Posted by jayaram in The lens of the eyeball is crystalline in nature. It is biconvex, transparent and possesses the elastic property. The lens does not have blood supply and receives its nutrition mainly from the aqueous humor. The focal length of human lens is 44mm and its refractory power is 230.
STRUCTURE OF THE LENS
The lens is formed of three components
The Capsule
Capsule is a highly elastic membrane covering the lens.
The Anterior Epithelium
It is a single layer of cuboidal epithelial cells situated beneath the capsule. At the margins, the epithelial cells are elongated. The epithelial cells give rise to the lens fibers present in the lens substance
The Lens Substance
This is formed by long lens fibers derived from the anterior epithelium. The lens fibers are prismatic in nature and are arranged in concentric layers.
CHANGE IN THE LENS DURING OLD AGE
After 40 to 45 years, the lens loses its elastic property. Because of this, the amplitude of accommodation is decreased. So, the person cannot see the near objects clearly. This condition is known as presbyopia. In old age after 55 to 60 years, the lens becomes opaque due to the accumulation of fluid and denaturation of the proteins of the lens fibers. This condition is called cataract.
PRESBYOPIA
In old age, the amplitude of accommodation is reduced as the near point is away from the eye. This condition is called presbyopia.