Revisiting the Roles of Lasers in Retina

New technologies call into question some assumptions regarding the use of laser.

By Margaret Wong, MD
 

Traditional laser photocoagulation has become a less desirable option in recent years, as it is inherently destructive to retinal tissue. However, new laser systems seem to be changing this paradigm, providing treatment only to desired areas with little or no damage to adjacent areas.

For example, micropulse laser therapy, described by Friberg and Karatza in the 1990s,1 is a tissue-sparing technique in which a continuous-wave diode laser beam is split into a series of repeated low-energy pulses, interrupted by brief rest periods that allow tissues to cool. Performing laser in this manner reduces destructive thermal energy delivery to the treated area, thereby mitigating destructive potential. Diode lasers offering micropulse mode are available from Iridex and Optos.

RETHINKING TREATMENT

In a clinical trial in individuals with center-involving clinically significant diabetic macular edema (DME), micropulse laser was as effective as modified Early Treatment Diabetic Retinopathy Study (mETDRS) focal/grid laser photocoagulation in stabilizing visual acuity and reducing macular edema at 1 year, while causing no detectable tissue damage.2 Micropulse laser treatment causes upregulation of a number of antiangiogenic and restorative biologic factors that help to repair the retinal architecture.3-5

Figure 1. Optical coherence tomography (OCT) before (A,B) and after (C,D) treatment with micropulse laser therapy in the right and left eyes, respectively.

I added micropulse laser with the IQ 577 (Iridex) to my practice because it expands my treatment options for DME and for macular edema secondary to uveitis and retinal vein occlusion (RVO), especially for edema near or in the fovea. Using this mode, I have learned that I can trust myself to apply laser to the fovea—something that would be forbidden with traditional laser. The safety of foveal application is supported by authors of a study using Iridex 810-nm, 577-nm, and 532-nm wavelength lasers.6

Retina surgeons are trained to trust what we see when it comes to laser. A laser spot is classically considered effective if a burn is evident, and, therefore, the treatment area and number of spots should be minimal. The application of micropulse laser runs counter to this doctrine, as the laser spots are either minimally visible or invisible after application.

With micropulse, better results are achieved with a large volume of spots—between 500 and 700 in a single treatment. Again, the science supports this notion, and it requires rethinking one’s treatment strategy. A prospective, double-masked, controlled clinical trial including 123 eyes with DME compared three dosing protocols: mETDRS, low-density micropulse, and high-density micropulse.7 At 1 year follow-up, patients in the high-density micropulse group had the greatest improvements on optical coherence tomography (OCT; -154 µm reduction in central thickness vs. -126 µm for mETDRS vs. -32 µm for low-density micropulse) and in BCVA (+12 vs. +4 for mETDRS vs. -1 for low-density micropulse). In the high-density micropulse group, 48% of patients gained 15 letters or more, compared with 23% in the mETDRS group and 5% in the low-density micropulse group.

CASE REPORTS

One of the benefits of micropulse laser is that it can be used as an adjunct to or replacement for intravitreal injections for treatment of macular edema. I have used micropulse in a number of patients who could not tolerate steroids, who were not deriving benefit from anti-VEGF therapy, or who had plateaued on medical therapy.

Two cases serve to demonstrate the benefits of micropulse laser as an adjunct to medical therapy.

Figure 2. OCT shows improvement in macular edema after micropulse laser therapy. Before treatment (A) and after treatment (B).

Case No. 1

A 61-year-old Caucasian man had DME in both eyes (OU); previous treatments included traditional focal laser OU. Visual acuity was 20/20 in the right eye (OD) and 20/400 in the left (OS). The patient was started on intravitreal triamcinolone acetonide (Triesence, Alcon) OS and ranibizumab (Lucentis, Genentech) OU. These efforts led to maintenance of 20/200 vision OS for 2 years. In November 2014, I applied micropulse laser OU, and the patient had two treatments OD and three treatments OS over the next 2 years, with intravitreal ranibizumab injections in between. Visual acuity was maintained at 20/20 OD and improved to 20/100 OS (Figure 1). The patient states subjectively that he feels there has been significant improvement in both eyes since initiating micropulse treatments.

Case No. 2

A 50-year-old African-American woman with chronic uveitis and cystoid macular edema (CME) OU was a known steroid responder. Her visual acuity was count fingers OD and 20/50 OS. End-stage hypotony limited treatment options OD. Bevacizumab (Avastin, Genentech) administered OS partially treated the CME, and visual acuity improved to 20/40 in this eye. Micropulse laser was performed 5 months after bevacizumab injection, and visual acuity OS improved to 20/25. There was no recurrence of CME after 1 year (Figure 2).

CONCLUSION

Adding micropulse laser therapy to my practice has increased my laser volume by more than 25% and has had a positive effect on patient care. It is a gentler way of performing laser that adds benefit to the practice because it is a versatile treatment option that can reduce the need for pharmacotherapy and provide additional benefits.

1. Friberg TR, Karatza EC. The treatment of macular disease using a micropulsed and continuous wave 810-nm diode laser. Ophthalmology. 1997;104(12):2030-2038.

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(6):908-916.

3. Ogata N, Tombran-Tink J, Jo N, Mrazek D, Matsumura M. Upregulation of pigment epithelium-derived factor after laser photocoagulation. Am J Ophthalmol. 2001;132(3):427-429.

4. Binz N, Graham CE, Simpson K, et al. Long-term effect of therapeutic laser photocoagulation on gene expression in the eye. FASEB J. 2006;20(2):383-385.

5. Yu AK, Merrill KD, Truong SN, Forward KM, Morse LS, Telander D. The comparative histologic effects of subthreshold 532- and 810-nm diode micropulse laser on the retina. Invest Ophthalmol Vis Sci. 2013;54(3):2216-2224.

6. Luttrull JK, Sinclair SH. Safety of transfoveal subthreshold diode micropulse laser for fovea-involving diabetic macular edema in eyes with good visual acuity. Retina. 2014;34(10):2010-2020.

7. 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(7):4314-4323.

Margaret Wong, MD
• uveitis and vitreoretinal specialist, Eye Consultants of Atlanta
• financial interest: none acknowledged
margaret.oph@gmail.com

 

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About New Retina MD

New Retina MD delivers cutting-edge content to retina specialists in their first 15 years of practice. Each issue provides fresh insight from younger physicians plus established mentors on clinical and nonclinical issues affecting ophthalmologists in the earlier stages of their careers. NRMD features surgical pearls, clinical research endeavors, practice management, medical reimbursement and policy, continuing educational requirements, financial planning, innovations, and more.