SubLiminal® laser therapy can provide better treatment with lower risks for patients with retinal diseases and glaucoma, experts told delegates at a Quantel Medical Sponsored Symposium on SubLiminal® Laser Therapy, from Glaucoma to Retina Treatment at the recently held Asia-Pacific Academy of Ophthalmology Congress (APAO 2019) in Bangkok, Thailand.
“In the last 10 years, this area of subthreshold laser treatment has grown exponentially,” said Dr. Kenneth Fong, retinal surgeon, Sunway Medical Center, Malaysia. From treating retinal disorders, it can now also be used on glaucoma patients, added Dr. Fong, who has used a SubLiminal® retina laser for ten years.
Compared to conventional laser photocoagulation, the SubLiminal® subthreshold laser therapy by Quantel Medical (Cournon d’auvergne, France), does not use a continuous-wave laser beam and is non-thermal. Instead, it uses extremely short microsecond laser pulses followed by cooling time periods. This allows a high level of control over the thermal effect on targeted tissue. By using short enough laser pulses and long enough cooling times, the tissue can cool in between laser pulses, preventing damage and avoiding scarring while treating the retina. Using laser can reduce the burden of anti-VEGF injections in patients.
“Around the world, specifically in the Asia Pacific region, many countries cannot afford the continuous intravitreal injections. Patients can’t take it, and the governments and insurance companies can’t afford the cost of all the drugs you have to inject every few months, or every month or so into your patients’ eyes. So I believe that laser has a strong role in treating CSCR (central serous chorioretinopathy) and DME (diabetic macular edema),” explained Dr. Fong.
Subthreshold laser works by changing the microenvironment through retinal pigment epithelium (RPE) cells. There is no need to kill the RPE cells, but just enough energy is used to elicit a response. Subthreshold laser stimulation of the RPE leads to repair of the inner blood retinal barrier. Sublethal photothermal stimulation induces heat shock protein expression in RPE cells without cellular damage. Subthreshold means that visible changes cannot be seen during the procedure; and changes cannot be seen using current imaging technology.
With subthreshold laser, it is important not to undertreat patients, cautioned Dr. Fong. “There is a high risk of undertreatment in early cases,” he noted, adding that DME cases are often treated late with laser after failure with anti-VEGF and steroids. “Many times, patients with DME are referred to me after they have had many months of anti-VEGF or steroid treatment and a very chronic cystoid macular edema,” he explained. However, to date, there have been no randomized controlled trials comparing subthreshold laser versus anti-VEGF yet.
SubCyclo® Laser: A New Way to Treat Glaucoma
As a leading cause of irreversible blindness worldwide, glaucoma affects around 60.5 million people globally. Traditional glaucoma surgery carries risks, prompting doctors to wait until
it is necessary to perform glaucoma surgery but in the meantime the patients’ vision then deteriorates.
Dr. Nassima Benhatchi, Glaucoma Institute, Saint Joseph Hospital, Paris, France, talked about the interest of the SubLiminal® laser technology in enhancing cyclophotocoagulation procedures (SubCyclo®) for the treatment of advanced and end-stage glaucoma. Traditional cyclodestruction TSCPC (transscleral cyclophotocoagulation) employs a continuous wave with no cooling time, and tissue temperature builds up, causing damage in targeted and adjacent tissue, and sometimes results in severe complications. Side effects include initial high IOP (10%), uveitis (15-30%), chronic hypotony (1-15%), phthisis bulbi (0.5%-5%), and vision loss (30%), highlighted Dr. Benhatchi.
“Recently, another diode laser delivery mode has been used to treat glaucoma efficiently with more selective targeting tissue and less tissue damage,” she explained. The SubCyclo® laser therapy for intraocular pressure (IOP) reduction is a significant alternative in the treatment of glaucoma. It uses laser technologies that are not new, but new in its usage to treat glaucoma cases, especially in cyclophotocoagulation (CPC) therapy.
The SubCyclo® laser procedure for glaucoma is a non-thermal treatment for open-angle glaucoma and angle-closure glaucoma. It lowers IOP by stimulating the ciliary body and the uveoscleral pathway, without damaging effects.
Using extremely short microsecond pulses, this cyclophotocoagulation procedure lets surgeons precisely manage the thermal effect, while preserving the ciliary body structures. The use of ultrashort and repetitive pulses with rest periods, allows for tissue cooling times, as well as minimizes adjacent tissue damage. The ability to lower IOP safely, with the added advantages of speed and ease for patients and surgeons, makes this an exciting advancement in the treatment of glaucoma. It could offer benefits to patients, as surgeons often have to balance noncompliance with drugs versus invasive surgery.
“The daily treatment of glaucoma with drugs produces problems with compliance versus laser and surgery,” said. Dr. Benhatchi. A study was carried out from January to December 2017 to evaluate the efficacy, tolerability, side effects, and anatomical effects of SubCyclo® subthreshold cyclophotocoagulation comparing 25% and 31.3% duty cycles. It included all types of glaucoma, primary or secondary, advanced or moderate stage, as well as after failure of other therapeutics and high risk of surgery.
Indications for SubCyclo® laser included advanced stage of glaucoma after failure of other therapeutics, moderate stage of glaucoma, if filtration surgery presented too high a risk, intolerance to medication, palliative treatment or surgery failure, and in preparation for another surgery requiring an urgent IOP reduction such as cataract surgery. Topical prednisolone acetate 1% was prescribed 4 times a day for 1-2 weeks post-laser.
The study showed that in both groups treated by SubCyclo® laser, IOP reduction was statistically significant, at more than 20%, with no serious complications.
In conclusion, the use of SubCyclo® is found to have few complications, and no tissue damage, with a low rate of vision loss over time. Efficacy of the procedure was proven through clinical studies and practical experience. The treatment is fast, easy and repeatable if necessary. “My SubCyclo® experience is that it can be used in different stages of glaucoma and with different IOP levels,” Dr. Benhatchi said, adding that the 31.3% duty cycle is more efficient.
SubLiminal® Laser also Works on DME
A meta-analysis of the subthreshold laser for DME on 613 eyes from 11 studies, with 7 studies having a control group of 195 eyes treated with conventional laser, showed that no laser scar formation was seen with less than a 15% duty cycle, reported Dr. Kenneth Fong.
Overall, there was an increase in best corrected visual acuity (BCVA) and reduction in central retinal thickness (CRT) compared with conventional laser.
Types of DME suitable for SubLiminal® laser include those with clinically significant extrafoveal edema, and fovea-involving mild edema with good vision. In summary, SubLiminal® laser for DME works but doctors and patients must exercise patience as a perfectly performed laser takes from 6 to 12 weeks to show its effect.
Most published results show better visual acuity (VA) gains compared to a traditional style laser, noted Dr. Fong. Advanced targeting software allows accurate placement of burns. It is a cost-effective option and should not only be considered in rescue situations when anti-VEGF and steroids have failed.
Treating CSCR with SubLiminal® Laser
Conventional laser is effective for central serous chorioretinopathy (CSCR) but may damage the RPE and outer retina, said Professor Xiaoling Liu, Department of Retina, Wenzhou Medical University Eye Hospital, China.
SubLiminal® laser subthreshold treatment was a novel therapy for CSCR, she noted. A study was conducted to assess the efficacy and safety of 577nm SubLiminal® laser subthreshold treatment versus conventional laser treatment in CSCR. It concluded that SubLiminal® laser subthreshold treatment promotes the absorption of SRF effectively and improves visual acuity, she noted. It was non-inferior to conventional laser for improving BCVA at 12 weeks and has been found safer than conventional treatment.
Editor’s Note: The APAO 2019 Congress was held in Bangkok, Thailand, on March 6-9, 2019. Reporting for this story also took place at APAO 2019. Media MICE Pte Ltd, PIE Magazine’s parent company, was the official media partner at APAO 2019.
