The effect of monochromatic light on eye growth of chicks with competing optical defocus

Abstract

Purpose : To examine the effects of monochromatic lights on chicks wearing dual power optical lenses

Methods : Four groups of white Leghorn chicks aged 5 days (n = 8 per group) were kept in a cabinet (80 x 80 x 125 cm) in four different monochromatic lighting; white (588 nm), red (631 nm), green (524 nm) and blue (451 nm). The average illuminances in all environments were around 250 lux. After the baseline measurement of ocular parameters and refractive errors, one eye was fitted with dual power optical lens (-10D/+10D, 50:50) while another eye was left untreated as control. Chicks were then kept in one of these 4 lighting conditions for 13 days. Ocular parameters and refractive errors were measured after 13 days. Changes in the ocular parameters and refractive errors relative to the baseline were compared using two-way ANOVA and Fisher’s least significant difference (LSD) post hoc test.

Results : After 13 days of lens wear, shorter vitreous chamber depth (VCD) was observed in chicks exposed to white, green or blue light compared to the contralateral control eyes (p < 0.05 in three lighting conditions).
The growth in the VCD in control eyes was significantly slower under blue and green light when compared to those reared in white light. In eyes with dual power lenses, the eye growth in the VCD under blue and green light were significantly slower than those reared in white light condition (mean change in VCD ± SEM; white vs. red vs. green vs. blue; 0.54 ± 0.08 mm vs. 0.52 ± 0.10 mm vs. 0.29 ± 0.06 mm vs. 0.27 ± 0.07 mm; p < 0.05 in white vs. blue and white vs. green).
Similar magnitude of axial eye growth was found between lens wearing eyes and control eyes under red conditions. Moreover, refractive errors remained hyperopic after 13 days of exposure in the chicks wearing dual power lenses in all conditions (white vs. red vs. green vs. blue; 4.81 ± 0.42 D vs. 2.44 ± 1.19 D vs. 4.56 ± 0.61 D vs. 6.36 ± 0.39 D; mean± SEM).

Conclusions : Monochromatic lighting is known to affect eye growth in chicks without lenses. Competing defocus (with -10/+10 lens) resulted in shorter VCD and axial length under white light. In addition, when exposing to same competing defocus under blue and green lighting conditions, the eye growth in chicks was further retarded. The additive effect suggests that spectrum composition of lighting may be an important environmental variable for modulating eye growth and controlling human myopia.

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