The appearance of “sleepy eye” could be the maninfestation of a refractive error (myopia, hypermetropia or astigmatism) or another anomaly. The period of visual learning starts at birth and ends at the age of 8-9 approximately, so if there is a pathology, it's essential to get proper diagnosis and treatment at this stage, otherwise he could end up with amblyopia or “lazy eye”.  What we don’t learn to see in infancy cannot be restored later on in adult life, so we recommend that all children have a full eye examination at the age of 2-3.