We subsequently examined the protective effect of DMF against BL exposure on ARPE-19 cells in vitro. ARPE-19 cells were exposed to culture solution with DMF for 3 h, cultured under BL for 24 h, and the LDH activity, cell viability, and amount of ROS were determined. BL exposure induced ARPE-19 cells to release LDH, which DMF reduced. LDH was 30.9 ± 1.2% (n = 4), 25.0 ± 2.4% (n = 4), and 19.1 ± 3.6% (n = 4) with 0, 10, and 100 μM DMF, respectively, displaying a dose-dependent effect (0 μM vs. 10 μM and 10 μM vs. 100 μM; p = 0.0094 and 0.037, respectively) (Figure 2). By contrast, without BL exposure, the LDH released was 14.2 ± 3.2% (n = 4), 13.2 ± 2.0% (n = 4), and 13.2 ± 2.8% (n = 4) with 0, 10, and 100 μM DMF, respectively, at 24 h, without any dose-dependent effect by DMF treatment (0 μM vs. 10 μM and 10 μM vs. 100 μM; p = 1.0 and 0.96, respectively) (Figure 2). The cell viabilities were 49.3 ± 10.5% (n = 4), 48.8 ± 13.9% (n = 4), and 60.1 ± 6.9% (n = 4) with 0, 10, and 100 μM DMF, respectively, at 24 h after BL exposure, this not being concentration dependent (0 μM vs. 10 μM and 10 μM vs. 100 μM; p = 1.00 and 0.54, respectively). By contrast, the BL-free/cell viabilities were 100.6 ± 10.7% (n = 4), 110.2 ± 6.6% (n = 4), and 107.8 ± 3.7% (n = 4) with 0, 10, and 100 μM DMF, respectively at 24 h, which were not significantly different from each other (0 μM vs. 10 μM and 10 μM vs. 100 μM; p = 0.69 and 1.0, respectively) (Figure 2). The fold-changes in ROS generation were 5.4 ± 1.2 (n = 6), 4.0 ± 1.9 (n = 6), and 2.0 ± 0.3 (n = 6) with 0, 10, and 100 μM DMF, respectively at 24 h after BL exposure, being significantly decreased at the higher DMF concentration (0 μM vs. 10 μM and 10 μM vs. 100 μM; p = 0.91 and n = 6), 1.1 ± 0.7 (n = 6), and 0.9 ± 0.5 (n = 6) with 0, 10, and 100 μM DMF, respectively at 24 h, showing no significant effect of DMF treatment (0 μM vs. 10 μM and 10 μM vs. 100 μM; p = 1.0 and 1.0, respectively) (Figure 2).