To change our focus from distance viewing to near for reading, our brain must interpret how far away the object in space is located and then send a signal to the ciliary muscle inside our eye causing it to change the shape of the crystalline lens to exactly focus for that distance.
Our focusing ability is greatest in childhood and progressively declines throughout most of our life until after age forty, the focus has declined to require reading lenses or bifocals. Trauma to the brain may reduce the ability to focus accurately in young people and may lead to the need for reading correction or bifocals. Spasms of accommodation may occur causing over focusing and may present as a temporary increase in myopia.
Post Trauma Vision Syndrome may impair our ability to interpret spatial relationships and accurately coordinate the focus and convergence mechanism.