Intravitreal anti-VEGF therapy is the first-line treatment for DME. A laser treatment within the clinical setting, however, can be effective in many situations. In the DRCR.net Protocol T, between 40% and 60% of patients who received nine or 10 anti-VEGF injections in the first year of the study had a history of laser therapy.1
Conventional laser systems use a small spot size, which causes retinal atrophy and thinning in the areas of the laser application. Subthreshold lasers are now used routinely for many retinal diseases and use a train of microsecond pulses combined with a large spot size. They have proven efficacy without showing any visible signs of damage to the eye of the examiner.2
SUBTHRESHOLD LASER TYPES
There are three types of modern subthreshold lasers.
SubLiminal. This type of laser is used for Subthreshold Laser Therapy treatment. It is based on the emission of short repetitive pulses that last for microseconds, allowing significant cooling of the tissue between the pulses.
Endpoint management. This type of laser provides continuous energy delivery with decreased power levels and duration in attempt to achieve no visible scarring.
Nanosecond laser. This type of laser has similar specifications to those used for selective laser trabeculoplasty.
Modern subthreshold lasers can be titrated and customized by varying power settings, shortening the pulse duration, and using pulses to achieve a targeted endpoint. For DME and CSR, I use SubLiminal Laser Therapy with a 5% duty cycle, 160-µm spot size, and a 200-millisecond duration in a confluent pattern. For the former, an OCT thickness map is used to visualize the macular thickness. For the latter, a fluorescein angiogram is used to identify the areas of leakage.
LASER GUIDELINES
The Subthreshold Ophthalmic Laser Society (SOLS) has published laser guidelines for retinal diseases. The society recommends the use of a 5% duty cycle, 200-millisecond pulse duration, between a 150- to 200-µm spot size, and no spaces between the spots.
The laser energy must be titrated prior to treatment. Once the threshold power level is identified, 50% of it is used for the treatment of the thickened areas for DME or the hotspots for CSR (Figure).
REDUCE PATIENT APPOINTMENTS
Anti-VEGF therapy is demanding. Many patients with DME can’t keep up with their injections. I find that supplementing anti-VEGF therapy with subthreshold laser treatments can reduce their visits to the clinic.
I usually perform one anti-VEGF treatment to reduce the edema and supplement it with a subthreshold laser treatment. A lot of patients don’t require further injections after about 3 to 6 months of the combined treatment strategy.
CONCLUSION
SubLiminal Laser Therapy does not show any visible signs of damage to the eye.2 It can be used as a standalone treatment as well as an adjunct therapy for patients with DME.
1. Wells J, Glassman A, Ayala A, The Diabetic Retinopathy Clinical Research Network. Aflibercept, bevacizumab or ranibizumab for diabetic macular edema. N Engl J Med. 2015;26;372:13:1193-203.
2. Chong V. How new generation lasers are different from each other? Ophthatherapy. December 2018. Accessed November 16, 2023. https://www.journalsmededu.pl/index.php/ophthatherapy/article/view/542
