What is the Difference Between Sclera and Conjunctiva?

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The sclera and conjunctiva are two essential components of the eye that serve protective functions. The main differences between them are:

  1. Thickness and composition: The sclera is a thick, dense connective tissue that forms the white of the eye, while the conjunctiva is a thin, translucent membrane that covers the sclera and the inner lining of the eyelids.
  2. Vascularization: The conjunctiva is highly vascularized, containing many microvessels, whereas the sclera has a limited blood supply.
  3. Function: The sclera provides the eyeball with structural strength and protects against penetration and infection. The conjunctiva, on the other hand, helps protect the eye by keeping small foreign objects and infection-causing microbes from entering the eye, and it plays a role in immune surveillance. It also secretes tears and mucus that provide lubrication to the eye.
  4. Location: The sclera covers more than 80% of the eye, including the cornea, while the conjunctiva lines the inner surface of the eyelids and covers the sclera.

Comparative Table: Sclera vs Conjunctiva

Here is a table highlighting the differences between the sclera and conjunctiva:

Feature Sclera Conjunctiva
Location Covers more than 80% of the eye, including the cornea Covers the sclera of the eye, except the cornea
Description Thick layer that forms the white of the eye, made of dense connective tissue Thin, translucent membrane that lines the inside of the eyelid and covers the white of the eye (sclera)
Composition Composed of collagen and elastin Made up of non-keratinized, stratified columnar epithelium, stratified squamous epithelium with goblet cells, and stratified cuboidal epithelium
Function Provides structural strength and protection to the eyeball Secretes tears and mucus for lubrication, prevents entry of microbes into the eyes
Vascularization Limited blood supply Highly vascularized with many microvessels

Both the sclera and conjunctiva are essential components of the eye, serving as protective layers. However, they have different compositions and functions.