Our goal over the past several decades has been to find the “holy grail of laser-ology”: the ability to achieve the best vision possible while minimizing tissue damage. There has been a quietus in development and experimentation with lasers, but I think that period is over, and we are coming into an interesting new era of lasers. I will briefly discuss the evolution of the yellow laser, some key features of the IQ 577 Laser System and a topic close to my heart, the micropulsing of lasers.

TRUE YELLOW LASER RE-EMERGES
In the late 1980s, 577 nm laser technology was introduced in the form of a large, tunable dye system, requiring special electrical and water conduits for power and cooling. One of the key advantages of the 577 nm wavelength is that it avoids absorption in xanthophyll, allowing treatment closer to the macula. Another notable difference is 577 nm lasers can produce a visible burn with less power and less collateral damage than produced by the blue-green or green laser wavelengths. This translates into less discomfort for patients, less axial and lateral thermal spread, less anatomical and functional damage, and less progressive scar enlargement. Our goal is to get the job done with the least amount of tissue damage and scarring, so in this case, less truly is better.

Ophthalmologists' interest in a yellow laser always has been high; however, the technology succeeding dye lasers gravitated toward solid-state systems and away from the key 577 nm wavelength. Although other “yellow” lasers eventually emerged, their wavelengths differed from 577 nm and did not offer the same advantages. As shown in Figure 1, not only does the preferred 577 nm laser have peak absorption in oxyhemoglobin, but it is more efficient than 532 nm and 561 nm systems. Furthermore, the “yellow” 561 nm lasers are even less efficient than the conventional green (532 nm) systems.

In 2008, Iridex brought back the true-yellow 577 nm wavelength, this time in a solid-state platform, the IQ 577. This is the first ophthalmic photocoagulator to incorporate a solid-state laser capable of delivering up to 2 watts of power at the critical 577 nm wavelength. The stability and reliability of a solid-state device coupled with the ability to deliver faster treatments and create smaller lesions with more controllable, reproducible, lighter burns make it a truly desirable system.

In 2008, Iridex brought back the true-yellow 577 nm wavelength, this time in a solid-state platform, the IQ 577. This is the first ophthalmic photocoagulator to incorporate a solid-state laser capable of delivering up to 2 watts of power at the critical 577 nm wavelength. The stability and reliability of a solid-state device coupled with the ability to deliver faster treatments and create smaller lesions with more controllable, reproducible, lighter burns make it a truly desirable system.

IQ 577 ADVANTAGES
The advantages of using a 577 nm laser are clear. Retinal photocoagulation with the IQ 577 is characterized by the highest oxyhemoglobin absorption, the highest oxyhemoglobin- to-melanin absorption ratio, negligible uptake by macular pigments including xanthophyll, lower phototoxicity, lower scatter, lower treatment power requirements, and excellent visualization of even the mildest tissue reactions.

I started using the IQ 577 about a year ago. Compared with the green laser, I can see that the IQ 577 creates a precise, well-defined burn with minimal bloom. That is an advantage when your goal is to make smaller, lighter lesions in the retina. Immediately, I noticed the ability to treat with significantly less power, in some cases 50% to 70% less. Likewise, I could reduce the pulse duration to further minimize the discomfort to the patient.

Patients are more comfortable with treatment by the IQ 577, and they will tell you so. Pain level depends on the wavelength (absorption), the duration of application (pulse length), and the power setting. Because the IQ 577 is a more efficient laser and its wavelength is well absorbed in the retina, you can reduce the power, reduce the duration of beam application, and consistently see a sharp, concise spot.

Higher efficiency means lower power settings, and reducing the duration and power help reduce pain and discomfort, especially with panretinal photocoagulation (PRP) and other laser-intensive treatments. For example, when performing a PRP with a 500 μm spot size, you can set the time at 0.07 seconds and reduce the power to less than 200 mW. You still produce a nice lesion that will not spread, and it is much more comfortable for patients. The need for retrobulbar anesthesia is eliminated.

Also interesting for me is the repeatability of the laser burn. Unlike other systems, when using the IQ 577, I have to readjust the power only a couple of times at most during a treatment. The laser is efficient, in that it can achieve a consistent lesion throughout the retina, regardless of the local pigmentation of the target area. In short, it performs with nearly “set it and forget it” treatment parameters.

Finally, the IQ 577 provides uncompromised visualization. When performing photocoagulation, achieving the desired endpoint depends on our ability to accurately visualize the coagulation effect on the retina. Older systems with dark safety filters made seeing the endpoint difficult. The IQ 577 laser with new, clearer safety filters does not compromise our view of the retina.

INTUITIVE SYSTEM
I am the kind of person who does not usually read the instruction booklets. My evaluation of a new product has a lot to do with how easily I can learn to use it without reading the manual. The IQ 577 is totally intuitive. Everything is where it should be. It is easy to use and user-friendly. The laser console and the remote have the same controls, and a wireless power-adjust foot pedal allows you to adjust the power to titrate the intensity of the burn. It is beautifully designed with ergonomic user-interface, color touch-screen graphics, voice prompts, and dual-port device connectivity.

Someone asked me recently what criteria I would use if I were buying a new laser today. Clearly, having the 577 nm wavelength is a tremendous advantage, but micropulsing also will be necessary in all the lasers of the future. If you buy a system without the ability to pulse the laser, you're basically buying 20- or 30-year-old technology.

MICROPULSE ADVANTAGE
Iridex has been a leader in the concept of micropulsing since its introduction in 1992. The laser delivery mode allows much finer control of the output and, thus, the lasertissue interaction. It gives you more control over the thermal effects of the laser on the tissue and facilitates tissuesparing procedures. It has been used successfully to treat patients with diabetic macular edema, proliferative diabetic retinopathy, central serous retinopathy, and glaucoma.

With the old continuous-wavelength laser, you dial in one- or two-tenths of a second and press the pedal, triggering an event that is out of your control. The retinal temperature rises until the end of the pulse, triggering thermal decay, which further heats and coagulates nearby tissues even after the pulse terminates. You have no control over this thermal decay process, making it easy to overtreat or perforate the choroid during macular treatment, especially when using a small spot size.

MicroPulse introduces a novel way to manage laser-tissue interaction (Figure 2). Instead of a single large laser pulse, you introduce a series of multiple, short (microsecond)pulses. Each short pulse creates a small thermal effect in the tissue. The temperature of the tissue decays back to baseline after each micropulse and prior to arrival of the next pulse. The heat deposited during each micropulse is small, so the subsequent thermal decay is largely confined to the immediate target region.

The pulse is set, the duty cycle is set, and now you can control the final laser-tissue interaction by gradually increasing the power. The thermal effect is not additive. This makes it virtually impossible to perforate the choroid or get a surprise white burn, which can happen with other lasers, including the green laser. This level of control and target specificity afforded by micropulse was not possible using older, continuous-wave lasers. You have exquisite control over the final laser-tissue interaction. A laser without this feature is already an obsolete laser.

SUMMARY
The IQ 577 has an elegant design and an excellent user interface. The console is immediately responsive. Performance is very good, and compared to the green laser, less power is required to create most burns. You can consistently achieve the desired goal of mild, light but effective burns. You can see the burns earlier, and they are more reproducible. Treatments take less time, and patients are more comfortable and happier.

Robert P. Murphy, MD, practices at the Chevy Chase (MD) and Fairfax (VA) offices of the Retina Group of Washington. Before entering private practice, he was on the ophthalmology faculty at Johns Hopkins, where he was the principal investigator of the ETDRS, the MPS and the AREDS.