Difference Between Conjunctiva and Sclera (With Table)

The human eye is a wonderful tool. We can see this beautiful world in 576 megapixels, all because of our eyes. It is one of the most important organs of our whole body. The eye is made up of many parts, which together make it possible for us to see and to be able to protect our eyes from external harm.

Two of these parts of the eye are known as conjunctiva and sclera.

Conjunctiva vs Sclera

The difference between conjunctiva and sclera is that the conjunctiva helps in lubricating the eye by providing mucus and tears and also helps prevent microbes from entering the eye, whereas sclera helps in protection of the interior parts of the eye and also in identifying patients who have jaundice (the sclera turns yellow when one has jaundice).

Comparison Table Between Conjunctiva and Sclera

Parameter of ComparisonConjunctiva Sclera
LocationThe conjunctiva covers part of the front surface of the eye and also covers the inner surface of the eyelids.The sclera begins at the limbus, another part of the eye and it terminates at the optic nerve canal posteriorly. 
FunctionThe conjunctiva is a thin membrane.

It helps in keeping the eye lubricated and also contributes to the tears and the tear lining. 
It also helps in keeping the innermost surface of the eyelids lubricated so that the eyelid opens and closes without irritation.

It helps protect the eye from foreign particles and microbes and thus helps in preventing damage to the eyes.
The sclera is a thick membrane.


It provides protection to the eye.

Sclera also helps in maintaining the shape of the globe and thus helps in maintaining the form of the eye.
Thickness0.013 mm0.5 mm
Own blood vesselsYesYes
Own nerve supplyYesYes

What is Conjunctiva?

The conjunctiva is known as the mucous membrane of the eye. The conjunctiva is made up of stratified columnar epithelium, and nonkeratinized, stratified squamous epithelium with goblet cells. It is divided into 3 parts, Palpebral or tarsal conjunctiva, Bulbar or ocular conjunctiva, and Fornix conjunctiva

There is a direct supply of blood to the conjunctiva. The blood supply is through the ophthalmic artery and the external carotid artery. It also has its own nerve supply and the sensory information is divided into superior, inferior, lateral, and circumcorneal.

The role of the conjunctiva is to lubricate the eye. It produces mucus and tears and hence keeps the eye lubricated. It also helps in immune surveillance of the eye and helps in the prevention of entering of microbes into the eye. 

A common disease that affects the conjunctiva is known as conjunctivitis which is redness and swelling of the eye. This disease is caused by the irritation of the conjunctiva. The conjunctiva responds by reddening and swelling itself.


What is Sclera?

The white part of the eye, the part that you can see, is known as the sclera. The sclera is made up of collagen and elastic fiber. The sclera has 4 layers. The very inside layer is known as the endothelium, the next layer is called stroma, the next is called lamina fusca. The very last and outer layer is known as the episclera.

There is a direct supply of blood to the sclera. It receives its supply through the anterior ciliary arteries, long posterior ciliary arteries, and short posterior ciliary arteries. It also has its own nerve supply and is supplied by the long ciliary nerves anteriorly and short ciliary nerves behind the equator.

The sclera is made up of fibers and therefore is tough and fibrous. The function of the sclera is to protect the interior parts of the eye (retina, blood vessels, nerve vessels, and lens) from outside damage. Another function of the sclera is supporting the wall of the eye, i.e it helps in maintaining the shape of the eye.

The sclera also makes up for the exterior coating of the eye. The visible white portion of the eye that you see is because of the sclera.

A common disease of the sclera is scleritis, in which the sclera becomes severely inflamed and turns red. If scleritis isn’t treated, it can even lead to vision loss.

Main Differences Between Conjunctiva and Sclera

  1. The conjunctiva is a thin membrane. On the other hand, the sclera is a relatively thick membrane.
  2. The conjunctiva has 3 parts, namely tarsal conjunctiva, ocular conjunctiva, and Fornix conjunctiva. On the other hand, the sclera is divided into 4 parts, namely endothelium, stroma, lamina fusca. and episclera.
  3. The main function of the conjunctiva is to provide protection from microbes and foreign particles entering the eye, to lubricate the eyes, to contribute to the tear lining, and help ease the movement of the eye and the eyelids. On the other hand, the main function of the sclera is to provide a form or shape to the globe of the eye, supporting the wall of the eye and protecting the internal parts of the eye (retina, blood vessels, nerve vessels, and lens) from outside harm. 
  4. The size of conjunctiva varies but the mean is found to be around 0.013 mm. On the other hand, the size of the sclera also varies, but the mean is found to be around 0.5 mm.
  5.  The conjunctiva is made up of stratified columnar epithelium, and nonkeratinized, stratified squamous epithelium with goblet cells. On the other hand, the sclera is made up of collagen and elastic fiber.

Conclusion

Conjunctiva is a thin membrane that covers the front and back of the eyelids whereas sclera is a relatively thick membrane. Both these parts of the eye have their own blood and nerve supply. Both of these parts of the eye perform important functions for the eye and are essential for the eye to function correctly and effectively.

References

  1. https://www.sciencedirect.com/science/article/pii/B9781483230900500137
  2. https://bjo.bmj.com/content/80/11/994.short
  3. https://onlinelibrary.wiley.com/doi/abs/10.1046/j.1475-1313.2000.00526.x
  4. https://iovs.arvojournals.org/article.aspx?articleid=2124109
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