A 4-year-old child’s vision of 0.4 is lower than normal, which needs to be alerted, and the causes of delayed vision development should be investigated and corrected. Under normal circumstances, 4-year-old children’s visual acuity can reach 0.8, for the vision of only 0.4 is already a more serious situation, the need for timely medical perfect dilated optometry and other ancillary examinations, clear causes of delayed vision development, to be timely and effective correction or vision training to promote the normal development of vision. The 4-year-old child’s corrected visual acuity of only 0.4 needs to be taken seriously, if the cause is not found and corrected in a timely manner is likely to be amblyopia and other tricky situations, resulting in delayed visual development may be congenital development, endocrine abnormalities, etc., but also may be the refractive paradox, strabismus, anomalous cover, etc., which need to be promptly corrected by wearing lenses, surgery, or visual acuity training. It is recommended that 4-year-old children with a visual acuity of 0.4 or other conditions that do not reach normal, should promptly consult a doctor to improve the dilated pupil optometry and other ancillary examinations, to identify the cause of the disease and take targeted measures.