Corneal disorders

Diseases of the cornea of the eye afflict people very often, as this front part of the eye is one of the most stressed and exposed parts to external influences and risk factors. The cornea is technically called the cornea and it is the transparent part of the eyeball at the front, which is made up of connective tissue and does not contain blood vessels. The cornea is only 0.6 to 0.8 mm thick in diameter, 11.5 mm in height and 12 mm in width, and reacts reflexively to touch by closing the eyelid.

The cornea as such is composed of several layers, and since it is one of the anterior layers of the eye, it is very susceptible to various external risk factors acting on the eye from the environment. Various inflammations, sometimes even ulcerations, superficial and deeper inflammations alone or in conjunction with inflammations of other parts of the eye, as well as various degenerations, deformations or problems with the individual layers of the cornea, occur very frequently on or near the cornea.

The cornea plays a very important role in vision and the reception of visual stimuli, as it has a relatively large optical power, and thus corneal diseases cause problems with the deterioration of the quality of vision. Some are more annoying than dangerous, such as the occurrence of various ulcers, but there are also dangerous congenital or acquired disorders that can cause irreversible damage to the cornea. However, most of the diseases can be treated quite successfully, only some of them cannot yet be addressed causally by medicine.

Structure of the cornea

The cornea is the transparent and most curved part of the outer connective tissue layer of the eye, taking the shape of a horizontally placed ellipse that curves forward and occupies roughly 20 percent of the surface of the eyeball. It is colorless, without blood vessels, and constitutes both a mechanical and chemical impermeable layer between the external and internal environment. On the surface of the cornea there is a tear film whose function is to protect the corneal epithelium as well as the corners of the eye on both sides.

The cornea consists of 5 layers. The first is the anterior corneal epithelium made up of multiple layers of cells that are embedded in laminae and are non-proliferative. The second is the homogeneous Bowman's membrane formed by collagen fibers. The third layer is called the stroma of the cornea, forms the largest part of the corneal thickness and is composed of collagen lamellae. The fourth layer is Descemet's membrane, which is resistant to injury and infection. The last layer is the endothelium, which separates the cornea from the anterior chamber of the eye.

The primary function that the cornea has is to transmit and refract light, with its inner side being bathed by the internal chamber fluid, while the outer side is to protect the eye. It contains no blood vessels and is nourished just through the last layer, which comes into contact with the chamber fluid, but for this reason it is very richly innervated, contains many nerve endings, and is sensitive to mechanical as well as chemical and thermal irritation.

It reacts to various irritations by triggering the so-called corneal reflex, when the eyelid closes the eye and increased tearing of the eye, which is a defence mechanism of the cornea against the surrounding environment and external stimuli. At the edge of the visible part of the eye, the cornea also comes into contact with the conjunctiva. In terms of optical power, which is a quantity expressing the curvature of the lens and is measured in diopters, the cornea represents two-thirds of the total optical power of the eye, namely +-43 doptrees.

Inflammations of the cornea

The most common problem that afflicts most people is inflammation of the cornea. They can occur for a variety of reasons, either on an infectious basis, where viral, bacterial or mycotic infections are involved, or on a mechanical basis, where the cornea is irritated by prolonged contact lens wear, injury or insufficient tear wetting of the eye. There are several types of inflammation, most of which are superficial and acute, with a minority being deep and long-term.

The most common inflammation is keratitis, which can be areolar, superficial punctate, banded, star-shaped, nummular, filamentous, or as photokeratitis acquired from prolonged UV exposure. Other inflammations include albopsia, also called white blindness, post-exposure keratoconjunctivitis, neurotic and foveal keratoconjunctivitis, superficial keratitis with conjunctivitis, and nodular ophthalmia. Corneal inflammation also includes interstitial and deep keratitis and corneal neovascularization.

Among the inflammations of the cornea, keratitis is the most troublesome, which is a common acute inflammation, but it should not be underestimated, because if left untreated, it can cause blindness. It is most often infectious, sometimes caused by mechanical irritation of the cornea, and manifests itself in dull pain behind the eyes, burning and watery eyes and increased sensitivity to light. In some cases there is also blurred vision or eyelid spasm.

The treatment of this inflammation is topical administration of antibiotics, or symptomatically by cold compresses on the eye, and it is especially important to avoid bright light. People who wear lenses frequently can sometimes develop keratoconjunctivitis, which is most common in young people and is usually most common in the spring. Seasonally, various allergic conjunctivitises are also common and are treated by the administration of anti-allergics or, in severe cases, corticosteroids.

Scars, congestion and ulcers

In addition to inflammation, various scars, ulcers and opacities very often appear on the cornea of the eye. The most common types of ulcers found on the cornea include ulcus corneae. This is an ulcer that takes several forms and can be central, marginal, perforated, circular, with a hypopyon or as a so-called Mooren's ulcer. Various types of scars and opacities are also found on the cornea, such as central corneal opacities, unspecified corneal scars and opacities, Leucoma adhaerens and other scars and opacities.

As far as ulcers are concerned, corneal ulcers are caused by the breakdown of the epithelium on the surface of the cornea, with an inflammatory process that spreads both superficially over the cornea and deep into the cornea. If this inflammatory process is stopped, a scar on the cornea will occur, which will naturally deteriorate the transparency of the cornea. Inflammation may even occur subsequently. If the inflammatory process is not stopped, a bulging and rupture of the membrane in the middle of the cornea and a window into the cornea occurs.

Fortunately, such scars and opacities can nowadays be removed and repaired thanks to modern medicine, especially with the help of modern laser corneal surgeries, but this is not fully true for every scar or opacity. One of the rather complex bases is Leucoma adhaerens, which is a type of white corneal cataract that is also considered a so-called white tumour on the edge of the cornea and which also causes a disruption of the natural transparency of the cornea and thus a deterioration of vision.

Corneal opacities are also caused by various external factors, such as damage caused by chemical splashes on the cornea or mechanical trauma causing necrosis of the cornea and some of its epithelial tissues.Very often, both corneal opacities and corneal necrosis arise from an infectious background, for example, smallpox, as a complication of the latter. If the corneal opacity is only minor, it may sometimes not even show any symptoms, but if the vision is disturbed, the procedure used is either abrasion of the upper layer of the cornea or straight corneal transplantation.

Changes on the cornea

Various changes or disorders or diseases occur in the cornea also due to non-inflammatory causes. For example, corneal pigmentations and corneal deposits such as haematocornea, Kayser-Fleischer ring or Krukenberg's spindle, various corneal degenerations such as gerontoxon or corneal band opacities, corneal edema and hereditary corneal dystrophies are also common. Dystrophy can be epithelial, granular, reticular or mottled.

As such, dystrophies are the primary disease of the eye and, although rare, occur most often by heredity and usually bilaterally. They manifest themselves relatively early in adolescence and tend to worsen over the course of life. Epithelial dystrophies are most often manifested by corneal erosions and pain, and very often return after laser treatment. In some cases, there is also a slight deterioration of vision and the sensation of a foreign body in the eye.

Stromal dystrophy, on the other hand, is manifested by a significant reduction in visual acuity and often by the subsequent progression of this deterioration, which is also painful and recurrent. Surgery is also the only effective solution for this dystrophy. Endothelial dystrophy is also a severe form of dystrophy, where there are changes in the cornea and also epithelial bullae, and can also be associated with the appearance of haze, pain and oedema.

The corneas may also be affected by various pigmentations or degenerations of shape. Corneal deformities and changes affecting the cornea include corneal ecstasia and staphyloma and herniation of Descemet's membrane. In most cases, the only solution to these diseases is surgery to repair the cornea; in rare cases, transplantation of a new artificial cornea is necessary due to the extent of the damage or long-term irreversible changes to the cornea.

Other corneal diseases

In addition, the cornea is also affected by various types of corneal degeneration, such as keratoconus, keratoglobus or pelucid marginal degeneration. These are secondary-onset diseases that most often arise when a person is advanced in age and can sometimes be conditioned by other systemic diseases. The most common deformity is conical bowing of the thinned cornea either centrally or paracentrally, and this degeneration is gradual in nature.

In most cases, it is bilateral and often occurs in combination with, for example, atopic dermatitis or Down's, Turner's or Marfan's syndrome. In addition to degeneration, the cornea may be affected by anaesthesia, hyperesthesia or various types of recurrent corneal erosions. Diseases also damaging the cornea include scleritis, episcleritis, herpetic keratitis or keratoconjunctivitis arising from tuberculosis, syphilis or other epidemic causes.

The pterygium, which is a fleshy growth originating from the conjunctiva, sometimes overgrows through the central cornea. However, this defect does not occur very often in our country. In rare cases, squamous cell carcinoma, which is a malignant tumour similar to skin cancer, can occur not only on the cornea but also on the eyelid or conjunctiva. It most often passes here from the eyelid and mainly affects people of older age.