Anatomy & Organs

Sclera – structure, function & diseases

Sclera

The sclera or sclera is part of the eye and encloses a large portion of the eyeball . It mainly has a protective function.

What is the sclera?

The sclera encompasses almost the entire eye and shimmers white through the conjunctiva . For this reason, it is less commonly referred to as white eye skin. A thin sclera can cause the eye to appear slightly bluish.

This phenomenon occurs especially in infants. As the area cribrosa, the sclera begins at the entry point of the optic nerve on the back of the eyeball. At this point, the sclera has fine openings through which several blood vessels pass. In addition, the sclera and Tenon’s capsule connect at this point. Tenon’s capsule externally demarcates the sclera and separates it from the surrounding adipose tissue . The Tenon’s capsule allows the eye to move freely in different directions. At the front of the eye, the sclera encloses the cornea of ​​the eye , forming a ridge called the scleral ridge or sulcus sclerae.

Anatomy & Structure

The sclera consists of several layers: in the center is the substantia propria, which consists of collagen connective tissue. It is stretched and held in shape by the internal pressure of the eye.The lamina episcleralis is the second layer over the substantia propria. It is traversed by numerous blood vessels and thus plays an important role in the supply of nutrients and oxygen. Inward, the substantia propria encases another layer of tissue, the lamina fusca. The lamina fusca is very thin and contains pigments. In addition, the lamina fusca connects to the choroid beneath the sclera, through which most of the blood vessels of the eyeball flow.

Function & Tasks

The main function of the sclera is to protect the eye. It shields the eye from mechanical influences and direct sunlight and gives it stability. Above all, the sclera protects the underlying choroid (choroid), which contains numerous sensitive blood vessels.

In order not to impede the blood supply, there are openings in the sclera for blood vessels to pass through or connecting veins. This is especially the case in the front part of the eye, where the sclera forms the scleral ridge on the cornea. Numerous blood vessels run through the scleral bulge at the junction between the cornea and the sclera. They play an important role in supplying nutrients to the other parts of the eye. The sclera also has a function as an indicator of the general state of health: its coloration can be used to draw conclusions about various diseases.

In the case of liver disease or an infection with jaundice , the otherwise white sclera turns white-yellowish to deep yellow. This discolouration is not a disease of the eye, but an early sign of another disease. After treating the cause, the sclera turns white again. Disorders that typically cause yellowing of the sclera, other than jaundice, include hepatitis , alcoholism , and malnutrition . The substance bilirubin is responsible for the yellow colouration. It is formed during the breakdown of red hemoglobin , which makes up the bloodcolors red. Dark spots in the sclera provide evidence of the tyrosine metabolic disease alkaptonuria.

Diseases

The majority of typical diseases of the sclera are inflammations . Medical professionals refer to this inflammation as scleritis . If only the top layer of the sclera is inflamed, it is an episcleritis – named after the outermost layer of the sclera, the lamina episcleralis.Scleritis is usually caused by another disease that affects other parts of the body. Autoimmune diseases such as rheumatism or gout are among the most common triggers. For example, the body’s immune system mistakes the collagen connective tissue of the sclera for a potentially harmful substance and attacks it. The symptoms of inflammation such as swelling , redness and itching are the result of this attack by the body’s own immune system. In rarer cases, inflammation of the sclera may result from localized infection.

Micro-injuries to the eye can trigger such a local infection if bacteria enter the wound . Other infectious diseases can also appear as a result of the inflammation of the sclera. Borreliosis can also cause corresponding tissue damage as Lyme disease Lyme disease is an infectious disease caused by bacteria in humans and some animals. The most common carriers of these bacteria are ticks , and more rarely certain types of mosquitoes. In the case of shingles (herpes zoster), an infection with the corresponding virus causes inflammation in the affected parts of the body.

When the sclera or other part of the eye or face is affected, doctors refer to the infection as zoster ophthalmicus. If the eye is infected with the herpes zoster virus, there is a risk of permanent blindness , since the cornea can become cloudy or otherwise damaged as the disease progresses. Syphilis can also lead to inflammation of the sclera. This sexually transmitted disease was a widespread and feared infectious disease from the Middle Ages to modern times. However, syphilis can now be effectively treated with antibiotics . In addition, blood poisoning(sepsis) also lead to inflammation of the sclera. Blood poisoning is a so-called systemic inflammatory reaction that attacks numerous organs at the same time.

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Hello! I am Lisa Newlon, and I am a medical writer and researcher with over 10 years of experience in the healthcare industry. I have a Master’s degree in Medicine, and my deep understanding of medical terminology, practices, and procedures has made me a trusted source of information in the medical world.