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The lens, or crystalline lens, is a transparent biconvex structure in most land vertebrate eyes.Relatively long, thin fiber cells make up the majority of the lens. These cells vary in architecture and are arranged in concentric layers.
The α-crystallin family and βγ-crystallins compose the major family of proteins present in the crystalline lens. They occur in all vertebrate classes (though gamma-crystallins are low or absent in avian lenses); and delta-crystallin is found exclusively in reptiles and birds. [13] [14]
The lens is suspended to the ciliary body by the suspensory ligament (zonule of Zinn), made up of hundreds of fine transparent fibers which transmit muscular forces to change the shape of the lens for accommodation (focusing). The vitreous body is a clear substance composed of water and proteins, which give it a jelly-like and sticky composition.
The zonule of Zinn (/ ˈ t s ɪ n /) (Zinn's membrane, ciliary zonule) (after Johann Gottfried Zinn) is a ring of fibrous strands forming a zonule (little band) that connects the ciliary body with the crystalline lens of the eye. [1] The Zonular fibers a viscoelastic cables, although their component microfibrils are stiff structures.
The eye's natural lens is usually replaced with an artificial intraocular lens (IOL) implant. [2] Over time, metabolic changes of the crystalline lens fibres lead to the development of a cataract, causing impairment or loss of vision. Some infants are born with congenital cataracts, and environmental factors may lead to cataract formation.
Intraocular lenses have been used since 1999 for correcting larger errors in near-sighted, far-sighted, and astigmatic eyes. This type of IOL is also called phakic intraocular lens (PIOL), as it is implanted without removing the patient's natural crystalline lens.
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The lens front can then reform its shape between the suspensory ligaments in a similar way to a slack chain hanging between two poles might change its curve when the poles are moved closer together. This model requires precise fluid movement of the lens front only rather than trying to change the shape of the lens as a whole.