System Brings Efficiency to Dual Wavelength Photocoagulation
Red and green wavelengths in dedicated
slit lamp address virtually all retina disease states.
NATALONI, CONTRIBUTING WRITER
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
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."
The Integre Duo integrates the
standard-of-care green wavelength at 532 nm and a visible red wavelength at
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
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
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.
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"
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."
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
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."
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