Required for the localization of ZFYVE1 to lipid droplets and for its function in mediating the formation of endoplasmic reticulum-lipid droplets (ER-LD) contacts (By similarity). Plays a role in apical endocytosis/recycling (By similarity). Plays a key role in eye and brain development and neurodegeneration (PubMed:21473985). The most common abnormalities observed at 3 days post-fertilization are microphthalmia, microcephaly, pericardial edema, delayed jaw formation, a reduced overall body size, and a general developmental delay. Further characterization revealed that the rab18b morphants have delayed retinal development and abnormal retinal lamination, residual nucleated lens fiber cells, widely open choroid fissure, and microphthalmia at day 3. Belongs to the small GTPase superfamily. Rab family.