Average measurements of adult lens

  • Thickness = 4-5 mm
  • Diameter = 10 mm
  • Radius of curvature of the anterior surface = 10 mm
  • Radius of curvature of the posterior surface = 6 mm
  • Dioptric power = 17 D
  • Refractive index for Cortex = 1.386 & Nucleus = 1.406


  • The lens is a biconvex, transparent structure located immediately in front of the vitreous body and behind the iris.
  • The center points on its anterior and posterior surfaces are referred to as the anterior and posterior poles, respectively. A line joining these two poles forms the axis of the lens.
  • The marginal circumference of the lens is called the equator.
  • Male lenses are heavier than female lenses.

The lens is made up of 3 parts

  1. Lens capsule
  2. Lens epithelium
  3. Lens fibres

Lens capsule

  • It is a transparent acellular elastic basement membrane that grows in size to accommodate the ever-enlarging lens.
  • It is thickest on the anterior and posterior surfaces close to the equator (20 microns) and thinnest at the posterior pole (3 microns).
  • The thick basement membrane is formed by the lens epithelium anteriorly and by superficial lens fibres posteriorly.
  • By light microscopy the capsule appears homogeneous, but electron microscopy reveals a fibrillar structure with a more dense outer layer (the zonular lamella) into which the zonules penetrate.
  • The lens capsule is basically composed of type IV collagen combined with about 10% glycosaminoglycan.

Lens epithelium

  • Lens epithelium is a single layer of cuboidal cells that lie immediately beneath the anterior and equatorial region of the lens capsule.
  • At the equator, these cells elongate and form columnar cells, which become arranged in meridional rows. It is at the equator that lens epithelial cells become transformed into lens fibres.
  • At the equator, lens mitotic activity is at a maximum.

Lens fibres

  • Lens fibrres consitute the main mass of the lens. The fibres are formed by multiplication and differentiation of the lens epithelial cells at the equator. .
  • Each elongated lens cell is called a fiber. It is hexagonal in cross section and very long measuring abt 10 nm.
  • As each lens fiber moves to the interior of the lens, they lose their organelle.
  • As the lens increases in size, the lens fibres are unable to stretch the anteroposterior distance so that progressively more complicated suture patterns are formed.
  • Embryonic nucleus: the earliest fibre mass in the center of the lens – first 3 months of gestation.
  • Fetal nucleus: formed later with its Y-shaped sutures. – 3 to 8 months of gestation.
  • Adult nucleus: is composed of fibres formed after birth.
Suspension of the lens
  • The lens is held in position by a series of delicate radially arranged fibres collectively known as the suspensory ligament of lens or zonule.
  • The zonlues arise from the epithelium of the ciliary processes and are attached into the outer prt of the lens capsule near the equator of lens.


  1. Accommodation and presbyopia: When viewing near objects, the ciliary muscle contracts and the meridional fibres pull the choroid and ciliary body forward and the circular fibres; acting as a sphincter move the ciliary body inward, the zonules relax and the elastic lens assumes a more globular shape.

BUT with advancing age, the lens becomes less elastic, leading to so decreased accommodation, which causes presbyopia.

2. Cataract – senile, congenital, DM, trauma, complicated etc..

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