Pre-Operation Information - Corneal Transplant (Corneal Graft) Surgery

What is the Cornea?

The cornea is the clear “window” of the eye, and is approximately 0.5 mm thick and 12 mm across.  It is positioned in front of the fluid filled anterior chamber of the eye and the coloured iris.  It is like the lens of a camera – any opacity or distortion results in a poorly focused image.

The cornea has three layers:

1.The thin surface “skin” (or epithelium)

2.The thicker central layer (or stroma)

3.The single layer of cells on the back surface (or endothelium) – this layer of cells is not replaced through life and cannot regenerate if damaged or diseased.

All of these layers must be clear and smooth for the cornea to work as a window.  The cells of the back surface layer (endothelium) pump fluid out of the cornea to maintain its thickness at about 0.5 mm – if this layer stops functioning normally the corneal thickness increases and starts to become cloudy (corneal failure or decompensation).  With continued swelling the cornea becomes waterlogged resulting in blistering of the “skin” (epithelium) of the cornea (called bullous keratopathy) leading to pain in addition to blindness.

What can go wrong with the cornea?

All the layers can be affected individually or in combination.  None of these problems are very frequent within the population.

More commonly:

1.The central layer (stroma) may become scarred (as a result of injury or infection) or irregular in shape as a result of conditions that are probably genetically determined such as keratoconus and keratoglobus or due to dystrophies such as lattice, granular and macular dystrophy.

2.The back surface layer (endothelium) may become inadequate to maintain its pumping action (corneal failure or decompensation) as a result of genetically determined conditions such as Fuch’s dystrophy or injury from trauma or surgery.

Less commonly:

1.The cornea may develop a hole (perforation) in the central layer (stroma) as a result of inflammation or infection.  If this is not treated quickly the eye usually becomes blind.

2.The cornea may become opaque due to damage to the “skin” (epithelium) causing growth of tissue around the edge of the cornea (limbus) usually as a result of severe inflammation or a chemical injury.

Why have a corneal transplant (graft)?

To replace a damaged cornea with a donated cornea is the only available treatment for severely damaged corneas (apart from artificial corneal transplants (keratoprosthesis) which are only for very badly damaged eyes when conventional graft surgery is known to fail or to have already failed).

Corneal transplantation is only worth doing when the inside of the eye (retina and optic nerve) and the parts of the brain that deal with vision (visual pathways and occipital cortex) are still functioning adequately.  Conditions that may have damaged the inside of the eye are glaucoma, optic nerve disease, retinal detachment, severe inflammation or infection inside the eye.  Conditions that may have affected the visual pathways and cortex are stroke, trauma, infection, inflammation or tumours.

An eye with potential vision can always detect light well even when the cornea is completely opaque.

What type of corneal transplant (graft) should I have?

There are two principal types:

1.Partial thickness (Lamellar keratoplasty)

2.Full thickness (Penetrating keratoplasty)

Lamellar (partial thickness) corneal grafts have been less frequently used in recent years but are increasing in popularity due to a possibly reduced risk of rejection and late graft failure, as well as better techniques for performing the surgery.

Lamellar grafts can be used to replace the front surface of the cornea including epithelium and stroma (Deep anterior lamellar keratoplasty, DALK) or the back surface or endothelium (Endothelial keratoplasty, known by many acronyms PLK, DSEK, DMEK, DSAEK, and others) leaving in place any healthy tissue the diseased cornea may have left.
Lamellar grafts are not suitable for all corneas.  Suitability is determined by the extent of disease or damage.

The disadvantage of lamellar surgery is that it can be technically more difficult and may need to be converted to full thickness surgery during the procedure if complications occur.  The final visual outcome from a successful lamellar graft is generally not quite as good as a successful penetrating graft.

Penetrating (full thickness) corneal grafts have been the most widely carried out for all types of corneal disease for 45 years.  However this type of graft is only mandatory if all the layers of the cornea are diseased or damaged.

For epithelial or stromal disease it is carried out because it is easier to replace the whole cornea rather than a layer and because the vision is possibly better after a full thickness graft.  The disadvantage is that it is the transplanted graft endothelium that is the principal stimulus for rejection which is the commonest complication of this type of graft (about 20% for low risk cases) and leads to graft failure in some.  Also the donor endothelium has a limited life-span. 

In general I recommend the procedure that best suits the needs of the patient, and the eye and the procedure that is likely to give the best vision with the least risks in the short and long term.

Why not to have a corneal transplant (graft)?

1.If you are not prepared for a long recovery period and numerous follow up visits.

a.A corneal graft operation is a major procedure for the eye and the recovery period for good vision is very prolonged (18-24 months), although some patients might notice an improvement within a few days of surgery.

b.A minimum of 10 post operative visits is needed and the average is higher.  Most patients will need lifelong follow up with an ophthalmologist.

c.The likelihood of good vision without any form of correction (spectacles, contact lenses or refractive surgery) is very low.

i.    15% of patients need contact lenses (usually rigid gas permeable contact lenses) for best vision

ii.   10% require surgery for astigmatism

2.If your other eye is healthy you should think very carefully about having a corneal graft as the quality of vision will seldom be as good in the grafted eye.

3.If you are forgetful about your treatment

a.You must be able to take eye drops for a minimum of 6 months, but usually up to 2 years or more.

b.Forgetting to take medication is a frequent cause of graft failure.

Where does the corneal transplant come from and how safe is it?

The donated cornea is human tissue that comes from a human donor who has died.

Unlike other whole organ transplants the cornea can be removed several hours (up to 12 hours) after death and is only rarely harvested from a “brain dead” donor.  Retrievals of donor material are only done on those patients who are medically suitable and whose families have generously agreed to donation within 12 hours after the death of the patient.  There is no money paid to the donor family and any information regarding the donation and transplantation is kept private under the Privacy of Information Act in NSW. 

Donor corneas are provided by the Lions NSW Eye Bank.  The Lions NSW Eye Bank is governed by the exacting standards of the Therapeutic Goods Administration (TGA) that controls all pharmaceuticals and prostheses in Australia.

All donors are screened for medical conditions that would pose a potentially health threatening risk to a recipient, or the risk of surgery.  This is based on the evidence of a high likelihood that the recipient may be put at risk of a transmissible disease; particularly virus or other biological materials.  Donors are also screened on the basis of risk factors associated with Creuztfeld-Jacob Disease, diseases of unknown aetiology, systemic infections, systemic malignancies and ocular disorders.  Blood from the donor is screened for Hepatitis B and C and HIV, risk factors for these diseases are also screened. 

Donor transplants are not released for use until the donors have been shown to have:

1.No antibodies for hepatitis or HIV (the virus that causes AIDS) (there is a very small risk of donors having these diseases but not having antibodies, but no donor has ever transmitted HIV via a corneal graft.

2.No medical record of an undiagnosed neurological disease or degenerative neurological disorder such as Parkinsons disease or Creuztfeld-Jacob disease (there have been only 3 reports in which recipients of corneal donor material MAY have developed CJD from corneal donors despite the 30,000 grafts a year carried out in the UK and USA alone)

3.Donor material is assessed for quality including clarity, and the health of the posterior layer (endothelium) by specula microscopy cell counts.  Providing the endothelium is in good condition the age of the donor has been shown to be irrelevant (i.e.  an 80 year old donor can provide tissue that is expected to last as well as that from a 30 year old donor).  Tissue will only be released for transplantation if it is deemed suitable by the Eye Bank Laboratory staff.  There is a limbal swab done for Microbiology studies, and all corneas that do not meet criteria are discarded. 

The donor material can be stored in purpose designed medium (Optisol) for about 7 days and must be used within this period. 

Tissue matching: there is little evidence this is of benefit for low risk corneal transplants.  Patients at high risk of rejection may derive some benefit from tissue matched donor cornea.

Approximately 350 corneas are transplanted every year in NSW.

There are currently more patients needing transplants than donor corneas available. 

A system of scheduling of patients is now in place and all new patients that are placed on the wait list for a graft will be given a date for their graft surgery.  The average wait time for a corneal graft is 6 months.  However if the patient is deemed as needing a cornea sooner than that, then they are given a priority rating.  Usually this means that a cornea should be provided within a matter of weeks.   A priority rating is based on the visual acuity of the patient as well as social factors, such as not functioning on a day to day basis, in danger of losing their job, or a high degree of pain associated with the eye condition.

Private patients are charged a fee for the service that is claimable from their health fund.  The area health service covers the cost of the tissue for public patients.