Accommodation is the process where by a change in the curvature and thickness of the lens is adjusted in order to allow for the focusing of objects at different distances. As mention earlier in Anatomy and function of the Human eye and Refractive media, the lens is a transparent biconcave disc whose primary function is to refract light. The curvature and thickness of the lens determines the amount of refraction that occurs and this is controlled by the Ciliary bodies attached to the lens. When the Ciliary bodies relaxes the lens becomes thinner and has less curvature causing less refraction to occur and when the Ciliary bodies contracts the lens become thicker with more curvature where more refraction occurs.
When viewing a distant object, greater then 6 meters, light rays travel almost parallel and for this reason not much refraction need to occur in order to focus the light on the retina. When viewing a closer object, less then 6 meters, light travels to the eye at large angles causing a greater need for refraction to occur so the light can be focused on the retina. Therefore when viewing a distant object the Ciliary bodies relaxes in order to make the lens thinner and have less curvature so less refraction occurs and when viewing a closer object the Ciliary bodies contracts to make the lens thicker with more curvature to allow for more refraction to occur.
From this it is evident that accommodation is vital as it allows for light from different distances to be focused onto the retina for clear and sharp vision. Without accommodation light for different distances would become blurry humans would not have sharp sight for almost all distances.



http://www.youtube.com/watch?v=15P8q35vNHw&feature=related is the video above which represent the process of the lens as accommodation occurs and explains the process involved in accommodation.


Aubusson, Eileen Kennedy Peter. Biology in Context: the Spectrum of Life. Victoria : Oxford Uni. Press., 2001. Print.
"HSC Online." NSW HSC Online. N.p., n.d. Web. 20 June 2010. <http://www.hsc.csu.edu.au/biology/options/communication/2951/CommPart3.html#a1>.