Accommodation (vertebrate eye)

Minimum (top) and maximum accommodation (bottom).
Two horse lenses suspended on water by cling wrap with four approximately parallel lasers directed through them. The 1 cm spaced grid indicates a near focus focal length of around 6 cm

Accommodation is the process by which the vertebrate eye changes optical power to maintain a clear image or focus on an object as its distance varies. In this, distances vary for individuals from the far point—the maximum distance from the eye for which a clear image of an object can be seen, to the near point—the minimum distance for a clear image. Accommodation usually acts like a reflex, including part of the accommodation-convergence reflex, but it can also be consciously controlled.

The main ways animals may change focus are:

  • Changing the shape of the lens.
  • Changing the position of the lens relative to the retina.
  • Changing the axial length of the eyeball.
  • Changing the shape of the cornea.