Vision is a learned skill. Vision is the ability to get meaning and understanding from what is seen by the eyes.
Vision is a different process than sight.
Although the health of the eye and the surrounding tissue is important, vision takes place in the brain and is the sum total of our visual experience. There is usually some dysfunctioning within the visual system, frequently caused by stress. The muscular control the eyes necessary for reading is directed by the visual cortex of the brain and is a skill progressively self taught from infancy. One of the recorded body reactions to the stress response is to engage peripheral vision making reading and understanding extemely unlikely. We note that, in working with learners experiencing difficulties, a fair proportion exhibit poor eye control and teaming skills suggesting that their learning experience was incomplete when they started reading.