As we all are aware, diabetic macular edema (DME) is the cause of mild to moderate vision loss in about 40% of patients who have diabetes, so it is a formidable problem for us to manage. In the 1980s, we based our treatment for DME on contact lens examination. In those days, thickness was thickness, and there was no real distinction in terms of different types. Today, we have the benefit of better imaging technology that shows more detail within the retina, so we can decide which eyes may be more appropriate for a particular treatment.
The ETDRS study1 showed a reduction in vision loss with standard grid laser therapy, and patients were grateful, but most patients today hold us to a higher standard. My patients ask, “When am I going to see better, doctor?” Answering that can be a challenge, because often they have systemic issues that are difficult to manage.
In general, the benefits of laser photocoagulation include reduced retinal thickening and some slight visual improvement, but we are still grappling with the problem of thermal injury. The impact of inducing scotoma is sizable, particularly as it affects a patient's ability to read. Most patients do not experience appreciable visual acuity improvement
In recent years, researchers have investigated pharmacologic remedies, but the data have shown laser photocoagulation is still better for our patients with macular edema.2,3 Laser is our gold standard, and in terms of overall management, I think it will continue as such for some time. The question remains: How do we optimize laser therapy to enhance visual and anatomic results and minimize patient discomfort?
POLISHING THE GOLD
STANDARD
When Iridex introduced the IQ
577 yellow laser, I saw that it had
some interesting clinical advantages.
Visibility at the slit lamp is
better with the yellow laser.
Because 577 nm is at the peak
absorption of oxyhemoglobin, the
IQ 577 produces consistently sharp
burns. Blanching occurs with lower
power settings and is confined to a smaller area due to the
reduced scatter of the laser. In terms of panretinal photocoagulation,
the 577 nm yellow causes less pain because it uses
less energy than either 532 nm or 561 nm systems.
A notable feature of the IQ 577 is its ability to turn off the red aiming beam while the footswitch is depressed. This is important because the surgeon's eyes tend to fatigue, looking at the bright laser, even when the aiming beam is turned down as much as possible. With the aiming beam turned off, you can easily distinguish early burn development.
APPLYING THE “RESIDENTS TEST”
What I particularly like about the IQ 577 and find useful
for residents is that the eye safety filter system allows the
simultaneous use of a red-free filter on the slit lamp while
treating. As we know, the red-free accentuates the visibility
of xanthophyll pigment so the surgeon can clearly see the
fovea and the parafoveal region. We can see what we should
be treating from the fluorescein, but we cannot necessarily
distinguish it clinically, especially when viewing a fundus
image. Trying to decide where or how close to the macula
to treat can be difficult.
The red-free filter distinguishes the macular pigment and highlights any microaneurysms. The surgeon commonly will not treat with red-free light when using a green laser because it is somewhat disorienting, and visualization is compromised. With a green (532 nm) system, the protective filter blocks the green light coming from the slit lamp. It can be difficult to have the light bright enough to see without creating additional discomfort for the patient. With the IQ 577, however, we can comfortably see the target area because the filter blocks the yellow (577 nm) light—not the green light
I like to test certain theories with my residents because they do not have intellectual baggage from years in practice. I tell them, “I'm going to let you treat these areas, but you have to use the 577 nm yellow laser and see what it does.” Two residents so far have told me, “Using the red-free filter makes me a lot more confident. I know when I'm close to the fovea. With normal lighting, especially with macular edema, I don't have many landmarks.” That, in itself, is a big plus for the IQ 577 in terms of the surgeon's confidence compared to using the 532 nm laser (Figures 1 and 2).
To give a quick example of the ability to treat close to the fovea, Figure 3 shows the case of a 58-year-old man who was actively working but had reached a point where he was unable to drive. His BCVA was 20/80. Triamcinalone treatments did not produce improvement. After a single treatment with the IQ 577, his BCVA is 20/40–1, the central area resolved, and his fovea is visible again.
SUMMARY
The IQ 577 gives us more options than we have had in
the past. The laser provides improved visualization aided by
the ability to treat while using the red-free filter in the slit
lamp, and the 577 nm wavelength requires less power and
shorter pulse durations to treat, improving the patient's
comfort.
Richard B. Rosen, MD, FACS, FASRS, CRA, is a vitreoretinal specialist at the New York Eye and Ear Infirmary. He is Vice Chairman and Surgeon Director for the Department of Ophthalmology and Director of Ophthalmic Research at the Infirmary's Advanced Retinal Imaging Center. Dr. Rosen is a member of the scientific advisory boards of Clarity Medical Systems, OPKO, Optical Imaging, OD-OS, and Medical Devices, Inc.
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