Deep Anterior Lamellar Keratoplasty (DALK)

The cornea consists of 3 layers:

• On the surface is the epithelium, which protects us from external aggression, has a thickness of 50 µm and sits on Bowman’s membrane.
• The corneal stroma consists of collagen fibres and has an average thickness of 550 µm. It is situated between Bowman’s membrane and Descemet’s membrane, between the epithelium and the endothelium. If the corneal stroma is no longer transparent, light will find it more difficult to enter and your vision will therefore be impaired.
• Inside is the endothelium, consisting of just one cell layer which sits on Descemet’s membrane. The function of the endothelium is to draw out fluid from the stroma and discharge it to the anterior chamber. This is the space between the cornea and the iris. This can be compared with the mechanism of a water pump. Once damaged, this cell layer cannot be repaired.

Indications for DALK

There are various conditions that must be met before a corneal transplant can be considered. The most common indications are:

• abnormalities of the anterior part of the cornea (epithelium, Bowman’s membrane, but mainly stroma) with a normal layer of endothelium cells: corneal dystrophies
• very pronounced keratoconus: progressive malformation of the cornea preventing regular focusing of light on the retina
• corneal scars: post-trauma, post-infection (e. g. herpetic keratitis, infection caused by bacteria, burns)

In the last 50 years penetrating keratoplasty (PKP) or the replacement of the full thickness of the cornea by donor tissue, was the standard treatment for patients with corneal disorders. Although the anatomical results are outstanding, the visual results in terms of speed, quality and predictability are less favourable. A typical patient undergoing a corneal transplant can continue to suffer from impaired vision for 2 years. It is very difficult to predict the final curvature of the cornea. Hence, in most cases, glasses or contact lenses need to be worn after the operation. The stitches are only removed after a long period of time, and rupture of the wound due to an accident is always a major risk. Patients with bilateral disorders often have to wait a long time until the first treated eye is healed, before their second eye can be treated.

In recent years cornea specialists have developed techniques to replace just the diseased layer of the cornea, instead of the full thickness: these are known as lamellar keratoplasty techniques.

If the front part of the cornea is the reason for poor sight, such as with keratoconus or corneal dystrophy, only the epithelium and the stroma are replaced (the largest part of the cornea). This is referred to as Deep Anterior Lamellar Keratoplasty (DALK). Descemet’s membrane and the endothelium of the patient remain intact and form the surface support for the donor tissue. This technique ensures that the healing process is faster and the refractive result more predictable: the patient has a better chance of improved sight and the eye is stronger than before.

DALK will increasingly replace PKP in the future.

More about DALK

Advantages
Possible risks
The operation
Preparing for an operation