Effects of flickering light on refraction and axial changes in the C57BL/6 mouse

Abstract

Objective To investigate the effectiveness and feasibility of inducing myopia in mice with flickering light (FL) stimulation. Methods Experimental study. Forty-five C57BL/6 (B6)mice at age 28 days were randomly divided into 3 groups: control group, FL group and form deprivation (FD) group. Mice in the control group were raised under an illumination of 250 lx from 8 :00 am to 8:00 pm, and 0 lx from 8:00 pm to 8:00 am. For the FL group, the mice were raised under an illumination of a 50% duty cycle at 2 Hz for 6 weeks. During each flicker cycle, luminance varied between the maximum and minimum light levels of 250 lx and 1 lx from 8:00 am to 8:00 pm and 0 lx from 8:00 pm to 8 :00 am. Mter 6 weeks of FL, mice were raised under the same conditions as the control group for 2 weeks. Form deprivation was accomplished by covering the right eye of the mouse with a semitransparent hemispherical thin plastic shell for an eye diffuser.Mice in FD were raised under the same conditions as the control group. The refractive state and axial length (AL) of the right eye were measured with murine-specific eccentric infrared photorefraction and A-scan ultrasonography, respectively. The data were collected at pre-treatment and at the end of 2, 4, 6 and 8 weeks post-treatment. During the experiment, the eyes and action of all the mice were also observed. A one-way ANOVA was used to compare refraction and AL between groups. A paired t test was used to compare refraction and AL before and after flicker in FL group. An independent samples t test was used to compare refraction and AL between FL group and control group. Correlation between AL and time, refraction was analyzed with a Regression analysis. Results After 6 weeks of FL stimulation, refraction became more myopic compared to the control group [(-2.49+1.32)D versus (6.26±1.18)D, P＜0.01)], and their AL increased faster [(3.12±0.04)mm versus (3.08±0.02)mm], P＜0.01]. A positive correlation between refractive error and AL was found after treatment (r2=0.677, P＜0.01). The myopic shift decreased towards hyperopia after the removal of FL stimulation. After 6 weeks of FD, FD eyes were more myopic than FL eyes [(-6.42±2.21)D versus (-2.49±1.32)D, P＜0.05]. The AL of the FD eyes was longer than those of the FL eyes [(3.27±0.04)mm versus (3.12±0.04)mm, P＜0.05). However, some mice lost their eye diffusers, and in some mice lens opacities were found. Conclusion Myopia can be induced by FL stimulation in the B6 mouse. A myopic shift induced by FL is less than that by FD, but there are fewer side effects from FL, and FL is safer and easier to manipulate. Key words: Myopia; Flickering light; Refraction; Axial length; Animal model; Mouse