Maintains low levels of EIF2S1 phosphorylation in unstressed cells by promoting its dephosphorylation by PP1. Part of a complex containing PPP1R15B, PP1 and NCK1/2 (By similarity). Interacts with PP1. The disease is caused by variants affecting the gene represented in this entry. Defects in PPP1R15B has been found in a patient with isolated coloboma, a defect of the eye characterized by the absence of ocular structures due to abnormal morphogenesis of the optic cup and stalk, and the fusion of the fetal fissure (optic fissure). Isolated colobomas may be associated with an abnormally small eye (microphthalmia) or small cornea. The phosphatase activity of the PPP1R15B-PP1 complex toward EIF2S1 is specifically inhibited by Salubrinal, a drug that protects cells from endoplasmic reticulum stress. Belongs to the PPP1R15 family.