Radiometric and safety assessment of a 'low-level red-light' myopia control device

Recent literature has demonstrated that 'low-level red-light therapy' may be effective at slowing axial elongation in children, but reports have questioned the safety of some red-light devices. The current work explored the beam characteristics and hazard potential for a myopia control red-light device.

The optical design and exiting beam characteristics of a sample red-light myopia control device (SECONEE sky-n1201a) were quantified by measuring beam divergence and total flux passing through artificial pupils of 1-9 mm diameter placed at the corneal plane. Retinal exposure levels were compared to American National Standards Institute (ANSI) limits for ophthalmic instruments (Z80.36-2021).

Two 655 nm laser diodes created exiting red-light beams (~9 mm in diameter) that were approximately collimated by an internal pair of +10.00 D eye-piece lenses resulting in exit vergences ranging from -3.25 to -7.75 D as interpupillary distance settings were adjusted from 52 to 70 mm. Radiant power (mW) passing through the artificial pupils increased from 0.005 to 0.65 mW as pupil diameters increased from 1 to 9 mm. Using ANSI Z80.36-2021, time-averaged retinal radiant exposures (J/cm²) exceeded the thermal and photochemical limits for pupil diameters >1 mm and >5 mm, respectively. The time to reach potential photochemical radiation hazard (t_max) was less than 100 s for pupil diameters >5 mm.

The optical design and resulting beam characteristics of this sample red-light myopia control device generate retinal exposure levels that vary with pupil diameter, accommodation and eye movements. Conservative estimates reveal retinal radiant exposures that can exceed ANSI safety limits. The 'low-level' moniker is inappropriate for a device that either exceeds or is just below the ANSI threshold for potential retinal hazard.