Sclera

The Sclera or Dermis is part of the eye and spans a large part of the eyeball. It mainly has a protective function.

What is the sclera?

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

This phenomenon occurs especially in infants. As the area cribrosa, the sclera begins at the point of entry of the optic nerve on the back of the eyeball. At this point the sclera has fine openings through which several blood vessels lead. In addition, the sclera and Tenon's capsule connect at this point. The Tenon's capsule delimits the sclera from the outside and separates it from the surrounding fatty tissue. The Tenon capsule allows the eye to move freely in different directions. At the front of the eye, the sclera surrounds the cornea of the eye and forms a bulge called the scleral bulge 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 kept in shape by the internal pressure of the eye.

The lamina episcleralis rests on the substantia propria as a second layer. It is permeated by numerous blood vessels and thus plays an important role in the supply of nutrients and oxygen. Inwardly, the substantia propria covers another layer of tissue, the lamina fusca. The lamina fusca is very thin and contains pigments. In addition, the lamina fusca establishes the connection to the choroid below the sclera, through which the majority of the blood vessels in 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. The sclera mainly protects the choroid (choroid) underneath it, which contains numerous sensitive blood vessels.

In order not to obstruct the blood supply, there are openings in the sclera for blood vessels or connecting veins to pass through. This is especially the case in the front part of the eye, where the sclera on the cornea forms the scleral bulge. Numerous blood vessels run through the scleral bulge at the binding point 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: Based on its color, various diseases can be inferred.

In the case of liver disease or infection with jaundice, the otherwise white sclera turns white-yellowish to deep yellow. This discoloration is not a disease of the eye, but an early sign of another disease. After treating the cause, the sclera turns white again. Diseases that, in addition to jaundice, typically lead to a yellow discoloration of the sclera are hepatitis, alcoholism, and malnutrition or malnutrition. The substance bilirubin is responsible for the yellow coloration. It is created when the red hemoglobin is broken down, which turns the blood red. Dark spots in the sclera provide evidence of the tyrosine metabolic disease alkaptonuria.

Diseases

The majority of the typical diseases of the sclera are inflammations. Medical professionals commonly refer to this inflammation as scleritis. If only the top layer of the sclera is inflamed, it is 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 human body. Autoimmune diseases such as rheumatism or gout are among the most common triggers. For example, the body's immune system confuses the collagen connective tissue of the sclera with a potentially harmful substance and attacks it. The symptoms of inflammation such as swelling, redness and itching are the result of this attack on the own immune system.In rarer cases, inflammation of the sclera can result from a localized infection.

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

If the sclera or another part of the eye or face is affected, medical professionals refer to the infection as ophthalmic zoster. 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, these days, syphilis can be treated well with the help of antibiotics. Blood poisoning (sepsis) can also lead to inflammation of the sclera. Blood poisoning is a so-called systemic inflammatory reaction that attacks numerous organs at the same time.