Background Presbyopia is a physiological condition arising due to the loss of accommodation within the crystalline lens. One of the most widely accepted theories of the mechanism of accommodation was that in response to ciliary muscle contraction, the crystalline lens thickness increases, the lens diameter decreases, and both the anterior and posterior curvature of the lens increase, resulting in an increase in lenticular power therefore, accommodation. A contrasting theory suggests that ciliary muscle contraction leads to a selective increase in equatorial zonular tension, with the lens equator moving toward the sclera and the equatorial diameter of the lens increasing.
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