In this time of uncertainty, one thing is certain (at least in ophthalmology): Retinal pathologies are not going anywhere.
In fact, chronic conditions like age-related macular degeneration (AMD) and diabetic retinopathy (DR) are thought to be causing more concerns during this period of worldwide lockdown and social distancing. Either out of safety concerns, or because their doctor’s practice is closed, some patients are not visiting clinics for screening, diagnosis, monitoring or treatment — all of which can lead to sight-threatening vision loss.
As a result, laser is stepping up as a popular (yet, perhaps underutilized) treatment modality for retinal pathologies. Indeed, doctors and patients alike are turning toward laser to reduce repeated in-person office visits — which are required for effective anti-vascular endothelial growth factor (VEGF) treatment.
To learn more, Quantel Medical, an ophthalmic laser manufacturer based in Cournon-d’Auvergne, France, sponsored a recent webinar called Modern Laser Therapy for the Treatment of Retinal Diseases, which addressed the benefits of laser from two retinal specialists, Drs. Kenneth Fong and Victor Chong.
Peripheral Treatments: Best Cases for Laser
Now that patients are making fewer visits to eye clinics, Dr. Fong, from OasisEye Specialists in Kuala Lumpur, Malaysia, suggests that retinal laser should be considered to reduce further risk in patients with diabetic retinopathy (DR) and associated conditions.
While Dr. Fong notes that the older versions of PRP (panretinal photocoagulation) could cause severe anatomical damage to the peripheral retina, he says the newer PRP has several benefits. “It’s really considered a cure,” said Dr. Fong. “Thanks to multi-spot laser technology, we can complete the entire PRP treatment in one session, without the need for further anti-VEGF injections.”
“Given the chronic nature of proliferative diabetic retinopathy (PDR) and the intravitreal half-life of anti-VEGF drugs currently in use, the main disadvantage of anti-VEGF monotherapy for PDR is that these drugs need to be administered periodically,” said Dr. Fong. “Interruption of treatment can be catastrophic and may lead to irreversible blindness.”
Macular Laser: Comparing Apples and Oranges
Not all lasers are created equal — and as the technology has advanced so has the understanding in regard to safety and efficacy. And indeed, finding the balance between delivering more energy, but with less anatomical damage, is crucial to positive outcomes.
From conventional laser, the evolution to Endpoint Management (PASCAL; Topcon, California, USA) decreased the power and duration, said Dr. Chong, from London Medical and the Royal Free Hospital in London.
“However, this modality offers a very small therapeutic window, so you have to be very precise: Too much energy and there is damage, too little and you cannot see the benefits.”
Additionally, this modality shows scarring on optical coherence tomography (OCT), fundus fluorescein angiography (FFA) and autofluorescence (AF).
“This is why, for many years, we have been working on a system that can deliver more energy with less damage thanks to a pulsed laser delivery mode,” he said. “The good thing about SubLiminal is that you don’t kill any cells — or at least you aim not to.”
Meanwhile, the SubLiminal laser from Quantel Medical has the energy to target the RPE and is effective without scarring on OCT, FFA and AF. Thus, according to Dr. Chong, SubLiminal threshold laser may hold the key. “We have previously published that using this type of methodology improves retinal sensitivity and reading speed,” he shared, adding that there are multiple papers on the safety and efficacy of SubLiminal laser.
“SubLiminal laser has a long track record, and over the years we have improved the protocol and we can show the clinical benefit,” shared Dr. Chong.
He also briefly discussed the selective retinal therapy laser (2RT; Nova Eye, California, USA), which he noted has a very short duration of 3 nanoseconds. However, it can also produce some scarring, which can be seen on OCT, FFA and AF.
Digging Deeper into SubLiminal Laser Therapy
Dr. Fong helpfully summed up the SubLiminal laser treatment guidelines as follows: 577 nm wavelength; 160 µm spot size; 5% duty cycle; 0.2 second exposure time. Since there is no intended thermal injury using SubLiminal laser, “the key is doing a dense treatment, using a large spot size of 160 µm,” explained Dr. Fong, adding that the most important step is power titration, as every patient is different. “Once the thermal threshold is achieved, the power should be reduced by 50%, and then the laser should be performed,” he said.
As far as efficacy, SubLiminal laser is ideal for patients with non-center involving macular edema because those areas can be treated easily. “For those with fovea-involving, I would usually give anti-VEGF first to reduce the thickness, and then I would supplement it with laser. At one month after anti-VEGF, we are ready to treat the remaining thickened areas, avoiding the fovea at all times.”
SubLiminal laser treatment can also be used in chronic CSC (central serous chorioretinopathy) and is an alternative to mid-fluence PDT (photo dynamic therapy) in first-line treatment.
“For DME patients, I just use an OCT thickness map,” he continued. “For patients with CSC, you need indocyanine green angiography (ICGA) for complex cases or FA-guided (for simple cases) because it’s important to be precise of where you are treating.”
So, how long does it take to see improvement following treatment? For DME patients, it takes a minimum of about 3 months; for CSC, the result is much faster, at about 6 weeks.
Expanding Clinical Applications
According to Dr. Chong, SubLiminal laser therapy may be trending toward increased uptake. The therapy is already established as effective and safe for treating DME and CSC. It can also be used in branch retinal vein occlusion (BRVO) — although in some cases of BRVO it doesn’t always work, so it can be a supplement to anti-VEGF, noted Dr. Chong.
It has also been effective with macroaneurysms, but it is not applicable in cases of PDR for which multispot laser is the treatment of choice, he explained. It could also possibly be an option for nAMD patients who are nonresponsive to anti-VEGF. “SubLiminal technology might be able to revitalize RPE cells and make them more responsive to anti-VEGF treatment,” shared Dr. Chong.
There is some evidence that SubLiminal laser could work in PCV (polypoidal choroidal vasculopathy), but it would likely need anti-VEGF in combination. “But if you catch some of the earlier polyps with laser, then that certainly seems to work,” he continued.
Regarding applicability to drusen, Dr. Chong said that they are working on a study — but it’s currently on hold due to COVID-19, with plans to resume in the fall. However, he did point to some other smaller studies, one of which found that out of 30 cases, drusen load was reduced in 20 using SubLiminal laser.
“In summary, I think it’s very clear that in DME and CSC patients, it works. In BRVO and macroaneurysm, it seems to work — and it could possibly work in PCV and drusen. But, I don’t think it works in PDR,” concluded Dr. Chong.
Editor’s Note: The webinar, Modern Laser Therapy for the Treatment of Retinal Diseases, sponsored by Quantel Medical, was held on 22nd June 2020. Reporting for this story also took place during the said event. A version of this article was first published in PIE Issue 15 (ebook version).