Cornea


Corneal Transplant

What is a corneal transplant?

The cornea is the dome-shaped window that forms the front surface of the eye. It is made up of several layers, all of which are transparent. Diseases of the cornea may affect one or more of these layers.

Corneal transplant surgery, also known as corneal graft surgery and keratoplasty, replaces an abnormal cornea with a cornea from a donor eye in order to restore vision.

Who needs a corneal transplant?

Many people with a cloudy cornea from scarring after infection or injury will benefit from corneal transplant surgery. Some inherited or degenerative conditions, like  Fuch’s endothelial dystrophy, may lead to swelling of the cornea, which requires corneal transplant surgery when it affects the vision or causes pain. In keratoconus the cornea becomes thinned and distorted, resulting in blurring of vision. In about 15% of cases, when other treatments such as contact lenses no longer help, corneal transplantation is necessary.

Unlike most other organ transplants, if a corneal transplant fails it can be repeated, although the success rate of repeat transplants may be lower than first time transplants.

How is corneal transplant surgery performed?

Corneal transplant surgery may be performed under general or local anaesthetic. It generally takes between one and two hours and is day surgery, not requiring an overnight hospital stay.

There are several types of corneal transplants performed by Eye Doctors. In about half of corneal transplant surgery all corneal layers are affected, requiring a standard, full thickness transplant or ‘penetrating keratoplasty’ (PK). This includes surgery for some corneal scars and some keratoconus, which is the most common reason for corneal transplant surgery in New Zealand. The central 7-8mm of the damaged cornea is removed and replaced with a similar sized piece of clear donor cornea, which is stitched in place with fine nylon microsutures.

In other cases, particularly the less advanced cases of keratoconus, a partial thickness ‘deep anterior lamellar keratoplasty’ (DALK) may be suitable. In this surgery the innermost corneal layer, or endothelium, is healthy, so is not replaced. This reduces the risk of corneal transplant rejection and failure in the long term.

Other corneal disorders only require replacement of the innermost corneal layer, or endothelium. In Fuchs’ dystrophy and bullous keratopathy only this thin layer needs to be replaced, in a procedure known as ‘descemets stripping automated endothelial keratoplasty’ (DSAEK). This is done through a small keyhole incision at the edge of the cornea and has the advantages of a faster healing time and no/minimal stitches on the eye.

Eye Doctors are experienced in medical treatment of corneal diseases and in the latest surgical techniques for corneal transplantation, including partial thickness corneal transplantation. Our corneal surgeon can discuss the different types of corneal transplant with you and which type of surgery is most suitable.

Is corneal transplant surgery safe?

Corneal transplantation is quite a major surgery for the eye and should not be undertaken lightly. The healing period can be over a year for full-thickness corneal transplant and while the final vision can be as good as 20/20 (6/6), this is certainly not guaranteed.

Significant complications during the surgery are rare, but there are some potentially serious risks, such as transplant rejection, which can lead to transplant failure if not treated promptly. Our corneal surgeon can advise you of the pros and cons of corneal transplant surgery.


Keratoconus

What is keratoconus?

The cornea is the transparent dome-shaped window on the surface of the eye, overlying the coloured iris. Its smooth round surface is important for maintaining clear vision. In keratoconus the cornea becomes thin and distorted, eventually protruding forwards in a cone-like shape. It typically affects both eyes, but can often be quite asymmetric.


Why does keratoconus develop?

The causes of keratoconus are not very well understood. However there is a genetic tendency, so it can sometimes run in families. There is also an association with allergies and most people with keratoconus have itchy eyes and rub their eyes to some degree. Over several years the pressure on the eye from rubbing may contribute to distortion of the cornea.

Who gets keratoconus?

Keratoconus occurs in young people, often starting in the teens, or even younger. It usually progresses slowly, and then stabilizes by the thirties. It affects males and females in all racial groups, although in New Zealand it is most common in the Maori, Pacific Island and Indian populations.

What are the main symptoms of keratoconus?

Keratoconus causes blurring and distortion of vision in one or both eyes. It often gets slowly worse over time, but occasionally causes quite a sudden deterioration in vision. People with keratoconus often have associated allergic conjunctivitis, which causes itchy eyes and eye rubbing.

What treatments can help with keratoconus?

There are two main aims in treating keratoconus; improving vision and preventing progression of the disease. 

In the early stages of keratoconus, glasses or soft contact lenses may help correct blurred vision. As the cornea becomes more distorted only hard contact lenses are able to improve vision. About 15% of people with keratoconus progress to the stage where corneal transplant surgery is required.Traditionally full-thickness corneal transplant surgery has been necessary but in some cases of keratoconus it is now possible to perform a partial transplant, which has advantages in long term transplant survival.

In recent years preventing progression of keratoconus has become a priority for people with mild or moderate keratoconus. Treating allergic eye disease and avoiding eye rubbing may be of some benefit. 

Corneal collagen cross linking (CXL) is a treatment designed to stabilise keratoconus. It uses a combination of ultraviolet light and vitamin B2 to stiffen the cornea, slowing or halting keratoconus progression. It is effective in more than 90% of cases and at least 50% of people also have some improvement, with better vision and improved contact lens tolerance. CXL may reduce the need for corneal transplant surgery, by preventing keratoconus from progressing to more advanced disease. Our corneal surgeon can advise which treatment is most suitable for you.

You can find out more information from the following websites:

www.nkcf.org


Collagen Cross Linking for Keratoconus

What is Collagen Cross Linking?

Corneal collagen cross linking (CXL) is an effective new treatment for keratoconus and other forms of corneal ectasia. A combination of ultraviolet light and vitamin B2 causes corneal collagen fibres to bond more tightly to each other. This stiffens the cornea, making it less prone to deformation and slows or halts the progression of corneal ectasia.

Why consider this treatment?

Keratoconus can cause significant loss of vision. By stabilising the cornea in the early or moderate stages of the disease, further vision loss can be prevented. About 50% of people also have some improvement, with flattening of the cornea, better unaided and corrected vision and improved contact lens tolerance. CXL also reduces the need for corneal transplant surgery, by preventing keratoconus from progressing to more advanced disease.

Who should have this treatment?

Collagen cross linking is suitable for adults and teenagers with mild or moderate keratoconus that has shown definite progression over a period of at least three months. This includes at least one dioptre of corneal steepening or refractive change.  A clear cornea with a minimum thickness of 400 microns is required.

How is cross linking performed?

CXL is performed by Dr Penny McAllum in the Eye Doctors clinic and at Ascot Hospital. One eye of a patient is treated at a time. After local anaesthetic eyedrops are instilled, the central corneal epithelium is removed and the surface of the eye is soaked in Riboflavin (Vitamin B2) eyedrops for half an hour. The cornea is then exposed to a specially calibrated ultraviolet light for half an hour, with regular checks to ensure the cornea is not becoming too thin. A bandage contact lens is placed and left on for several days while the eye heals. Antibiotic and anti-inflammatory eyedrops are used for up to four weeks and painkillers are prescribed for use as necessary in the first two-three days. About five follow-up visits are required in the three months following the treatment.