Blue Light Guides a Color Contrast Sensitive Emmetropization Response at High Temporal Frequency

Abstract

Purpose : Previous studies have examined the role of temporal sensitivity to luminance flicker and color flicker in the emmetropization response. We investigate how the sensitivity to color contrast at low (0.2Hz) and high (10Hz) temporal frequencies affects emmetropization.

Methods : Ten-day-old chicks were exposed to sinusoidal color modulation of short (S-) and longer (LM-) wavelength sensitive cones producing blue/yellow (BY) flicker (n=57), or long (L-) and middle (M-) wavelength sensitive cones producing red/green (RG) flicker (n=74), at 10, 20, 30, 40, 60, and 80% contrasts. One condition of red/green flicker at 40% contrast did not employ double cone stimulation (n=14). Exposure duration was between the hours of 9am and 5pm over a 3-day period. Low and high modulation frequencies were used. Mean illumination was 680 lux. Changes in ocular components and refractive error were measured using Lenstar and a Hartinger refractometer.

Results : Vitreous chamber depth was dependent upon temporal frequency and contrast (P=0.006) and color and contrast (P=0.01). At a high temporal frequency, blue/yellow color contrast produced an increase in the mean change in vitreous chamber depth with increasing contrast (R²=0.267, P=0.003). The increase in vitreous chamber depth was accounted for by a decrease in lens thickness (R²=0.056, P=0.032). At a low temporal frequency, red/green color modulation with 40% contrast minimized the mean change in vitreous chamber depth (0.14 ± 0.02mm), indicating a threshold effect. This all-or-nothing response was enhanced by double cone stimulation (P=0.0001). The decrease in vitreous chamber depth was accounted for by an increase in choroid thickness, which was maximized (0.03 ± 0.01mm) in the red/green group at 40% contrast. These maximum/minimum values differed statistically (P<0.0001). Compared to historical luminance contrast data, discordant trends in vitreous chamber depth and choroidal thickness were observed.

Conclusions : At a high temporal frequency, the graded response to blue/yellow color contrast provides a reliable growth signal for emmetropization. At a low temporal frequency, the threshold response to red/green color contrast promotes choroidal thickening, which is enhanced by double cone stimulation. These findings confirm the results of previous studies reporting that blue light is important in emmetropization.

This is a 2020 ARVO Annual Meeting abstract.

 

Mean change/standard error for vitreous chamber depth.