There is no data on how long vitamin A works for the eyes, and those who need it should take medication or get it from food as prescribed by their doctor. Moreover, it has no therapeutic effect on diseases of the eye other than those caused by vitamin A deficiency. Since vitamin A can induce and control the differentiation and growth of epithelial tissues, it can maintain the normal structure and function of epithelial tissues required, such as skin, conjunctiva, cornea, etc.. It is worth noting that there is no authoritative data to show how long vitamin A works for the eyes, and due to the individual’s physical condition, the degree of absorption of vitamin A and other differences, so the specific time can not be judged. Because vitamin A can be converted to retinol in the retina, and with the combination of retinal protein to form retinol, in order to maintain the body in low light vision. When the body is deficient in vitamin A, the synthesis of retinoid is blocked, which causes night blindness. Patients can improve their vision by supplementing with vitamin A, but vitamin A has no therapeutic effect on other diseases for the time being. It is recommended that those who have the need for medication to use vitamin A under the guidance of a doctor, and not to use the medication on their own to avoid causing adverse reactions.