What is Sclera?
The Sclera is known to be the white part of the eye surrounding the corona. It covers almost 80% of the area of the eye that the sclera covers, starting from the cornea and extending to the optic nerve. The optic nerve is extended to the back portion of the eye. We can only see a very little portion of the sclera as we can also see the eyeball. The sclera is actually what is the white part of the eye called. Now that we know what is the sclera, let us learn its functions and related issues in detail.
Sclera of Eye
The sclera of the eye is one type of connecting tissue continuing with the stroma layer of the corona. Limbus is known to be the connection part between the clear cornea and the white sclera. The thickness of the sclera ranges from 0.3 mm up to 1 mm. It is made up of small fibres or fibrils of collagen that are generally interlacing and irregular bundles. The flexibility and strength of the eyeball depend on these connective tissues as these form an interweaving arrangement. The sclera has a limited supply of blood and so is usually metabolically inactive. Though sclera has no blood vessels or is known to be avascular, many blood vessels pass through it.
Episclera is a thin layer of connective tissue present in the top of the sclera, the white part of the eye. It’s that transparent conjunctiva that covers the part of the episclera and sclera. It also generates some blood vessels, which are the primary reason for the nourishment of the sclera. Underlying chloride is another reason for the nourishment of sclera. Chloride is nothing but one vascular layer from the eyeball that’s placed between the retina and sclera.
Function of Sclera
It maintains the proper function of the eye or eyeball. Intraocular pressure (IOP) also helps in the same sclera function.
It protects the eye from any serious damage that might happen from rupture or laceration.
It also protects the eyeball from any external trauma.
Extraocular muscles are responsible for eye movement. The sclera provides one type of sturdy attachment to these muscles. This is another important sclera function. It helps to locate the sight, particularly where one individual is looking. It makes it easier when it comes to non-verbal communication.
Low-velocity injury can’t go through the sclera.
It is rarely injured by heat hence protecting the eye indirectly.
The sclera is also resistant to toxic chemicals, thereby protecting the eye. The reflexive mechanism that is tears easily wash away the chemicals. Sclera eye function protects the eye in many ways.
Different Problems Related to the Sclera
Scleral Icterus or yellow eyes is one eye condition where the sclera becomes yellowish. This happened when someone got liver issues or hepatitis. Though there is some controversy regarding the fact where researchers state that jaundice or yellowing of the eye actually occurs in the part of the conjunctiva. However, many doctors call such issues scleral icterus. Bilirubin or blood serum increment is known to be the reason for jaundice or yellow eye. If you have any such issues immediately, the doctor's suggestion would be to do a blood test that will identify the issue if it's related to a liver problem or not.
Blue Sclera is thinning of sclera from any kind of disease that finally shows choroidal issues that appear through it. Hereditary and congenital diseases are the main reason for such conditions. Brittle bone disease (osteogenesis imperfect) and connective tissue disorder or Marfan's syndrome are some of the reasons. Anaemia or iron deficiency can also cause blue sclera.
Episcleritis or episclera inflammation is a common disease associated with the sclera. This has two types. One is nodular episcleritis, and another is simple episcleritis. The former one is the redness of the overlying tissue portion of the sclera. Later one happens when dilated blood vessels (episcleral) occur in the presence of a nodule. But the fact is most of the reasons for episcleritis are yet unknown. But a few people who get this condition generally go through systematic disorders like rheumatoid arthritis, rosacea, ulcerative colitis, gout, etc.
Scleritis is one eye condition where both episclera and underlying sclera inflammation starts. This is a red-eye condition with a painful situation. This also is the reason for systemic diseases. This can cause vision loss conditions even permanent damage to the eyes.
FAQs on Sclera
1. What is the sclera and what are its primary functions in the human eye?
The sclera is the tough, fibrous, white outer layer of the eyeball that covers approximately 80% of its surface. Commonly known as the 'white of the eye,' its main functions are to:
- Provide structural support and maintain the shape of the eyeball.
- Protect the delicate internal components of the eye from injury and external threats.
- Serve as an attachment point for the extraocular muscles that control eye movement.
2. What is the normal colour of a healthy sclera, and why might it change?
A healthy sclera is normally an opaque, white colour. However, its colour can change due to various underlying conditions. A yellowish sclera may indicate jaundice, which is related to liver problems. Redness or inflammation can be caused by irritation, allergies, or conditions like scleritis and conjunctivitis. A bluish tint can sometimes be seen in infants or in certain connective tissue disorders.
3. How does the sclera differ from the cornea?
The sclera and cornea are both part of the eye's outer layer, but they have key differences:
- Transparency: The cornea is transparent to allow light to enter the eye, while the sclera is opaque and white.
- Location: The cornea is the front, central part of the eye covering the iris and pupil. The sclera forms the rest of the outer coat.
- Function: The cornea's primary role is to refract (bend) light, contributing to the eye's focusing power. The sclera's primary role is protection and structural support.
4. What is the difference between the sclera and the conjunctiva?
The main difference lies in their nature and location. The sclera is the thick, white structural wall of the eyeball itself. The conjunctiva, on the other hand, is a thin, transparent mucous membrane that covers the front surface of the sclera and lines the inside of the eyelids. While you see the white sclera, you are looking at it *through* the clear conjunctiva.
5. What are the different layers of the sclera?
The sclera is composed of three main layers, from outermost to innermost:
- Episclera: The outermost layer, rich in blood vessels that provide nourishment.
- Scleral Stroma: The middle layer, made of dense collagen fibres that give the sclera its strength and white colour.
- Lamina Fusca: The innermost layer, which contains pigment cells and connects the sclera to the underlying choroid.
6. What happens if the sclera is damaged?
Damage to the sclera can be very serious. A minor injury might cause redness and pain (scleritis). However, a significant injury, such as a laceration or rupture, can be a medical emergency. It can lead to severe pain, vision loss, and leakage of the eye's internal fluid. Such damage compromises the eye's structural integrity and can lead to complications like retinal detachment or severe infection, potentially resulting in blindness if not treated immediately.
7. How do muscles attach to the sclera to enable eye movement?
The six extraocular muscles, which are responsible for moving the eye in all directions, attach directly to the outer surface of the sclera. The tough, fibrous nature of the scleral stroma provides a firm and stable anchor for these muscles. When these muscles contract and relax in coordination, they pull on the sclera, causing the entire eyeball to rotate within the eye socket, allowing us to look up, down, and side-to-side.
8. What is the importance of a scleral lens in vision correction?
A scleral lens is a large-diameter, specialised contact lens that rests on the sclera and vaults over the cornea without touching it. This design is highly beneficial for individuals with irregular corneas (e.g., due to keratoconus) or severe dry eye. The lens creates a new, perfectly smooth optical surface over the damaged cornea, and the space between the lens and cornea is filled with a saline solution, which keeps the eye hydrated and provides exceptionally clear vision.
9. What is a 'scleral buckle,' and is it a part of the sclera?
A scleral buckle is not a part of the sclera; it is the name of a surgical procedure used to repair a detached retina. In this procedure, a surgeon places a small band of silicone or plastic onto the outside of the sclera. This band pushes, or 'buckles,' the sclera inward, which helps the detached retina reattach to the inner wall of the eye. The name refers to its effect on the sclera, but its purpose is to treat the retina.
