A 9 year old child with 0.4 vision is below normal, but not necessarily due to myopia.
Normally, by the time a child reaches the age of 6, the child’s vision should be able to develop to 1.0, and a 9 year old child with 0.4 vision is below normal.
Since many ophthalmologic conditions can cause vision loss, it is not possible to simply attribute vision loss to myopia. In addition to myopia, astigmatism, hyperopia, amblyopia, cataracts, and fundus lesions may all manifest as poor vision.
A 9-year-old child with 0.4 visual acuity should be taken to the ophthalmology department of the hospital for timely examination: slit lamp microscopy, optometry, funduscopy, etc., to clarify the causes of vision loss, and then targeted treatment can be taken.