Middle layer of the eyeball:-Tunica media or Tunica vasculosa:

This article is based on the middle layer of the eyeball.

Q. Describe the middle layer of the wall of the eye?

Q.Middle layer of the eyeball is called,

Wall of the eyeball consists of three layers:

A:Outer layer ,

B: Middle layer,

C: Inner layer,

Middle layer of the wall of the eye:

Middle layer of the eyeball is also known as Tunica media or Tunica vasculosa.This layer surrounds the eyeball completely, except for a small opening in front known as pupil.

Different parts of the middle layer of eyeball

Middle layer of the eyeball consists of three structures:Choroid, Ciliary body, Iris.

1.Choroid:

Choroid is present in-between sclera and retina. This is a thin vascular layer of the eyeball.Up to the insertion of ciliary muscle,this vascular structure of the eyeball is extended anteriorly.

With the help of the perichoroidal space, choroid is separated from sclera (Tough white fibrous outer layer of the eyeball). Anteriorly this space is limited by the insertion of ciliary muscle into sclera.

Posteriorly this space ends at a short distance from the optic nerve.Inner surface of choroid joins with the first layer of the retina , that is the layer of pigment epithelium.

This structure of the middle layer of the eyeball is consists of numerous small arteries, capillary plexus,and veins.

2.Ciliary body:

Ciliary body of the middle layer of the eyeball is present in between choroid and iris.Ciliary body is the thickened anterior part of the middle layer of the eye. In front of the ora serrata it is situated.

Basically it is a ring shaped structure.With the help of the perichoroidal space outer surface of the ciliary body is separated from sclera.

Inner surface of the ciliary body of the middle layer of the eyeball faces the vitreous body and lens(crystalline structure of the eyeball).

From the lens of the eyeball a special structure namely suspensory ligaments arises,which then joins with the ciliary body.

Anterior surface of ciliary body of the middle layer of the eye faces towards the center of cornea. From the surface the iris arises.

There is present the parts in the ciliary body of the human eye, these are : Orbiculus ciliaris,ciliary body proper, ciliary processes.

a . Orbiculus ciliaris:

This structure is continuous with the choroid. Posterior two third of the ciliary body is made up of orbiculus ciliaris. Orbiculus ciliaris is 4 mm broad.

b.Ciliary body proper:

Outer longitudinal muscle and inner longitudinal muscle is involved in the formation of the ciliary body proper.

c.Ciliary processes:

From the inner surface of the ciliary body one type of finger like projections arises,which are known as ciliary processes.

There is present approximately 70 ciliary processes projecting towards the central axis of the eye to form radial fringes called corona ciliaris.

Iris:

Iris is situated in front of the lens. This is a thin curtain like structure of the eyeball of the eye. Iris forms a thin circular diaphragm with a circular opening in the center called pupil.

Iris,Pupil etc.

Iris is formed by two types of muscles: Pupillary constrictor muscle and pupillary dilator muscle .

Pupillary constrictor muscle:

Pupillary constrictor muscle is also known as constrictor pupillae or iris sphincter muscle. Pupillary constrictor muscle is formed by circular muscle fibres.

If the pupillary constrictor muscle contract,it can cause the contraction of the pupil.

Pupillary dilator muscle:

Pupillary dilator muscle is formed by radial muscle fibers. If the pupillary dilator muscle contract it can cause the dilation of the pupil.

Activities of the pupillary constrictor muscles and pupillary dilator muscles increase or decrease the diameter of the pupil and there by regulate the amount of light entering the eye.

Thus iris acts like the diaphragm of a camera.

Iris separates the space between cornea and lens into two chambers,which are known as anterior and posterior chambers.

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