Cornea and Corneal Disease

The cornea is the clear external layer of the eye, through which you can see the coloured iris and the pupil.

The cornea is made of six different layers, including:

The epithelium (the outermost layer).
Basement membrane.
Bowman’s layer.
The stroma (the middle layer).
Descemet’s membrane.
The endothelium (the inner layer).

What does the cornea do?

The cornea is like a window and allows light to pass through to the retina, which is located at the reverse side of the eye. Light rays are refracted by the cornea, focused by the lens and then projected onto the retina, forming an image which is then transmitted to the brain. If the cornea is injured this will reduce the sum of light that passes through to the retina and cause the image transmitted to the brain to become blurred or distorted.

The cornea also has a protective role, and as the outermost layer of the eye it helps to protect the other parts of the eye from dust and harmful germs. The cornea also helps to protect the eyes from harmful UV light rays.

Injuries to the cornea

The cornea is tough and hard-wearing and it tends to respond to minor injuries fairly well. However, if the cornea is severely damaged it can be very painful and symptoms can be unpleasant. If the cornea is scratched, this can result in redness, swelling, blurred vision and tearing. The cornea can also become sensitive to light, which can increase pain.

Conditions and illnesses that affect the cornea

There are a number of illnesses and conditions which can affect the cornea. Here are a host of the most frequently seen conditions:

Allergies

Allergies that influence the eyes are common and many people experience red, swollen and itchy eyes when they come into contact with an allergen. The most common allergy that triggers symptoms in the eyes is hay fever (an allergy to pollen and grass). Most allergies are mild and can be controlled effectively with antihistamine medication. However, it is also advisable to wear sunglasses to protect your eyes if you go out and avoid leaving windows open in the spring and summer months when the pollen count is high. Wearing contact lenses can also cause allergies so if you experience soreness, redness or itching, you should see an optometrist as soon as possible. They can change your contact lenses or recommend an alternative treatment.

Conjunctivitis

Conjunctivitis is a very common condition, which causes the eyes to become itchy, red and swollen. Conjunctivitis is contagious and you should avoid touching your eyes if you have the condition. In most cases the infection will clear up without requiring treatment, but eye drops or ointment may be recommended if the infection does not clear on its own.

Infections

The corneas can become inflamed and infected following injuries, wearing contact lenses or exposure to foreign bodies. Infections affecting the cornea are known as keratitis. Keratitis can cause eye discharge, pain and swelling, as well as making your vision unclear. Corneal infections can become very serious if they are left untreated and may cause irreversible damage. In most cases infections can be effectively treated by antibacterial eye drops and ointments and, in severe cases, steroid drops may be prescribed to reduce inflammation.

Dry eye

Dry eye is a common condition which occurs when tear production is decreased or the tears evaporate too quickly, leaving the eyes dry. Symptoms of dry eye include itchiness, sore and dry eyes, a gritty feeling in the eye, stinging and blurred vision. Dry eye is most common in people over the age of 60 and it is more common among women than men. Dry eye is regularly a mild condition and it can be brought on by other conditions, including blepharitis and more complex medical conditions, such as HIV or lupus, in addition to environmental factors.

There is no cure for dry eye but there are treatments that can ease symptoms, including eye drops to mimic the role of tears, eye ointment to lubricate the eyes and specially manufactured moisture chamber spectacles. If dry eye is caused by an underlying health condition, treating this condition will usually ease symptoms of dry eye. If other treatments fail surgery may be carried out. There are two types of procedure that can be used, including punctual occlusion to seal the tear ducts closed and salivary gland autotransplantation, which involves removing glands from the lip and implanting them into the eyes.

Fuchs’ dystrophy

This is an uncommon condition which causes the Descemet’s layer of the cornea to degenerate. The disease is progressive and seldom affects sight until people arrive at the age of 50, although most people start to notice early signs during their 30s or 40s. Fuchs’ dystrophy causes the endothelial cells in the cornea to degenerate, which prevents them from removing fluid from the stroma (the middle section of the cornea) and causes the cornea to become swollen. If the cornea swells, this affects vision. As the condition progresses the epithelium also becomes affected and this can cause serious visual impairment.

During the early stages of Fuchs’ dystrophy symptoms include blurred vision, which usually improves over the course of the day. However, as the condition progress vision may become distorted all day and will eventually become worse. The primary aim of treatment is to reduce swelling, which can be done by using eye drops and ointments. As the disease progresses and symptoms become worse, a corneal transplant may be required.

Corneal dystrophies

There are more than 20 different types of corneal dystrophy, but they all have the same characteristics, including:

They are inherited conditions.
They affect both eyes.
They are not brought on by environmental factors.
They develop gradually.
They do not usually influence other areas of the body.

Herpes Zoster

(more commonly known as shingles)

Shingles is caused by the varicella-zoster virus, which is also responsible for causing chickenpox. Shingles occurs when the virus is reactivated following a bout of chickenpox; however, shingles tends to be much more unpleasant than chickenpox and can make people feel very ill. Symptoms of shingles include a blistered rash, itchiness, generally feeling unwell, muscle pain and a fever (high temperature). Shingles is usually treated with anti-viral medication, painkillers and calamine lotion to ease symptoms and bring body temperature down. The virus affects the cornea in around 40 percent of individuals with shingles and causes the corneas to become less sensitive. Shingles is most common in people over the age of 50.

Iridocorneal endothelial syndrome

(also known as ICE)

Iridocorneal endothelial syndrome is most common in women aged between 30 and 50. The main symptoms include alteration in the iris (the coloured area of the eye), irritation of the cornea and glaucoma; the syndrome is often only present in one eye. ICE comprises of three conditions that are very closely linked, which are iris nevus, Chandler’s syndrome and essential iris atrophy (degeneration). The major link between these conditions is that the endothelial cells move from cornea to the iris. ICE causes vision distortion, swelling of the cornea and pupil distortion. It is not known what causes ICE.

Keratoconus

Keratoconus is a rare condition which results in the cornea changing shape, becoming thinner and weaker. It is a progressive condition commonly affecting young people. Keratoconus is one of the most widespread reasons for cornea transplants in people under the age of 30. In many cases the condition is mild and can be controlled by wearing glasses or contact lenses. However, it can develop into a serious condition and a corneal transplant may be required. Keratoconus causes vision to become blurred and distorted as a result of the shape of the cornea changing, which reduces the power of the cornea to refract light rays. Keratoconus often has an impact on both eyes.

There are various possible causes of keratoconus, including injury to the eye, an inherited abnormality in the cornea and other eye and medical conditions, including retinitis pigmentosa, Down’s syndrome and Ehlers-Danlos syndrome.

Keratoconus can make wearing contact lenses difficult because the shape of the cornea is not standard, so it is imperative to wear well-fitting lenses to prevent damage to the eyes.

Lattice dystrophy

Lattice dystrophy causes amyloid deposits to collect in the stroma, forming a lattice shape. Initially the deposits look like clear dots, but as the condition progresses the lattice becomes opaque and this causes cloudiness in the cornea which can restrict vision. For some the deposits can collect under the epithelium (the outer layer of the cornea) and cause erosion, changing the shape of the cornea and exposing the nerves. To ease pain eye drops and ointments may be prescribed and pain usually subsides within 3 days. If the epithelium is scarred a corneal transplant may be required. Lattice dystrophy is most common in children aged between 2 and 7.

Map-dot fingerprint dystrophy

This condition is caused by abnormal development of the basement membrane of the epithelium. This prevents the epithelial cells from sticking to the lining, causing erosions which can change the shape of the cornea and cause blurred vision and pain (due to the nerves becoming exposed).

Map-dot fingerprint dystrophy can affect people of all ages, but it is most common in people aged between 40 and 70 and the condition tends to affect both eyes. The condition is named after the appearance of the damaged epithelium when examined during an eye test. In many cases people are not aware they have the condition because it does not always cause symptoms.

Ocular herpes

Ccular herpes is a viral infection brought on by the herpes simplex virus. Once you have been infected with the virus it is likely that you will experience flare-ups of symptoms, which include the development of a tender wound on the eyelid and swelling of the cornea. Anti-viral treatment is usually administered to try and prevent the virus from spreading. If the virus spreads further into the cornea this can cause a serious infection known as stromal keratitis, which prompts the immune system to start attacking stroma cells. Stromal keratitis is difficult to treat and it can be very severe, contributing to loss of sight. In most cases ocular herpes can be controlled effectively.

Pterygium

A pterygium is an abnormal growth on the cornea, which presents itself as a triangular pink growth. Researchers are unaware of what the cause of is, but it is believed that there is a link between the growths and exposure to sunlight. Pterygia is more frequent in people who live in warm and hot climates and is most commonly found in those aged between 20 and 40. In most cases pterygia is not a problem, although some people may want to have them taken out for cosmetic reasons; however, surgery is usually not recommended.

Stevens-Johnson syndrome (SJS)

Stevens-Johnson syndrome (also known as erythema multiforme major) is a condition that affects the skin and eyes. The most common symptom of SJS is painful lesions on the skin, in addition to the moist membranes in the mouth, eyelids, genitals and throat. SJS can cause severe conjunctivitis, blisters and erosions on the cornea, and, in some extreme cases, loss of sight. SJS is much more common in men than women and it tends to affect young adults and children. The exact cause is unknown, though scientists believe it may be a result of an adverse reaction to mediation. Treatments for symptoms caused by SJS include artificial tear drops, antibiotics and corticosteroids.

Cornea transplant

A cornea transplant is a procedure that involves removing a damaged cornea from an individual and replacing it with a healthy one. The healthy cornea is taken from another person (who has died) and implanted into the individual via a surgical procedure. Cornea transplants are made possible by people agreeing to donate their organs in the event of them passing away, and either the individual concerned or their family must give permission for their organs to be used before a transplant can be carried out. All donor corneas undergo stringent checks for infection before they are used.

Around 50% of cornea transplants are carried out as day cases and 50% of people are advised to stay overnight. Some transplants are carried out under general anaesthetic and some are done under local anaesthetic. Recovery times vary according to the type of procedure you have.

Why would I need a cornea transplant?

You may need a cornea transplant if your cornea is severely damaged, about which there are various reasons why this could happen, including:

Health conditions, including keratoconus and Fuchs’ endothelial dystrophy.
Recurrent infections, which do not respond to antibiotics (this is rare).
Perforation (a very small tear) of the cornea.

The aims of a cornea transplant are to ease pain, improve sight and prevent any further damage.

What does the procedure involve?

Recent developments in science and research mean there are various options for transplant procedures. In the past the only way to carry out the procedure was to remove the entire cornea; it is now possible to transplant layers of the cornea rather than the full thickness.

Penetrating keratoplasty

This is a procedure which involves removing the full thickness of the cornea and can be done under local or general anaesthetic. The central section of the cornea is removed and replaced with healthy cornea tissue from another person. The new cornea is stitched into place using very small stitches to form a star shape. The stitches remain in place for up to a year and may be visible, but will only be very faint. The procedure usually takes between 1 and 2 hours. Success rates vary according to the reason why the transplant was needed. The cornea can survive for more than 10 years in 90 percent of cases if the source of damage is keratoconus (when the cornea changes shape), but rates are lower, usually around 5 years, if damage is caused by infection or the formation of an ulcer in the cornea.

Outer cornea treatments

There are three methods that can be used to repair damage to the outer layers of the cornea. These are:

Laser eye surgery
laser eye surgery involves using an instrument called an excimer laser to reshape the cornea to correct sight problems, such as short-sightedness, long-sightedness and astigmatism.
Automated lamellar keratoplasty
this procedure is used to transplant the outer layer of the cornea. Recovery time is generally quick for this procedure because the middle and inner layers are not affected.
Deep anterior lamellar keratoplasty
this procedure can be used when the outer layer of the cornea is healthy but the middle section (known as the stroma) is damaged or abnormal. The procedure involves removing the diseased cornea and replacing it with healthy donor tissue. The donor tissue rests on the individual’s original corneal lining. Recovery time is usually longer but success rates are high.

Inner cornea treatment - Endothelial keratoplasty

This is a relatively new procedure and is used when the cornea has become waterlogged as a result of the endothelial cells (the deepest layer of the cornea) not working properly. This procedure involves removing the deepest layer of the cornea and the tissue is then replaced with healthy donor tissue, which is held in place by an air bubble. The air bubble remains in place until the tissue has successfully bonded with the individual’s own cornea. Endothelial keratoplasty is usually carried out under general anaesthetic. The outer layers of the cornea are not affected and this means that sight usually recovers very quickly. There are two specific methods used in endothelial keratoplasty these are called Descemet’s stripping endothelial keratoplasty and Descemet’s stripping automated endothelial keratoplasty.

Are there any risks involved?

As with all surgical procedures there are risks involved. The risks are fairly high for cornea transplant procedures, so surgery is usually regarded as a last resort after other treatments have failed.

Possible complications of cornea transplant procedures include:

Rejection
there is a risk of the body rejecting the donor organ, which is fairly common and occurs in around 20% of cases. The body mistakes the cornea for a harmful threat and attacks it. Treatment can usually be very successful for rejection, provided that it is administered early. Symptoms to look out for include clouding of the cornea, blurred vision, red eye and inflammation of the middle layer of the eye (this is called uveitis).
Infections.
Heightened sensitivity to light (known as photophobia).
Pain and irritation in the eye.
Blurred vision.
Glaucoma.
Surgical wounds.
Swelling in the eye (known as oedema).
Retinal detachment (when the retina comes loose).

There is currently a shortage of donor corneas in the UK and the Organ Donor Register is appealing for more people to agree to offer their organs.