Intermittent exposure to illuminances of 5500 lux considerably prevents myopia development and increases scleral stiffness in chicks

Abstract

Purpose : To investigate the illuminance-dependent impact of intermittent and continuous light on form-deprivation myopia (FDM), scleral stiffness, and retinal proteomics in chicks.

Methods : FDM was induced in one eye (FD eyes) from day 1 post-hatching (D1) until D8 in 7 groups of 9-13 chicks each. The fellow eye was used as uncovered control. All groups were raised under standard white light (SL, 286 lux, 7am-7pm). Six groups were additionally exposed to 4h/day of intermittent (IL: 1h every 2h of SL starting at 8am, 3 groups) or continuous (CL: 4h centered at 12pm, 3 groups) white light of distinct illuminances (~1500, ~5500 and ~10000 lux). One group was left untreated (SL). Axial length (AL), refraction, and choroidal thickness (CT) were measured on D1 and D8. After euthanization (D9), the retinas and posterior scleras were collected for proteomics and biomechanical analyses, respectively. In-vivo data from D8 were expressed as inter-ocular difference (IOD=FD-control eye) and compared using a 2-way ANOVA. Scleral stiffnesses were compared using a 1-way ANOVA.

Results : Compared to control eyes, untreated FD eyes had increased AL (0.79±0.19mm), myopic refraction (-8.34±0.93D), and choroidal thinning (-75.3±48.0µm) (all P<0.001). IL and CL alleviated these changes in an illuminance-dependent manner (all P<0.001) with 10000 lux of IL or CL fully stopping FDM. At 1500 lux, CL was better than IL in reducing axial elongation (P<0.001) and increasing CT (P<0.01). However, IL was overall better than CL in reducing myopic refraction (P<0.001), and 5500 lux of IL was over 2-fold more effective than CL in reducing myopic refraction (P<0.001, Fig 1B), in addition to reducing AL (P<0.05). At 5500 lux, the tangent modulus at 1% strain of scleras exposed to IL was increased compared to CL and SL (P<0.01, Fig 1D), and the retinas of FD eyes exposed to IL or CL showed distinct proteomic profiles on principal component analysis.

Conclusions : Intermittent light exposures of 5500 lux are over 2-fold more effective than equiluminous continuous exposures for preventing FDM and increasing scleral stiffness. Intermittent exposure to higher light levels may be more effective and practical for myopia prevention.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.

 

Fig 1. Illuminance-dependent impact of CL and IL on IODs in AL (A), refraction (B) and CT (C). D. Scleral stiffness in FD eyes exposed to 5500 lux of CL or IL, or no intervention (SL).