DDIT3 and retinal degeneration: Tubacin, an HDAC6 inhibitor, restores prx2 expression, which is a retinal antioxidant, and reduces retinal degeneration.134 Valproate, a bipolar disorder and epilepsy drug, can inhibit HDAC as well and is proven to increase the expression of BiP and decrease CHOP, which disturbs harmful ER stress and protects RGCs.136 Drugs targeting ER stress and autophagy to rescue RGCs with OPTN mutations have been studied.