its installation in any office without the need of extra space," he adds, "and it is small enough to easily be moved from one treatment room to another within a private practice, ambulatory surgery center, or hospital setting."

COMBINATION THERAPY

Even with the increasing use of injectable therapeutics, photocoagulation remains a mainstay in the treatment of retinal disease, and with good reason, according to Dr. Bandello. "All the new treatments we have now are short-term therapies, but retinal diseases and AMD are chronic diseases," he says. "We cannot imagine that these new treatments will be a definite answer for the needs of our patients. We need other options, such as laser, to stabilize our results."

Dr. Bandello points out that the combination of therapeutics and laser treatment will improve the efficacy of therapeutic options. "This is basically the rationale for using photocoagulation together with intravitreal steroids," he says. "First, injection is able to improve the clinical situation: retinal thickness is reduced and new vessels also reduce. When all these positive events occur, performing laser treatment is able to produce better results, with less energy and fewer complications." Improved compliance is another benefit of combination therapy, he says, because "the patient does not have a worsening of visual acuity following laser treatment. Therefore, the patient is happy and collaboration is better."

Referencing the continued reliance on laser photocoagulation, Dr. Lanzetta also points toward the temporary nature of pharmacologic retinal treatment. "Pharmacologic therapy represents a major breakthrough in the cure of a number of retinal diseases, such as AMD, DME, and PDR. However, in most cases, patients need repeated treatments to control the disease," says Dr. Lanzetta. "This is true both for the use of antiangiogenic compounds and for steroids.

Dr. Lanzetta points out that there is a rationale for the use of combined therapies that target different steps and pathways of the diseases. For instance, he explains, in DME, steroids have been used extensively to stimulate fluid resorption. "Different routes of administration, dosages, and compounding have been studied. However, it is commonly accepted that the effect is temporary and most patients experience recurrent edema after the effect of steroids is finished. Laser photocoagulation following steroid administration with subsequent reduced thickness of the macula can contribute to stabilizing the disease with improved outcomes," he says.

Drs. Bandello and Lanzetta recently studied 3 different modalities of treatment for patients with naïve diffuse DME: laser photocoagulation according to the ETDRS guidelines, intravitreous triamcinolone injection, and intravitreal triamcinolone injection followed by laser photocoagulation. In the course of the follow-up, the third group had the best results in terms of visual acuity improvement and edema resolution as compared to the other two groups, which experienced only a temporary stabilization of the condition. This outcome suggests that the red laser with its favorable properties of transmission through media opacities and thin layers of blood may represent the ideal wavelength for combination therapy, according to Dr. Lanzetta. "Modern medicine is rapidly moving toward less invasive forms of therapies, and there is plenty of evidence that less invasive modalities of laser treatment can lead to beneficial results," he says. "Recent hypotheses postulate that full-thickness retinal damage may not be needed to obtain the therapeutic effectiveness, and experiments have shown that the positive effect of retinal photocoagulation is mediated by factors derived from the retinal pigment epithelium. A selective low-threshold targeting of retinal pigment epithelium cells might become the desired endpoint of a therapeutically effective laser photocoagulation in those retinal and choroidal diseases in which the retinal pigment epithelium plays an important pathogenetic and therapeutic role," says Dr. Lanzetta.

This all suggests that the future of laser application is dependent on treatments that can avoid or minimize unnecessary retinal damage and side effects and maintain the therapeutic efficacy — which brings the advantages of combination treatment full circle.

Falzon points out that the newer treatment modalities have created more interest and more patient flow for retina specialists, and he maintains that the laser represents a very important tool for helping to manage this new patient pool. "There's no 'silver bullet,' or single perfect treatment, for all disease states," says Falzon. "What we're hearing from ophthalmologists is that these newer pharmacotherapies enable them to maintain patients' vision longer and give them hope of maintaining sight longer and that laser photocoagulation plays an equal role in helping them do that."



Retinal Physician, Issue: January 2007