Presbyopia & accomidation
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ACCOMMODATION
(the ability of the eye to focus at various distances)
The normal lens inside the human eye has the ability to change shape, and hence its power. This allows it to focus light on the retina whether the light is coming from far away (the lens becomes thin), or from a near object (the lens becomes thick)
illustration from Answers.com
To focus on a near object, like when reading a book or seeing something closely, the lens inside the eye increases its curvature, so that the power of the eye is increased and the image comes to a good focus on the retina or the sensitive film in the back of our eyes. This process is called accommodation, and is strongest in early life.
However, the lens’s ability to accommodate declines with time because of a natural loss of its elasticity. Presbyopia is the result of these changes and is noticed when we reach our 40’s and 50’s. This is why reading glasses become necessary – they provide the extra focusing power required to see near.
In recent years, we started to have several options for correcting this focusing difficulty by laser treatment or by the implantation of a multifocal lenses inside the eye after removing the naturally occurring lens. This is an excellent alternative for people who have cataract and need it to be removed. After removing the opaque lens (cataract), we now have the option of implanting an artificial multifocal lens (several excellent options are available in recent years), and thus restoring the ability of focusing the eye on far, intermediate and near objects.