In Biology, the action of focusing the human visual system, by direct adjustment of the focal length of the crystalline lens in the eyes.

Cilliary muscles relax or contract to change the shape of the flexible crystalline lens. When the muscles are relaxed, the lens will be thin, and an object at infinity will be focused on the retina. As the object comes closer, the muscles contract, making the lens thicker while keeping the object in focus on the retina.

The closest point on which the eye can focus is called the near point. The near point is about 7cm in front of the eye for a teenager and gets farther with age.

The compliance to or the disruption of habitual responses in the accommodation mechanism serves as one of the physiological cues for depth perception.

The phenomenon of accommodation is the main reason why a stereo pair is insufficient in recreating three-dimentional scenes.