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Letter to the editor: Bright light induces choroidal thickening in chickens.

We read with great interest the article by Lan et al., reporting that bright light induces choroidal thickening in chickens. In that article, possible mechanisms underlying the transient changes of choroidal thickness induced by bright light were discussed. It was noted that bright light could affect choroidal thickness through the increased permeability of choroidal capillaries or increased choroid blood flow. To explain how retinal signals reach the choroid, it was speculated that bright light might trigger the release of dopamine and nitric oxide. The latter diffuses across the retinal pigment epithelium (RPE) and induces choroidal thickening. However, this neurochemically mediated signal transduction remains to be fully understood. The explanation may become more complete if we consider data showing that the choroidal blood flow may be affected by local heat-induced vasodilation through neurochemical mediators. The heat might trigger chemical cascades, leading to the release of dopamine and nitric oxide and subsequently vasodilation and increased choroidal blood flow. Changes in the local temperature might result from absorption of light by the pigments of the RPE and the underlying choroid. Therefore, it seems that the local temperature of the RPE and the underlying choroid in eyes exposed to bright light is higher than that in eyes exposed to normal light. In conclusion, the bright light might increase the local temperature of the RPE and the underlying choroid. The resultant heat might trigger neurochemical cascades, leading to the increased choroidal blood flow and thickness and consequently the decreased rate of ocular elongation and myopia progression. Further studies are needed to determine the potential effects of bright light on choroidal temperature and the rate of myopia progression. Based on these concepts, more appropriate strategies can be developed that may be helpful for delaying or preventing myopia and decelerating its progression.