Corneal disease
Surgical treatment
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| A transplanted cornea. The donor cornea has been secured with a 'single continuous' suture. |
Some corneal diseases can only be treated surgically.
Types of corneal surgery
There are three principal types of corneal surgery:
- Phototherapeutic keratectomy
- Penetrating keratoplasty, in which the whole cornea is transplanted
- Lamellar keratoplasty, where selected layers of the cornea are transplanted
Phototherapeutic keratectomy
The excimer laser can be used to smooth and reshape a diseased cornea.
The commonest indications are:
- Recurrent erosion sydrome
- Superficial scarring
Penetrating keratoplasty
Penetrating or full thickness corneal transplantation. Courtesy Alcon.
Penetrating surgery is performed when the whole thickness of the cornea is affected by disease. The most common condition treated in this fashion is keratoconus, or 'conical cornea'.
Lamellar keratoplasty
Individual layers of the cornea can be transplanted. The commonest surgeries are:
- Anterior lamellar keratoplasty - replacement of the corneal stroma
- Posterior lamellar keratoplasty - replacement of the corneal endothelium
Anterior lamellar keratoplasty
Anterior lamellar surgery can be performed when disease is isolated in the corneal stroma.
Advantages of this technique include:
- Only the diseased part of the cornea is replaced
- The likelihood of graft rejection is lower
There are however several disadvantages:
- The surgery is much more technically difficult
- Intraoperative complications are common and often require the surgeon to proceed with a full thickness transplant
- The visual results are probably not as good
Posterior lamellar transplantation
Many corneal diseases affect just the endothelial cell layer. At present it is not possible to replace just this single cell layer. We can however transplant the endothelium attached to Descemet's membrane together with a thin layer of posterior stroma. The most common operation of this type is known as Descemet's Stripping Endothelial Keratoplasy or DSEK.
DSEK
In DSEK (Descemets Stripping Endothelial Keratoplasty) diseased endothelium is stripped from the back surface of the patient's cornea and a donor cornea disc is placed against this 'raw' surface. A bubble of air is used to hold the grafted tissue in place for the first 24 hours until healing begins. No sutures are required. Patients need to lie flat on their back during the first 24 hours to allow the air bubble to keep the new graft in place.
The advantages of this technique are:
- The eye is structurally sound
- Recovery is quicker
- There is probably less likelihood of rejection
- The smooth front surface of the eye remains unaltered
The disadvantages are:
- Surgery is more technically difficult and expensive
- Slightly higher failure rates
Donor corneas
All corneal transplantation uses human tissue from individuals who have donated their organs at death.
Risks of corneal transplantation
Corneal transplantation is a major undertaking. Risks include:
- Infection at the time of surgery
- Dislocation of the donor button. This is a unique complication of posterior lamellar surgery and usually occurs within the first 48 hours. Most dislocated corneas can be refloated.
- Graft failure. Occasionally a transplanted cornea fails to survive the transplant process.
- Rejection. The host eye can reject the transplanted cornea. The chances of this depend on many factors including the underlying eye problem, the type of surgery and the number of grafts previously performed.
- Weakness of the eye. The eye is never as robust following penetrating surgery. A blow could rupture the eye and lead to blindness. Contact sports are not permitted after penetrating keratoplasty.
- Astigmatism. The surface of a transplanted cornea is always somewhat irregular. Many patients require futher surgery or a rigid contact lens to obtain good vision.
- Scar tissue. This can occur in the host (patient) cornea, the donor cornea and between the two corneas.
- Cataract formation
- Recurrence of the disease being treated in the transplanted cornea
- Transmission of disease from donor tissue. This is unbelievebly rare. All donors are screened for diseases such as hepatitis and HIV/AIDS. It is estimated that at present rates of tranplantation in New Zealand one person will develop an infection from donor tissue every 200 years.
- Rare complications such as retinal swelling or detachment, glaucoma and chronic inflammation.
- Very rare complications include loss of vision.
Further information
For more information on the practical aspects of having corneal surgery see Having Corneal Surgery