High Quality Content by WIKIPEDIA articles! Accommodation is the process by which the vertebrate eye changes optical power to maintain a clear image (focus) on an object as its distance changes. Accommodation acts like a reflex, but can also be consciously controlled. Mammals, birds and reptiles vary the optical power by changing the form of the elastic lens using the ciliary body (in humans up to 15 diopters). Fish and amphibians vary the power by changing the distance between a rigid lens and the retina with muscles. The young human eye can change focus from distance to 7 cm from the eye in 350 milliseconds. This dramatic change in focal power of the eye of approximately 12 diopters (a diopter is 1 divided by the focal length in meters) occurs as a consequence of a reduction in zonular tension induced by ciliary muscle contraction. The amplitude of accommodation declines with age. By the fifth decade of life the accommodative amplitude has declined so the near point of the eye is more remote than the reading distance. When this occurs the patient is presbyopic.

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