The lens capsule is a component of the globe of the

eye Eyes are organs of the visual system. They provide living organisms with vision, the ability to receive and process visual detail, as well as enabling several photo response functions that are independent of vision. Eyes detect light and conv ...

. It is a clear, membrane-like structure composed of collagen IV and laminin that is quite elastic, a quality that keeps it under constant tension. As a result, the lens naturally tends towards a rounder or more globular configuration, a shape it must assume for the eye to focus at a near distance. Lens capsule is the thickest basement membrane in the body. Normally, the lens capsule serves as a diffusion barrier. It is permeable to low molecular weight compounds but restricts the movement of large colloidal particles.

Anatomy

The lens capsule is a transparent membrane that surrounds the entire lens. The capsule is thinnest at the posterior pole with approximate thickness of 3.5μm. Average thickness at the equator is 7μm. Anterior pole thickness increases with age from 11-15μm. The thickest portion of is annular region surrounding the anterior pole. This will also increases with age (from 13.5-16μm). Even though the capsule is a highly elastic structure, it contains no elastic fibers. Elasticity is because of the thick lamellar arrangement of the collagen fibers.

Embryology

The lens vesicle is developed from surface ectoderm. It will separate from surface ectoderm at approximately day 33. Lens capsule developed from basal lamina of lens vesicle will cover early lens fibers. Capsule is evident at 5 weeks of gestation.

Vascular lens capsule

During fetal development vascular lens capsule (tunica vasculosa lentis) develop from the

mesenchyme Mesenchyme () is a type of loosely organized animal embryonic connective tissue of undifferentiated cells that give rise to most tissues, such as skin, blood or bone. The interactions between mesenchyme and epithelium help to form nearly every o ...

that surrounds the lens. It receives arterial blood supply from the hyaloid artery. This blood supply slowly regress and vascular capsule disappear before birth. The disappearance of the anterior vascular capsule of the lens is useful in estimating the gestational age.

Function

The capsule helps give the lens its spherical shape.

Accommodation

Normally, when ciliary muscles are in relaxed state, the

zonules The zonule of Zinn () (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. These fibers are sometimes colle ...

will pull the capsule. Due to this zonular tension anterior lens surface becomes flat. When ciliary muscles contract, this zonular tension will reduce allowing lens to assume more spherical shape. This shape change increase the whole power of the eye, and people will be able to see near clearly. The process of changing lens power to see near clearly is known as accommodation.

Lens protection

Early embryologic development of lens capsule give lens materiel an immune privilege. It will also help protecting lens from virus and bacteria.

Clinical significance

In intra-capsular cataract extraction (ICCE), whole lens including capsule is removed. During more common extra capsular cataract surgery procedures like micro inscision cataract surgery, phacoemulsification etc., clouded lens is removed through opening made in anterior lens capsule. The intraocular lens is then inserted into the lens capsule. The best place for intraocular lens implantation is within the capsular bag.

Posterior capsular opacification Cataract surgery, also called lens replacement surgery, is the removal of the natural lens of the eye (also called "crystalline lens") that has developed an opacification, which is referred to as a cataract, and its replacement with an intraocu ...

and posterior capsule rupture are common complications of cataract surgery.

References

{{DEFAULTSORT:Capsule Of Lens Human eye anatomy