Accommodation is the ability of the eye lens to change its curvature and optical strength, adapting to the viewing of objects at different distances. As a result of cooperation of lens and ciliary muscle of the eye, a clear image is formed. When child is looking into the distance, the ciliary muscle is relaxed and the Zinn’s zonules between the lens and the ciliary muscle pull eye lens towards the ciliary muscle. If, during the day, the child is doing activities close to eyes and foor a long time, for example, when reading or writing, then the ciliary muscle is in permanent contraction condition and is unable to relax that in turn causes eye fatigue in the evenings, and the child experiences difficulties of seeing small objects in the distance and in the vicinity. Spasms of accommodation may also cause headaches, light sensitivity may be increased.
The tension and relaxation of the ciliary muscle occurs all the time, and it does not depend on human will.