The 12-year-old child’s naked eye visual acuity of 4.9 is slightly lower than normal, but it is not obvious abnormality, you need to check and clarify what causes, if it is caused by refractive error, you can wear glasses to correct, if it is caused by visual fatigue, you need to pay attention to rest to relieve. Under normal circumstances, children over the age of 6 should develop a visual acuity of 5.0, the current 12-year-old child’s visual acuity is only 4.9, which is slightly lower than normal, you need to go to the ophthalmology department of the hospital to find out the causes of vision loss, and for the cause of the treatment, but it can not be pathologic. The most common cause of vision loss is refractive error, which is related to congenital developmental abnormalities and poor eye habits, etc. It can be diagnosed through an optometry examination, and the child can wear glasses to correct nearsightedness and improve his/her vision. Visual fatigue caused by prolonged close eye use can also lead to vision loss, and children need to rest their eyes and avoid excessive eye use in order to improve their vision. Children with vision loss are advised to seek prompt medical attention to assess their condition and follow the doctor’s instructions.