Corneal diseases

The cornea 

The cornea is the transparent, crystal clear and translucent frontmost section of the eyeball and is located in front of the pupil.  In a healthy condition, it is about half a millimetre thick. With its natural curvature, it contributes two-thirds of the refractive power of the eye, together with the lens. 

The cornea is often referred to as the “protective screen” of the eye, as it is also responsible for protecting the eye against external aggressors. For this reason, diseases of the eye that affect the transparency or shape of the cornea can lead to serious visual impairments, which is why they require consultation with an ophthalmologist. 

Causes

Causes of corneal disease include inflammatory processes of an infectious and non-infectious nature, degenerative and hereditary changes of the cornea. Injuries and changes as a result of medical treatment can also lead to corneal disease. The individual diseases of the cornea and their causes at a glance: 

• Corneal injuries ( corneal erosion): An erosion is the abrasion of the uppermost layer of cornea. This can be caused by superficial injuries (e.g. by a fingernail or a thin splinter) or by contact lenses worn for too long or which are badly fitting. The exposed nerve endings cause severe pain and lead to increased lacrimal flow, redness, light sensitivity and swelling of the eyelid. Vision may also be significantly impaired. 
• Inflammation of the cornea (known as keratitis): Inflammation of the cornea can occur as a result of external aggressors when pathogens enter the cornea. The symptoms are similar to those of an erosion (corneal injury) and are treated by eye drops, eye ointments and, if necessary, tablets. However, keratitis can also occur without an external injury, i.e. from the inside, as the result of other eye diseases, such as inflammation of the iris or as a consequence of general illnesses (especially rheumatism). This type of keratitis is not without its dangers, as pain and sensitivity to light are often lacking. The only symptom is usually the deterioration of vision. It is important to consult an ophthalmologist immediately if keratitis is suspected. 
• Corneal ulcers: A corneal ulcer is a sore on the cornea. It is usually caused by a lesion of the uppermost layer of the cornea through which pathogens can penetrate the cornea and destroy the tissue of the cornea. Two possible serious complications make corneal ulcers an absolute emergency, as they can lead to a perforation of the cornea and thus to a transmission of the pathogens to the inside of the eye, leading to the risk of blindness or even loss of the eye. Corneal ulcer is very often painful and is accompanied by redness, increased lacrimal flow, light sensitivity and eyelid spasm. Vision is usually significantly restricted. 
• Corneal scarring: Irrespective of whether scarring is caused by keratitis, an ulcer, deeper erosion or injuries, it can significantly impair vision.  
• Corneal degeneration: Corneal degeneration includes changes to the cornea that may occur as a result of ageing or after corneal diseases or injuries. As the cornea loses its transparency, vision is significantly reduced in some cases. 
• Corneal dystrophy: Corneal dystrophies are usually bilateral congenital changes of the cornea. These changes can occur in any layer of the cornea. Some do not cause visual impairment, but others, such as Fuchs’ dystrophy, can affect vision considerably. 
• Keratoconus (i.e. the pathological, conical bulge of the cornea that can progress gradually): This condition first becomes apparent through frequent changes in the strength of your glasses, although myopia can never be completely corrected. Double vision, and streaks and starburst rays may also appear in the vision. 
• Corneal grafting (keratoplasty): If conservative treatment attempts using eye drops fail to fade the scarring, it must be surgically removed. 

Treatments

The individual corneal diseases require different treatment methods. Specifically, these are: 

• Inflammation of the cornea: Inflammation of the eye is treated with eye drops, eye ointments and, if necessary, tablets.  
• Cornea injuries: Intensive treatment with eye drops or eye ointment or bandage contact lenses often helps to heal a corneal injury without scarring. However, if the injury does not heal despite treatment, an amniotic membrane covering may be necessary. The amniotic membrane is a tissue obtained from the placenta, which is sewn onto the open area of the cornea. 
• Corneal ulcers: A corneal ulcer is generally treated using eye drops or ointments and possibly tablets. However, if an ulcer does not heal, an amniotic membrane covering may also be necessary. If perforation occurs, it must be surgically sealed immediately. If the inflammation reaches the inside of the eye, surgical irrigation of the eye may also be necessary. 
• Corneal scarring: If drug therapy attempts using eye drops do not fade the scar, surgery must be considered, depending on the patient’s symptoms and impairment. In the case of superficial scars, the scar tissue can be removed by means therapeutic scraping of the corneal epithelium, i.e. the uppermost cell layer of the human cornea. In the case of deep scars, on the other hand, only corneal transplantation is promising. 
• Corneal degeneration: Corneal degeneration is treated by EDTA chelation. Under local anaesthesia, after removal of the uppermost layer of cornea, the calcium deposits in the cornea are removed using EDTA (ethylenediaminetetraacetic acid). 
• Corneal dystrophy: In early stages of this disease, vision improves over the course of the day, as water from the cornea surface can evaporate when the eye is open. In addition, special eye drops or eye ointments can be used to “draw water from the cornea.” However, it should be noted that this type of therapy can only delay the course of the disease, but not completely stop it. 
• Keratoconus: In early stages of the disease, patients often have the strength of their glasses and/or contact lens prescription frequently adjusted. However, as soon as the disease is more advanced and neither glasses nor contact lenses can provide an improvement, surgery or even a corneal transplant becomes necessary. 
• Corneal grafting: Keratoplasty is an operation of the cornea in which the cornea of a dead donor is transplanted. If the ophthalmologist has determined the need for a corneal transplant, suitable donor tissue is sought in a cornea bank. The actual operation is performed either under local anaesthesia or under general anaesthesia. Depending on the degree of clouding on the patient’s cornea, the ophthalmologist can either fully or partially remove it. They then cut the donor cornea to size and suture it to the patient’s eye. The sutures remain in the eye for several months to years, as wounds heal very slowly in this area.