New research published in Ophthalmic Physiological Optics investigated the use of low-level red light (LLRL) therapy for myopia, a form of treatment that has grown in popularity for pediatric patients, and its potential long-term drawbacks.
Give me some background first.
By now, it’s common knowledge that almost 50% of the global population is expected to have myopia by 2050.
Though this seems inevitable, more treatment options are becoming increasingly available as investigators and clinicians seek to take a proactive treatment role in identifying and managing myopia to mitigate profession earlier in the disease state process.
One of these options is LLRL therapy, an emerging therapy that, based on previous research, could potentially and significantly reduce myopia progression in children over a 6-month period when used at 100% power (compared to a sham device with 10% original power).
Explain this LLRL therapy further.
Also known as repeated LLRL therapy or photobiomodulation, LLRL therapy is a novel treatment conducted via devices (tabletop or wearable headsets) that emit red laser light for the sole purpose of controlling myopia.
The therapy is conducted in twice-daily, 3-minute sessions in pediatric myopic patients until they reach the end of their teenage years.
Based on previous research, it’s been proven to slow myopia by up to 80%—compared to 30% and 60% for spectacles and contact lenses, respectively.
I’m sensing a ‘but’ here…
But of course. While appearing to be an effective option for myopia, LLRL therapy’s safety profile and long-term effect still remains unclear—a fact that investigators sought to explore further.
Which leads us to this research?
Indeed it does. Researchers obtained two LLRL tabletop devices from two different manufacturers:
- Sky-n1201a (Beijing Akihito Vision, Vision Technology Co., Ltd.)
- Future Vision (Hunan Medical Technology Co., Ltd)
The researchers performed optical power measurements using an integrating sphere radiometer through a 7-mm diameter aperture, in accordance with ANSI Z136.1-2014, sections 3.2.3-3.2.4 (more on that in a moment).
They also obtained retinal spot sizes using a model eye and high-resolution beam profiler.
Of note: Both are Class 1 laser devices with a similar safety profile classification to that of a laser pointer.
Define a Class 1 laser.
According to the FDA, lasers range from Class 1 (non-hazardous) to Class IV (most hazardous).
Class 1 low-powered devices are considered generally safe from all potential hazards; laser printers and CD players are model examples of this classification.
Gotcha. So what was measured?
For each device:
- Optical measurements
- Corneal irradiance
- Retinal irradiance
- Retinal spot size
- Maximum permissible exposure (MPE)
- Photochemical damage
- Time needed to reach a retinal radiant exposure of 50 J/cm2
- Thermal damage
- Photochemical damage
And the findings?
Sky-n1201a
- Wavelength = 654 nm
- Power = 0.2 mW (Ø 7 mm aperture at 10 cm distance)
- Illuminance 310 lux (at the cornea)
- Corneal irradiance = 1.17 mW/cm2
- Retinal irradiance = 7.2-88.2 W/cm2 (Ø 2–7 mm pupils)
- Retinal spot
- Circular spot: 11 x 11 μm2
- Point source
- Circular spot: 11 x 11 μm2
- MPE
- Photochemical damage = 0.55–7 s for 2–7 mm pupils
- Thermal damage = 0.41–10 s for 4.25–7 mm pupils.
Future Vision
- Wavelength = 652 nm
- Power = 0.06 mW (Ø 7 mm aperture at 10 cm)
- Illuminance = 100 lux (at the cornea)
- Corneal irradiance = 0.624mW/cm2
- Retinal irradiance = 0.08–0.97 W/cm2 (Ø 2–7 mm pupils)
- Retinal spot
- Elliptical spot: 240 x 250 μm2
- 0.75 × 0.325° extended source
- Elliptical spot: 240 x 250 μm2
- MPE
- Photochemical damage = 50–625s for 2–7mm pupils.
Tell me more.
The study authors noted that, for the Sky-n1201a, “viewing the laser with pupil diameters less than 4.25 mm did not put a user at risk for thermal damage,” and that, “The Future Vision does not put the retina at risk of thermal damage.”
For both lasers, 3 minutes of continuous viewing surpassed the luminance dose MPE, “putting the retina at risk of photochemical damage,” they wrote.
That’s not good, is it?
No, it’s not. There are American National Standards Institute (ANSI) standards for ophthalmic-based instrumentation, which specifically address safety requirements for ophthalmic equipment examining the minimum acceptable thresholds for direct optical radiation into/at the eye.
Subsequently, ANSI recommends that, after reaching the MPE, light of similar intensity should not be viewed for at least 48 hours, according to the study. “However, in the case of LLRL therapy, children are instructed to view his high-intensity laser light twice within 24 (hours) and repeated daily for the duration of the treatment period, which could be several years,” the investigators stated.
Expert opinion?
Based on their findings, the authors wrote that, “it is recommended that clinicians strongly consider the use of LLRL therapy for myopia in children until safety standards can be confirmed.”
They advised that the ANSI standards be carefully reviewed for ophthalmic laser devices to ensure the retina isn’t placed at further risk for photochemical damage, especially given that the treatment group is a pediatric population.
Additionally, the authors called for future research on this subject to include “high-resolution imaging and more advanced functional testing to assess retinal integrity.”