The cornea , including it’s anatomy, function and physical properties are discussed elsewhere on this website.
Due to the specialized nature and function of the cornea, corneal pathology will have huge impact on the quality of vision a person perceives. For the purpose of discussing corneal transplant, this pathology leading to a transplant my be categorized into three broad categories:
- Corneal opacity
- Thinning of the cornea
- Failure of the maintenance of corneal clarity
An example of each of the above is listed below:
- Corneal scarring : Injuries to the central cornea may cause permanent scarring within the field of vision. Virus infections with agents such as Herpes Simplex and Herpes Zoster infections are also leading causes for corneal scarring. Likewise, a corneal abscess secondary to contact lens wear may have the same impact on vision. Depending on the depth of involvement of such a scar, it might be possible to perform a transplant of the superficial layers only, leaving the internal layers intact.
- Keratoconus and other ectatic corneal degenerations: This condition is discussed elsewhere on this website.
Corneal endothelial conditions : The cornea consists of 5 layers, of which the epithelium is the most superficial layer, while the endothelium forms the internal layer of the cornea. Pathology of the outer epithelium layer is often characterized by erosions which is of a transient nature and usually not clinically important. Dystrophy of the monolayer of endothelial cells, on the other hand, may cause corneal decompensation with severe impact on vision. The most frequent conditions affecting this layer of cells are Fuch’s endothelial dystrophy and pseudophakic bullous keratopathy. The latter condition is seen from time to time in patients who underwent cataract surgery during the 1980’s or ealier, and had a lens placement in the anterior chamber which caused the corneal endothelium to decompensate. With the advent of modern technology, it is now possible to perform a transplantation of the internal part of the cornea only through the DSAEK (Descemet Stripping Automated Endothelial Keratoplasty) procedure.
Four techniques of corneal transplant are in frequent use today, the application thereof depending on the layer of the cornea which is affected and has to be replaced. These techniques are:
This procedure is the most established technique, and has been available for a number of years. This implies the removal of the entire central cornea, with the replacement thereof by donor tissue. This procedure is indicated in advanced cases of keratoconus, or when the scarring or disease process involves the entire thickness of the corneal stroma.
It is, however, possible to only replace the affected layer of the cornea, with preservation of the recipient’s own tissue to minimize complications. These transplant procedures are termed “lamellar corneal transplants” and are the latest additions to corneal transplant surgery.
- Anterior lamellar corneal transplant (ALTK): Through this technique, only the superficial part of the corneal stroma is removed and replaced by a similar donor section. The advantages of this procedure include the fact that the surgery remains superficial with the result that the host’s endothelial cell layer is preserved. A smaller bulk of tissue is transplanted, which reduces the antigenic load, and hence the chances of rejection. This procedure is indicated if the superficial part of the cornea is the only part affected, thus negating the need for a penetrating corneal transplant.It is, however, possible to only replace the affected layer of the cornea, with preservation of the recipient’s own tissue to minimize complications. These transplant procedures are termed “lamellar corneal transplants” and are the latest additions to corneal transplant surgery.
- Deep lamellar endothelial keratoplasty: This technique is very similar to the ALTK, except that the whole corneal stroma is replaced (only the corneal endothelium and the Descemet’s membrane is left in situ). This procedure is indicated if the whole cornea is affected except for the corneal endothelium and Descemet’s membrane.
- Descemet’s Stripping Automated Endothelial Keratoplasty (DSAEK): It is now possible to replace the corneal endothelium along with Descemet’s membrane and a thin layer of the internal stroma. This procedure is significantly less invasive as opposed to a penetrating transplant, and the recovery is usually within a short span of time. This method is indicated in patients with corneal endothelial problems such as Fuch’s endothelial dystrophy, post-surgical corneal oedema and corneal regrafts.
Who are candidates for a corneal transplant?
People become eligible for a corneal transplant only if their vision cannot be improved by wearing hard contact lenses or spectacles.
Corneal transplant surgery is believed to be one of the most successful types of transplant surgery, and the techniques are improving constantly. At Optimed Eye and Laser Clinic we are fortunate to have some of the most advanced equipment to perform the latest techniques.
Admission to the Optimed Eye and Laser Clinic occurs on the day of the scheduled surgery, and although the surgery is done under general anaesthetic, it can be done on an outpatient basis as a rule. It is therefore wise to arrange for transport to and from the clinic.
It is normal for the eye to feel scratchy and irritated for the first few days following surgery. If severe pain and nausea is experienced, our consulting rooms should be contacted immediately. It is important to also contact us should any of the following symptoms be experienced:
- sudden reduction or loss of vision
- persistent discomfort and tearing
- sudden light sensitivity
You will need to:
- use eye drops as prescribed, and rest for a day or two
- refrain from rubbing or applying pressure to the eye
- use over-the-counter analgesics if necessary
- wear an eye shield or sunglasses as advised
- plan on taking leave of absence from work for approximately 2 weeks (Dr Potgieter will provide you with a medical sertificate for the period)
- attend all your follow up appointments
The recovery period following a corneal transplant can be as long as one year, depending on the type of transplant. Over this period, frequent follow-up visits are necessary to ascertain proper healing of the graft. It is accustomary to remove the corneal sutures in a staged fashion, so that by one year post-operatively the final sutures are removed. Another period of 6 months is then allowed for the cornea to stabilize.
The cornea is usually stable 6 months after the removal of the final sutures. At this point, the residual refractive component can be addressed if required by means of the applicable refractive surgery technique.
Limbal stem cell transplant
The limbal stem cells are specialized cells located at the periphery of the cornea. They are responsible for the regeneration and renewal of the corneal epithelium, and also prevent conjunctival epithelial growth onto the cornea.
A limbal stem cell transplant is indicated in cases where there is an unfavorable environment for limbal stem cell support like in the case of some systemic diseases, chemical and thermal injuries, ultra violet or ionizing radiation, contact lens wear and multiple ocular surgeries.
Limbal stem cells can be harvested from the conjunctiva / cornea of the fellow eye (autograft), a relative’s eye (allograft) or from a donor eye (allograft).