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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...........

Which part of this blog do you like most. Give us your point of view in the comment section and let us know what you think, don't forget to follow this blog and share it with your friends. Stay with the Aryan Ideas.
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