Title: Effects of mild-and moderate-intensity illumination on axial length and choroidal thickness in young adults
Authors: Ranjay Chakraborty (1), Konogan Baranton (2), Daniel Spiegel (3), Pascale Lacan (2), Matthias Guillon (2), Nicola Anstice (1), Coralie Barrau (2), Thierry Villette (2)
- Discipline of Optometry and Vision Science, College of Nursing and Health Sciences, Flinders University, Adelaide, South Australia
- Centre for Innovation & Technologies Europe, Essilor International SAS, Paris, France
- Essilor Centre for Innovation & Technologies, Essilor Amera Pte Ltd., Singapore
Reference: ARVO 2021 abstract and video presentation
Previous research in animal models has shown that where developing eyes have been exposed to light, it gives a dose-response protective effect against developing myopia. Similarly, outdoor time in children seems protective against myopia with a duration-response effect.
In this study, 15 young adults wore light-emitting glasses in a dark room for 120 minutes. The glasses emitted diffuse white light 4cm in front of the eyes, and participants watched a colour muted television at 5m during the experiment. After 60 minutes of exposure, axial length reduced and choroidal thickness increased, each by around 20 microns (0.02mm) compared to darkness. Full recovery of changes occurred after 30 minutes, and there was no difference found between a 500 lux and 1000 lux setting, although 1000 lux seemed to have a slightly larger effect.
What does this mean for your clinical practice? Firstly this indicates a beneficial physiological change in the eye with exposure to light, and hence we should continue to advocate for increased outdoor time in our young patients, especially pre-myopes. Secondly, this raises the interesting concept of controlled exposure through light-emitting glasses, where time spent outdoors is more difficult due to weather, for example - but since the participants were looking at distance throughout the experiment, the interaction between viewing distance and the beneficial light effect is unknown.
Purpose: Rearing under high-intensity illumination produces a hyperopic shift in chicks and inhibits the development of form-deprivation myopia in chicks and primates. Recent studies also show that time spent outdoors is protective against the development of myopia in children. In this study, we examined the effects of 120 minutes of exposure to 500 and 1000 lux of bright illumination on axial length and choroidal thickness (ChT) in young adult participants.
Methods: Fifteen participants (mean age, 21.60 ± 2.16 years) with a mean refraction of -0.30 ± 0.39D were exposed to 500 (142 μW/cm2) and 1000 (284 μW/cm2) lux of illumination for 120 minutes in a dark room on two different days, using a pair of custom-made light-emitting glasses. On each day, a series of ocular measurements were performed in the left eye before the light exposure (0 minutes), at 30, 60 and 120 minutes of light exposure, and 30 minutes after light offset to measure recovery. All ocular measurements were repeated on a third measurement day without any light stimulus in darkness (~ 5 lux). Axial length was measured using the Lenstar optical biometer and the changes in the subfoveal ChT were measured using Cirrus 5000 optical coherence tomographer. Measurements are reported as mean ± standard error mean and statistical comparisons were made using two-way ANOVA.
Results: Axial length increased significantly across all time points in darkness. Exposure to 500 and 1000 lux of continuous illumination resulted in a gradual and significant reduction in axial length at 30, 60 and 120 compared to darkness (change in axial length at 60 minutes: darkness, +0.014 ± 0.003mm; 500 lux, -0.007 ± 0.002mm; 1000 lux -0.010 ± 0.004mm, p<0.01). Exposure to 500 and 1000 lux of illumination caused a significant thickening of the choroid (change in ChT at 60 minutes: darkness, -0.011 ± 0.006mm; 500 lux, +0.006 ± 0.003mm; 1000 lux +0.008 ± 0.004mm, p=0.025). None of the ocular changes were significantly different between the 500 and 1000 lux illumination levels (p>0.05). All ocular changes recovered to normal within 30 minutes of light offset.
Conclusions: Our results show that exposure to mild- or moderate-intensity illumination can induce a significant reduction in axial length and thickening of the choroid in young subjects. Similar to animal models, these changes were found to be sensitive to the duration of light exposure.
Disclosure block: Ranjay Chakraborty, Essilor International (Code F (Financial Support)); Konogan Baranton, Essilor International (Code E (Employment)); Daniel Spiegel, Essilor International (Code E (Employment)); Pascale Lacan, Essilor International (Code E (Employment)); Matthias Guillon, Essilor International (Code E (Employment)); Nicola Anstice, None; Coralie Barrau, Essilor International (Code E (Employment)); Thierry Villette, Essilor International (Code E Employment))
Ailsa Lane is a contact lens optician based in Kent, England. She is currently completing her Advanced Diploma In Contact Lens Practice with Honours, which has ignited her interest and skills in understanding scientific research and finding its translations to clinical practice.