FOCUS ON …
TxCell Scanning Laser Delivery System
BY JEFFREY S. EISENBERG
While the Early Treatment Diabetic Retinopathy Study (ETDRS) established conventional thermal macular photocoagulation as the standard of care for DME, it also found the incidence of adverse effects increased with laser intensity.1 Complications included inadvertent foveal photocoagulation, exacerbation of macular edema due to inflammation, retinal fibrosis, CNV, visual field loss, color vision loss, metamorphopsia, and expansion of laser scars to the fovea.1
For these reasons, Sam Mansour, MD, a clinical professor of ophthalmology at George Washington University, Washington, DC, prefers using subthreshold MicroPulse Laser Therapy (MPLT) for treating DME. MPLT delivers less energy than conventional treatment, and has been shown to be as effective in stabilizing visual acuity and reducing macular edema, with the benefit of no postoperative tissue damage with significant improvement in retinal sensitivity.2
MicroPulse technology electronically “chops” a continuous wave (CW) laser emission into tiny trains of repetitive microsecond pulses, each followed by brief rest periods. This allows the user to more precisely control the laser effects on target tissues.
“There is an interval where the tissue can cool … so it’s not irreversibly damaged,” Dr. Mansour says. “By doing that, you’re not only preventing tissue damage; you’re also photostimulating the RPE cells.”
Dr. Mansour used his first Iridex laser in the 1990s. More recently, he started using the TxCell Scanning Laser Delivery System (Iridex Corp., Mountain View, Calif.), which received FDA 510(k) and CE clearance in December 2012.
THREE TREATMENT CHOICES
The TxCell can be combined with the Iridex green (IQ 532) and yellow (IQ 577) lasers.This combination allows use of multi-spot pattern scanning, single-spot standard, and MPLT. Confluent, multi-spot laser patterns are ideal for MPLT because more treatment spots than CW are necessary due to its limited thermal spread.
A prospective, double-masked, controlled trial on 123 eyes with DME compared modified ETDRS laser photocoagulation with normal-density or high density (confluent) subthreshold MPLT.3 At one-year follow-up, the study found high density MPLT superior to modified ETDRS, based on anatomic and functional measures of improvement.
Another difference: In a CW laser, once you fire the spot, you can see visible changes in the tissue. Not so with MPLT. “Target Cell” technology, exclusive to TxCell, allows visualization of the treated tissue by identifying the perimeter of the targeted area. Three patterns are available: grid, circular and triple arc.
“The TxCell makes it a lot easier, because it projects a visible grid to show us where the laser has been fired,” Dr. Mansour says. “And, you can actually see as you press the pedal, the aiming beam moving across the treated area like a sewing machine.”
The Iridex TxCell scanning laser system delivers three treatment modalities, including MicroPulse Laser Therapy.
EASE OF USE
The TxCell scanning laser has a short learning curve, according to Dr. Mansour. Iridex provided field representatives to guide him through the first few treatments.The company also has a series of online videos on MPLT. RP
1. Luttrull JK, Dorin G. Subthreshold diode micropulse laser photocoagulation (SDM) as invisible retinal phototherapy for diabetic macular edema: a review. Curr Diabetes Rev. 2012;8:274-284.
2. Vujosevic S, Bottega E, Casciano M, Pilotto E, Convento E, Midena E. Microperimetry and fundus autofluorescence in diabetic macular edema: Subthreshold micropulse diode laser versus modified Early Treatment Diabetic Retinopathy Study laser photocoagulation. Retina. 2010;30:908-916.
3. Lavinsky D, Cardillo JA, Melo LA Jr., Dare A, Farah ME, Belfort R Jr. Randomized clinical trial evaluating mETDRS versus normal or high-density micropulse photocoagulation for diabetic macular edema. Invest Ophthalmol Vis Sci. 2011;52:4314-4323.