Difference Between Sclera and Conjunctiva

The key difference between sclera and conjunctiva is that the sclera is the thick white layer that makes the white part of the eye while the conjunctiva is the thin translucent layer that surrounds the entire eye except for the cornea.

Eyes are one of the vital organs in our body, which give our vision. In other words, we see everything around us due to this organ. Therefore, they detect light and convert into electrochemical signals that are read by our nervous system. As a result, we are able to see three dimensional, moving and coloured images. The eye consists of different components such as iris, cornea, pupil, sclera and conjunctiva.

CONTENTS

1. Overview and Key Difference
2. What is Sclera
3. What is Conjunctiva
4. Similarities Between Sclera and Conjunctiva
5. Side by Side Comparison – Sclera vs Conjunctiva in Tabular Form
6. Summary

What is Sclera?

Sclera is the white part of our eye, which is the dense connective tissue of the eyeball. Therefore, sclera accounts for more than 80% surface area of the eye, since it surrounds the cornea region as well.  Furthermore, it extends up to the optic nerve and exists in the back of the eye as well. The thickness of this tough outer coating ranges from 0.3 mm to 1.0 mm, which is made from fibrils of collagen. Furthermore, the random arrangement and interweaving of collagen fibrils in the sclera provide the strength and eyeball flexibility.

This layer is metabolically inactive. However, it helps the eyeball to maintain its shape. Moreover, it protects the eye from damages and toxic chemicals. It has relatively a limited blood supply. Moreover, the sclera is opaque, but it may turn into a yellowish colour during the disease called Jaundice while it turns into the black during kidney and liver failure. Scleritis is another serious disease condition that occurs due to inflammation of the sclera.

What is Conjunctiva?

The clear membrane covering the sclera and interior lining of eyelids is known as conjunctiva. It is a thin, transparent and vascularized mucous membrane. Conjunctiva does not cover the cornea of the eye. There are two main components of conjunctiva namely, bulbar and palpebral. The bulbar conjunctiva is a thin, semitransparent, colorless tissue that covers the sclera up to the corneoscleral junction. On the other hand, the palpebral conjunctiva is a thick and opaque red tissue.

Conjunctiva performs several important functions including protection of the soft tissues of the orbit and the eyelid, provision of the tear film’s aqueous and mucous layers, the supply of immune tissue and facilitation of independent globe movement, etc. Moreover, the inflammation of conjunctiva is known as conjunctivitis. Similarly, Conjunctivitis is the inflammation of the conjunctiva.

What are the Similarities Between Sclera and Conjunctiva?

• Sclera and Conjunctiva are two parts of the eye.
• Both are protective layers of the eye.
• Sclera and Conjunctiva are vascularized tissues.
• They perform important functions in the eye.

What is the Difference Between Sclera and Conjunctiva?

Sclera and conjunctiva are two important parts of the eye. Both are protective layers of the eye. Sclera is the white part of the eye that covers more than 80% of the eye including the cornea. Conjunctiva is the thin transparent layer that lies on the sclera and interior lining of eyelids. Conjunctiva is a highly vascularized tissue while sclera has a limited blood supply. The below infographic presents the difference between sclera and conjunctiva as a side by side comparison.

Summary – Sclera vs Conjunctiva

Sclera is also known as white of the eye is the dense connective tissue of the eyeball. It is an opaque protective layer that covers most of the eye areas. It extends up to the optic nerve as well. Conjunctiva is the clear membrane covering the sclera and interior lining of eyelids. This is the difference between sclera and conjunctiva.

Reference:

1.“Conjunctiva.” Egyptian Journal of Medical Human Genetics, Elsevier. Available here 

Image Courtesy:

1.”Sclera”By Mikael Häggström (CC0) via Commons Wikimedia  
2.”1411 Eye in The Orbit”By OpenStax College – Anatomy & Physiology, Connexions Web site, Jun 19, 2013., (CC BY 3.0) via Commons Wikimedia