Abstract
Purpose :
Low level red light laser (LLRL) therapy is an emerging treatment for myopia that shows promising results in published studies. In LLRL, children are instructed to look into an instrument emitting a red laser for 3 minutes twice a day, 5 days a week, for the duration of the treatment period, which could be on the order of years. Numerous devices are currently available and actively used in China. However, the safety profile of these devices has not been fully investigated. The goal of this study was to characterize the output and determine thermal and photochemical maximum permissible exposure time for two different red light devices being used for myopia control.
Methods :
LLRL devices from two different manufacturers were obtained. For each device, power was determined through a 7 mm aperture by placing the sensor of a radiometer 10 cm from the output of the source. Corneal and retinal irradiance were calculated. ANSI Z136.1-2014 standards were used to determine laser class, and luminance dose restrictions (Morgan, 2008; ANSI Z136.1-2014, 8.3.3.) were applied to calculate maximum permissible exposure time (DeLori, 2007).
Results :
Both devices were determined to be Class 1 and within the safety limits for thermal damage. Figure 1 shows the maximum permissible exposure time using the luminance dose restrictions outlined in section 8.3.3. ANSI 2014, which states that any exposure over 100 seconds must be less than 5 J/cm2/V(λ) to avoid photochemical damage to the retina. Device 1 was measured to have a wavelength of 654 nm, power of 0.2 mW (Ø7 mm, 10 cm away), corneal irradiance of 0.52 mW/cm2, and retinal irradiance of 3.2 W/cm2. The maximum permissible exposure time for a 2 mm pupil was 31.3 s and for a 7 mm pupil was 2.3 s. Device 2 had a wavelength of 652 nm, power of 0.06 mW, corneal irradiance of 0.156 mW/cm2, and retinal irradiance of 0.96 W/cm2. The maximum permissible exposure time for a 2 mm pupil was 104.2 s and for a 7 mm pupil was 8.51 s.
Conclusions :
The two different LLRL devices examined were found to be Class 1 and within the safety limits for thermal damage. However, luminance dose restrictions suggest that maximal permissible exposure time for direct viewing is 2-104 seconds, depending on device and pupil size. Therefore, 3 minutes of continuous viewing surpasses maximal permissible exposure time, putting the retina at risk for photochemical damage.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.