Accommodation (from Latin accomodatio - adaptation) is the ability of the human or animal eye to adapt to viewing objects located at different distances.
The mechanism of accommodation consists of changing the curvature of the lens - its convexity. This allows the eye to focus images both on and in front of the retina.
When a person looks into the distance, the lens has less curvature. When you shift your gaze to a close object, the ciliary muscle contracts. This leads to tension in the ciliary girdle and an increase in the convexity of the lens. Thus, the lens becomes more spherical and can focus the image of nearby objects on the retina.
The ability to accommodate decreases with age due to loss of elasticity of the lens. This leads to presbyopia (farsightedness).