Children’s eyes, and many adult’s eyes, often turn in when reading because they are farsighted or hyperopic.
When eyes are hyperopic, focusing on near objects, also known as accommodation, causes the eyes to converge or turn in. Hyperopes who don’t wear their glasses must focus their eyes, or accommodate, to a large degree in order to see clearly at near.
These focusing attempts stimulate the accommodative reflex which in turn causes the eyes to converge. When the convergence of the eyes is greater than the amount the eyes can focus, the eyes then will turn in even more making the eyes appear crossed. This is called accommodative esotropia.
This is easily corrected by wearing and eyeglass or contact lens prescription with plus lenses of suitable strength. With the patient wearing the correct prescription, the eyes will not be turning in anymore.