Retinal vessels: Photocoagulation now safer

November 1, 2009

A new 577-nm solid-state laser allows retinal specialists to harness the benefits of yellow light for laser photocoagulation while providing a number of additional advantages.

New York-A new 577-nm solid-state laser (IQ 577, Iridex Corp.) allows retinal specialists to harness the benefits of yellow light for laser photocoagulation while providing a number of additional advantages, according to Richard B. Rosen, MD.

"There are several differences between yellow- and green-light lasers that translate into safer, better tolerated, and more effective photocoagulation of retinal vessels with use of a yellow-light device," said Dr. Rosen, vice chairman and surgeon director, director of ophthalmic research, New York Eye and Ear Infirmary (NYEEI), and professor of ophthalmology, New York Medical College, New York. "Due to the very high, selective absorption of the 577-nm wavelength by hemoglobin, treatment can be delivered using a relatively low energy level that makes it safer and more comfortable. In addition, fundus visualization is optimized with a yellow-light laser since it enables use of red-free filter.

"Adding to those intrinsic benefits of yellow light, the [new laser] features micropulse technology, which enables greater treatment precision with sub-visible threshold treatment capability, and it packages the technology into a user-friendly solid-state platform that is portable and easy to maintain," he said.

"Although recent studies indicate some promising results with intravitreal pharmacotherapy for branch retinal vein occlusion, laser photocoagulation still works the best, provides the most durable treatment effect, and remains the gold standard," Dr. Rosen said.

The ability to use a red-free filter with the yellow-light laser optimizes fundus visualization, which is an important benefit when treating macular pathology. For example, in diabetic macular edema where the normal anatomic landmarks are often distorted by increased retinal thickness, precise localization of the center of the macula can be difficult. This in turn presents challenges to delivering safe and effective treatment.

"In targeting pathology in the center of the macula in order to improve vision, surgeons walk a fine line between delivering the laser pulses too close to the center and thereby creating scotomas and not being close enough so that the disease is not effectively treated," Dr. Rosen said. "The ability to use a green filter with the yellow-light laser technology improves visualization to enable optimum treatment placement that will resolve the macular edema without causing adverse consequences."

Tissue sparing through micropulsing

The fact that the 577-nm wavelength matches the peak absorption for hemoglobin and does not have competing chromophores results in a safety advantage when treating retinal vascular pathology. Safety with the new 577-nm laser system is further enhanced because it is equipped with micropulsing technology. The visible-light laser incorporates this delivery mode that divides each laser pulse into microsecond bursts, which helps to concentrate the laser energy within the target site and minimizes the risk of unwanted collateral tissue damage. Surgeons can adjust the on-time (pulse width) and off-time (interval between pulses) to minimize damage to the overlying retina to sub-threshold levels while still providing adequate stimulus to the retinal pigment epithelium (RPE).

"Standard photocoagulation with white burn endpoints is a supra-threshold, retina-damaging, laser surgery," he said. "The laser beam is not absorbed in the transparent retina, but in RPE and choroid melanocytes where light energy converts into heat. Heat spreads to the overlying neurosensory retina."

Sub-threshold photocoagulation is a laser therapy that works by inducing low temperature rises (5° to 15° C) around the RPE cells.

"With micropulsing, treatment can target the RPE more precisely and there is less risk of thermal spread that can cause unnecessary coagulative injury to surrounding retinal tissue," Dr. Rosen said.

User-friendly features

Previously available yellow lasers were argon-pumped dye laser systems that were large, had high electrical power demands, and were cumbersome to operate and maintain. The 577-nm solid-state laser offers the benefits of compact modern technology with additional design enhancements, including an easy-to-understand user interface, wireless foot pedal control with power adjust capability, audible confirmation of adjustments, and excellent visualization optics.

The fact that the laser can be attached easily and removed from a standard slit lamp is appreciated at the retina center of the NYEEI where avoiding the need to create a dedicated laser treatment room maximizes efficient use of the available space. This advantage has equal or greater importance for practices with a smaller office footprint, Dr. Rosen concluded.