Kyle J. Alliman, MD
Contributing Author
The utilization of lasers in Ophthalmology remains an indispensable part of nearly every practice. In particular, laser photocoagulation used to treat retinal vascular and glaucomatous processes is vital. For these applications, the wavelength of the lasers used determines depth of penetration and absorption patterns. More recently, the technology has been developed enabling the delivery of a more effective and efficient true peak yellow 577nm laser.
577nm yellow lasers have been used in Ophthalmology for over two decades. Chromophores inside the eye have different absorption peaks with oxyhemoglobin absorbing at 577nm in the yellow spectrum. Martin Mainster, MD, PhD sites the theoretical advantages of using a 577nm band as low absorption by macular xanthophylls and retinal toxicity, less scatter en route to delivery, and less melanin absorption with minimized damage to adjacent pigmented tissues. Overall, less energy is used to achieve the same results with less patient pain and discomfort.
The technology behind the resurgence of 577nm has much to do with the ability to deliver a solid-state pure yellow laser. Solid-state lasers are diode-pumped meaning they are pumped with laser diodes rather than with discharge lamps, gases, or dyes. Solid-state lasers tend to be more efficient with less electricity consumption and heat dissipation than their lamp, gas, or dye counterparts. Compared to dye lasers, solid-state lasers require much less maintenance and they eliminate the potentially carcinogenic use of dyes.
Moreover, they are generally more compact with less laser noise. Greg Halstead of Iridex states the new 577nm laser is able to generate 2000mW of laser light potentially deliverable to the tissue (dye lasers put out 600mW at best). While this is far beyond the need for general ophthalmic application, it is necessary for the second vital part of the new Iridex delivery system – Micropulse. Micropulsing in photocoagulation uses successive micropulses to deliver laser power rather than a single pulse. These “pulse trains” are only minimally additive and conduction of heat to adjacent tissues with temperature rise is lessened.
Dr. Mainster states that with the utilization of a laser system employing both a highly efficient 577nm band and micropulse technology, modern laser photocoagulation has the potential to be equally effective and at the same time less destructive. Contemporary photocoagulation is suprathreshold resulting in scars that expand postoperatively. However, with the newer system, it’s possible to stay below the level of visible scarring and still deliver clinically significant laser energy that evokes a healing response.
The 577nm solid-state yellow laser system certainly seems promising. A system that is more efficient with equal efficacy and fewer side-effects is theoretically ideal. Currently, only one solid-state 577nm yellow laser system exists for clinical application. Iridex just recently was issued 510k clearance by the FDA for their IQ 577 Laser System. So when will this new technology be available for clinical use? Hopefully, this new technology will be available by this year's AAO meeting in Atlanta.
References:
1. Halstead G. Email correspondence/interview. Jan, 2008.
2. Kent C. “Laser Evolution: True Yellow Meets Sold State.” Review of Ophthalmology. 14:06, June 2007.
3. Mainster MA. “New laser technologies may decrease, localize photocoagulation effects.” Ocular Surgery News.
4. Mainster MA. “Wavelength selection in macular photocoagulation. Tissue optics, thermal effects, and laser systems.” Ophthalmology. 1986; 93:952-8.
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