Combining Narrow-Band Red and Blue Ambient Light Causes Moderate Myopia in Tree Shrews

Abstract

Purpose : To examine the effects of ambient light containing both narrow-band red and narrow-band blue on emmetropization in juvenile tree shrews (diurnal mammals closely related to primates).

Methods : Seven tree shrews were raised in fluorescent colony lighting on a 14:10 h schedule until they began wavelength treatment at 24 days of visual experience (DVE). Arrays of both 636±10 nm (red) and 464±10 nm (blue) LEDs were placed atop the cage, providing illuminance on the cage floor of 400 (blue) and 500 (red) human lux. After 35 days in dual-band lighting, the animals recovered in colony lighting. Non-cycloplegic refractive state (autorefractor) and axial dimensions (optical biometer) were measured daily in the awake animals. This group was compared with a group of animals left in colony light (Gawne et al. 2017).

Results : The combined narrow-band red and blue lighting produced myopia that appeared to stabilize at ≈ −2 D and commensurate vitreous chamber elongation, compared to animals raised in regular colony lighting (Fig.1). When returned to colony lighting, refractions and vitreous chamber depth quickly recovered towards normal.

Conclusions : Ambient narrow-band red light alone causes hyperopia in tree shrews (Gawne et al. 2017). Ambient narrow-band blue light alone causes refractive state to become unstable (Gawne et al. 2018). We hypothesized that combining the red and blue would maintain normal emmetropization using longitudinal chromatic aberration (LCA) cues because relative image contrast would vary with refractive state at both short and long wavelengths. However, the result was a small myopia. The presence of two narrow bands of light at distinct wavelengths may not provide sufficient information for the emmetropization mechanism to use defocus or LCA cues to maintain age-appropriate emmetropia. These results emphasize the importance of wavelength cues in emmetropization and may suggest that a more continuous band of wavelengths is necessary for the emmetropization mechanism to function normally.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.

 

A: Refraction vs. age (mean±std err). B: Vitreous chamber depth vs. age. The mean during treatment was subtracted from each animal's data to factor out differences in eye size, and zero was set as the starting point. In normal animals the vitreous chamber shortens because the large tree shrew lens is growing. DVE = days of visual experience after normal eye opening at about 3 weeks of age.