Adaptive, light-dependent mechanisms in children may be a pathway through which time outdoors influences refractive error development. “There is a greater difference between the response to the red and blue stimuli in individuals with shorter axial lengths, and that relationship is only present in the summer months,” Marielle Blumenthaler, an optometry student at the Ohio State University, said Wednesday morning at the AAO Press Conference on behalf of her team. A potential explanation for this effect is increased summer light exposure causing more robust intrinsically photosensitive retinal ganglion cells (ipRGC)-dependent pupil responses.

Ms. Blumenthaler and her team recently evaluated whether the season in which testing occurs affects the relationship between axial length (refractive error) and pupil responses to red and blue stimuli in 50 children between the ages of eight and 17. They found that pupils tended to become smaller during blue stimulation than during red stimulation, and the difference in these pupil sizes varied significantly based on the season in which testing occurred. Although subjects with less myopic refractive error tended to have larger differences in pupil size between blue and red stimulation, the team notes that this effect did not reach statistical significance in either winter or summer.

The researchers concluded that an adaptive ipRGC-driven dopaminergic pathway may exist in which shorter eyes take advantage of greater light exposure to further inhibit the growth of the eye and reduce the risk of the onset of myopic refractive error. “There is either more dopamine release in the retina or more response to dopamine in the retina in non-myopic individuals,” said Ms. Blumenthaler.

Blumenthaler M, Hartwick AT, Mutti DO. The association between axial length and pupil responses to blue and red stimuli in children depends on season. Academy 2018 San Antonio.