Light-based therapies are gaining traction in myopia control, but a fundamental question remains: how much of that light reaches the target tissues within the eye? A new experimental study by researchers at the University of Houston College of Optometry, Houston, Texas, provides important insight, revealing striking differences in how red and violet wavelengths penetrate ocular structures.
Using freshly enucleated porcine eyes, the researchers measured transmission of red laser light, red LEDs, and violet LEDs through individual ocular tissues – including the cornea, lens, retina, retinal pigment epithelium (RPE)/choroid, and sclera. This tissue-level approach allowed precise quantification of how light is attenuated as it passes through the eye.
The findings were clear: red light consistently demonstrated greater transmission than violet light across anterior and posterior structures. Corneal, lenticular, and retinal transmission were all significantly lower for violet LEDs compared with both red laser and red LED sources.
The lens emerged as a key barrier to shorter wavelengths. Violet light was strongly attenuated before reaching the retina, with only around two-thirds of incident light transmitted to this level. In contrast, red light showed far higher penetration, with the majority reaching the retina and substantial proportions continuing to the RPE/choroid.
However, regardless of wavelength, very little light from these therapies reached the sclera. The study revealed that less than 1% of incident light reached this posterior structure across all light sources examined.
These findings have direct relevance for emerging light-based interventions, such as repeated low-level red light (RLRL) therapy and violet light exposure. Red light therapies have demonstrated strong clinical efficacy in slowing myopia progression, with reported reductions in axial elongation of up to 60–80% in schoolchildren.
Yet the mechanism of action remains debated. One proposed pathway is direct photobiomodulation of the sclera. The current data challenge this assumption: if less than 1% of light reaches the sclera, it raises questions about whether this tissue is the primary therapeutic target.
Instead, the study authors suggest that retinal and choroidal pathways may play a more prominent role. Greater light delivery to these tissues supports mechanisms involving dopamine signaling, mitochondrial activity, and choroidal blood flow regulation.
For violet light therapies, the picture is different. Although clinical and preclinical studies suggest a protective effect – potentially mediated by retinal photopigments such as OPN5 – the strong attenuation by the cornea and lens may limit effective retinal exposure, particularly in older patients.
The study also highlights differences between light sources. Red LEDs achieved transmission levels comparable to red lasers, suggesting they may offer a safer alternative without compromising tissue penetration. This is particularly relevant given concerns that some red laser devices may approach or exceed safety limits for retinal exposure.
The findings underscore the importance of understanding not just the wavelength, but the delivery characteristics of light-based devices. Factors such as beam profile, intensity, and exposure duration will all influence therapeutic outcomes.
As interest in non-invasive myopia therapies continues to grow, this study provides a crucial piece of the puzzle – linking device output to actual tissue exposure. The results suggest that future therapies may benefit from targeting retinal and choroidal pathways rather than the sclera, and from optimizing wavelength and delivery to maximize efficacy while maintaining safety.
