Measurements of outer nuclear layer (ONL) thickness following 670-nm light treatment and bright continuous white light (BCL) exposure. The thickness of the ONL decreased significantly following exposure to BCL, compared to both dim-reared and dim-reared + 670 nm groups (P <0.05). In comparison, the ONL was significantly thicker in animals treated with 670-nm light prior to BCL exposure (P <0.05). Dim reared n = 3, dim reared + 670 nm n = 3, light damage n = 3, light damage + 670-nm light n = 3; error bars represent SEM. *Significant change using analysis of variance (ANOVA) with Tukey’s post test where P <0.05.