Inflammation of the cornea (keratitis)

Inflammation of the cornea (keratitis) is primarily caused by infection with bacteria or viruses. Those who wear contact lenses or have a weakened immune system are at greater risk

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Corneal inflammation - briefly explained

In the case of corneal inflammation (keratitis), the front, transparent cover over the eye becomes inflamed. In the majority of cases, the cause is bacteria, mostly in contact lens wearers. Viruses, fungi, dry eyes, superficial eye injuries or a weakened immune system are also possible triggers. Depending on the cause, keratitis can develop very differently. If the inflammation is limited to the surface of the cornea, a slight opacity develops. If deeper layers become inflamed, a denser cloudiness forms on the affected area, which can appear as a whitish stain. A corneal inflammation usually leads to considerable pain and a reddened eye, since the conjunctiva is usually inflamed at the same time (keratoconjunctivitis). Therapy depends on the cause of the inflammation. If the keratitis is caused by bacteria, for example, the ophthalmologist will prescribe eye drops containing antibiotics. Corneal scars, corneal ulcers (ulcers) or inflammation of the inside of the eye (iris inflammation, accompanying inflammation) can occur as complications of keratitis.

What is corneal inflammation (keratitis)?

With keratitis, one or more layers of the cornea become inflamed - see also the background information.

© Fotolia / Vanessa

Background information: location and function of the cornea

The cornea is the front, transparent, curved part of the outer skin of the eye. You can compare it to the glass of a wristwatch. So it forms the front cover of the eye and protects it. It is washed around, cleaned and nourished by the tear fluid and is significantly involved in the refraction of light.

Structure of the cornea

The cornea, together with the sclera, form the outer covering of the eye. The cornea is made up of three layers, none of which contain blood vessels. The outer layer - the epithelium - together with the tear film protects the eye from bacteria and foreign bodies. The middle part, the stroma, consists of a layer of tissue. Due to the high water content (75 percent) and the regular arrangement of the so-called stromal lamellae, the cornea appears transparent. Underneath is the so-called Descemet membrane, on which the inner layer of the cornea (endothelium) lies. It is made up of elastic fibers and is therefore particularly resistant. The endothelial cells can be thought of as small pumps that permanently pump water out of the cornea and thus play a decisive role in transparency. The clarity of the cornea in combination with a clear eye lens is extremely important for the sharp image of objects on the retina.

Causes: How does corneal inflammation (keratitis) occur?

The most common form of bacterial keratitis. Typical germs are staphylococci, streptococci and pneumococci. If the cornea is intact, the inflammation is mostly limited to the surface of the cornea. However, if there are small, external defects on the cornea - for example after a superficial injury from a branch - the pathogens can penetrate into deeper layers of the cornea. In around 30 percent of bacterial corneal inflammation, those affected wear contact lenses.

In addition to bacteria, viruses can also be considered as triggers. Usually these are herpes simplex viruses, varicella-zoster viruses (chickenpox viruses) or adenoviruses. Over 90 percent of Germans are carriers of the herpes simplex virus without being aware of it. Because the virus often does not trigger any symptoms, but lingers "calmly" in the body. In some people, however, there is an infection with symptoms. The herpes labialis causes the typical lip vesicles. Depending on the nerve pathways in which the viruses stay, reactivation of the "dormant" viruses can lead to recurring herpes keratitis (relapse). This happens, for example, when the immune system is temporarily weakened or the patient uses eye drops containing cortisone in an uncontrolled manner and over a long period of time.

Fungi and parasites (amoebas) rarely cause corneal inflammation.

Germs are not always the cause of an inflamed cornea. If the eye is not properly wetted, for example because the lacrimal glands produce too little tear fluid (dry eye) or the quality of the tear film is reduced, this can roughen the surface of the cornea. This can result in what is known as superficial punctate keratitis. Lid misalignments can also contribute to this due to the resulting disturbance in the distribution of the tear film.

Symptoms: What symptoms does corneal inflammation (keratitis) cause?

Corneal inflammation can take very different courses, depending on the cause and location. In principle, any corneal layer can become inflamed - i.e. the epithelium, stroma and / or the endothelium. If the outer layer of the cornea (epithelium) is inflamed, a gray-whitish opacity develops on the surface of the cornea. If the inflammation affects the underlying thickest layer of the cornea (stroma), there is an infiltrate that appears as a whitish spot. If the innermost layer, the endothelium, is affected, the cornea can swell. The eyesight is in any case more or less impaired.

If bacteria cause corneal inflammation, patients complain of intense pain in the eye and are afraid of light. In addition, the lid tightens (blepharospasm). Usually conjunctivitis (conjunctivitis) occurs at the same time, which manifests itself as a reddened and watery eye. Often the affected eye also secretes a watery or purulent secretion.

If the pathogens penetrate deeper layers of the cornea, an ulcer (corneal ulcer) can develop. In particular, the "creeping ulcer" (Ulcus serpens) can be very dangerous. If left untreated, it can lead to inflammation of the iris (iritis) with accumulation of pus in the anterior chamber of the eye.

In the worst case, the ulcer can break inward and eye fluid (aqueous humor) escapes to the outside.

If herpes viruses (herpes simplex virus) are behind keratitis, there is often an unpleasant foreign body sensation in the eye. Here, too, it hurts and is reddened.

A fungal infection is insidious and causes fewer symptoms - apart from the fact that the eyesight is reduced.

If a corneal inflammation occurs due to a "dry eye", the affected eye is reddened. The patients also have the feeling of having a grain of sand in their eye that rubs with every movement.

Diagnosis: how is corneal inflammation diagnosed?

If corneal inflammation is suspected, the doctor first clarifies what symptoms the patient is experiencing, asks about previous inflammations and checks the visual acuity.
He then examines the cornea with a slit lamp. This device is a kind of microscope with which the ophthalmologist can view all layers of the cornea with a magnification of up to 40 times. With the help of the slit lamp he can detect possible injuries on the surface (epithelium) as well as changes in the middle (stroma) or inner layer (endothelium) of the cornea.

If the doctor suspects bacterial corneal inflammation based on the symptoms, he or she can take a swab from the cornea and conjunctiva. The ophthalmologist has the sample examined for bacteria. In this way, he firstly determines whether bacteria have actually triggered the keratitis. Second, the type of pathogen and the appropriate therapy can be determined in the laboratory. Fungi are detected in a similar way. In principle, the eye specialist can also detect viruses, but this is much more time-consuming.

In addition, the doctor can stain the corneal surface with special dyes (fluorescein or rose bengal). This allows changes on the cornea to be discovered - also with the aid of the slit lamp. At the same time, the staining method enables information about the quality of the tear film to be obtained. If the eye is not sufficiently wetted, the color will not remain on the eye for enough time. The ophthalmologist uses the so-called break-open time to determine whether the tear film is composed normally or not.
If the doctor suspects that there is a "dry eye" behind the keratitis, he may use the "Schirmer test". With this method, he measures how much tear fluid is produced. To do this, a narrow strip of filter paper is hung in the conjunctival sac between the lower eyelid and the eyeball. If less than ten millimeters of the strip is moistened after five minutes, this indicates impaired tear secretion.

Therapy: How is corneal inflammation treated?

In most cases, bacteria cause keratitis. In this case, the doctor will prescribe eye drops that contain antibiotics. These agents inhibit the pathogen from multiplying.

If there is an infection with herpes viruses, the ophthalmologist usually uses the active ingredient acyclovir. This helps against herpes simplex viruses, but also against chickenpox viruses. The drug can be used in a combination of eye ointment and oral tablets.

If a "dry eye" leads to corneal inflammation, artificial tears are used. These are special eye drops that wet the eye and thus keep it moist. This stabilizes the tear film that protects the corneal surface. These drops need to be used frequently and often over a long period of time.

If a corneal ulcer occurs, this requires intensive antibiotic and anti-inflammatory therapy with eye drops and possibly tablets. The ophthalmologist must closely monitor the treatment. This may be done in a hospital. A corneal ulcer is always an emergency situation, as the eye is acutely threatened.

A newer surgical treatment option for a corneal ulcer is amniotic transplantation - sewing an amniotic membrane onto the corneal surface. The amnion is the innermost part of the human membrane or amniotic sac and is available after every delivery. The amniotic membrane acts like a biological bandage, it has anti-inflammatory and anti-scarring properties and enables a corneal ulcer to heal more quickly. However, scarring of the cornea can usually not be prevented. The amniotic tissue dissolves on its own within a few weeks.

Prevention: How can corneal inflammation be prevented?

Tips on contact lens care

Soft contact lenses, in particular, are susceptible to germs, as the plastic material soaks up tear fluid and provides ideal growth conditions for pathogens. Therefore, you should absolutely adhere to a few hygiene rules:

  • Wash hands with soap and dry them before handling the lenses
  • Never clean the lenses with tap water but always carefully disinfect them with a suitable agent
  • Clean the lenses again if you haven't used them for more than a week
  • Use care products only once for cleaning
  • Periodically rinse the lens case with sterile storage solution and allow to dry
  • replace the lens case at regular intervals

If contact lenses are worn for too long or are not cleaned thoroughly, bacteria can easily settle on the lenses and get into the eye. Leaving contact lenses in the eye overnight should also be avoided. Furthermore, a weak immune system, for example in the elderly, or diseases such as diabetes mellitus promote bacterial keratitis.

Prof. Thomas Klink

© W & B / private

Our advisory expert:

Professor Dr. med. Thomas Klink has been working at the Herzog Carl Theodor Eye Clinic and in the group practice there in Munich since July 2015. Previously, as the senior physician at the University Eye Clinic in Würzburg, he had already dealt scientifically and clinically with diseases of the anterior segment of the eye.


  • Karen S DeLoss, ODH; Kaz Soong, MD; Christopher T Hood, MD. Complications of contact lenses. Post TW, ed. UpToDate. Waltham, MA: UpToDate Inc. (accessed March 26, 2020)
  • Deborah S Jacobs, MD. Overview of the red eye. Post TW, ed. UpToDate. Waltham, MA: UpToDate Inc. (accessed March 26, 2020)

Important NOTE:
This article contains general information only and should not be used for self-diagnosis or self-treatment. He can not substitute a visit at the doctor. Unfortunately, our experts cannot answer individual questions.

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