Notably, miR-21 has been previously documented mainly as a negative regulator of retinal health, such as inhibition of neovascularization in the ischemic retina by targeting tissue inhibitor of metalloproteinase 3 [61], induction of Müller cell gliosis after optic nerve crush by regulating glial fibrillary acidic protein [39], promotion of autoimmune uveoretinitis by targeting interleukin-10 [62], and facilitation of the progression of retinoblastoma by targeting phosphatase and tensin homolog [63]. Here, TIMP3 is linked to retinoblastoma.