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Human Eye ( Part - 2 )


Hello, my friends I was talking about the accessory structure of the eye in the previous part. If you were not read the previous part of the human eye. Link ⇒ Human Eye ( Part - 1 )

Today I will talk about the internal structure of the eye.


#Internal Structure of the Eye --

1. Fibrous tunic -
- The outermost covering of the eyeball.
- Made of hard and thick connective tissue.
- Mesodermal in origin.
- Non-vascular in nature.
  This layer is divided into 2 parts: -

a. Cornea

- Outer visible part.
 - Covered by Non keratinized stratified squamous epithelium.
 - Lacks blood vessels ( cornea transplantation is successful for this reason ).

b. Sclerotic layer / Sclera

- Hard, opaque thick fibrous connective tissue in the human.
- It is the inner portion of the eyeball.
- Non-vascular in nature.
- White in nature ( Due to this reason it is also called white of the eye).

The Joint between the cornea and sclera is called Limbus or Sclera - corneal junction.


2. Vascular tunic

- The middle layer of the eye.
- The coloured part of the eye.
- Richly supplied with blood capillaries ( Highly vascularized ).
- It contains melanin pigment which is responsible for the colour of the eye ( brown, black, blue, green ) according to melanin present.

This layer has 3 types: -

a. Choroid layer

- Origin - mesodermal.
- It presents below the sclera.
- Contains abundant pigment cells and blood vessels.
- Look bluish in colour.
- It darkens a cavity of the eyeball to prevent internal reflection of light.
- It nourishes the retina.

b. Ciliary body

- Ectodermal in origin.
- The lower swollen portion below the limbus.
- It has ciliary processes which project into the eyeball.
- It has two ciliary muscles ( ciliary muscles help for changing the shape of the eye lens ).
i > Circular
ii > Meridional

c. Iris

- Ectodermal in origin.
- It is present from the vascular tunic that separates from the sclerotic layer inclines towards the inner side and forms a coloured screen.
- It presents an aperture in the centre of the iris, it is called the pupil.
- It acts like the diaphragm of a camera.

2 types of muscles related to the Iris --


a. Radial dilatory muscles

- It is the outer unstriated muscles.
- That is expanded in the iris breath wisely.
- If the contract and the diameter of the pupil are increased. it happens in dim light ( This phenomenon is called Mydriasis ).

b. Circular sphincter muscles

- Scatted in the inner part of the iris.
- If its contracts and the diameter of the pupil is decreased. it happens in bright light ( This phenomenon is called Miosis ).

3. Neurosensory tunic

- About it, I will talk in the next part.

The next part is coming soon...........

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