Deep anterior lamellar keratoplasty (DALK) surgery can be used to correct any pathology involving the anterior cornea, that is the Bowman’s layer, stroma, and epithelium. The procedure will remove and replace either parts or all of the corneal stroma while leaving the endothelium intact. Keratoconus patients and those with corneal scarring are the best candidates for DALK. However, DALk can only be performed if the patient has a functioning endothelium.
DALK is a subcategory of lamellar keratoplasty where the corneal stroma is selectively removed and replaced. It is a partial thickness corneal transplantation with the advantage of reduced endothelial graft rejection. The procedure also minimizes surgical trauma and preserves the host endothelium, unlike penetrating keratoplasty (PK). DALK has fewer intraoperative and postoperative complications. Besides, the process of donor selection is less rigid.
Other patients who can benefit from DALK include those with:
- Stromal scars
- Stromal opacity
- Pellucid marginal degeneration
- Active corneal ulcers and perforations
- Ectasia arising from a LASIK procedure
- Stromal dystrophies such as lattice, macular and granular
However, DALK is not suitable for those diseases that affect the endothelium, such as:
- Endothelial dysfunction
- Iridocorneal endothelial syndrome
- Posterior polymorphous dystrophy
- Pseudophakic bullous keratopathy
- Deep scars that involve the Descemet membrane (DM) such as acute hydrops
- Fuchs’ endothelial dystrophy (swollen cornea causes glare, halo, and reduction in visual acuity)
- Direct open dissection
- Dissection with hydrodelamination
- Closed dissection (Melles Technique)
- Dissection with Anwar’s big bubble technique
- Big bubble technique combined with femtosecond laser trephination
- Other modifications
Before the Procedure
The donor tissue is prepared in advance of surgery, following the laid down medical procedures. The donor should be aged two to 75 years with donor tissue preserved for a maximum of seven days. There are specifications concerning the thickness or thinness, diameter, and density of donor tissue. The surgeon may prepare the tissue just before the procedure or have an eye bank prepare it.
The patient will undergo several ophthalmic examinations as well as have their medical history taken.
Local or general anesthesia will be used to numb the eye or relax the patient. Many approaches exist for performing DALK, but the procedure consists of the following basic steps in which the surgeon:
- Uses a suction trephine to cut the anterior corneal surface
- Dissects the stromal layers using a rounded blade, and angled parallel to Descemet’s membrane
- Using a cannula injects air or fluid in between the Descemet's membrane and deep stroma to separate the layers
- Sutures in place the donor tissue after the DM’s removal
Previously, DALK presented with the risk of the DM’s rupture or perforation necessitating improvements in the technique. The following represents those improvements and types of DALK:
- Direct open dissection using a dissecting blade to make a partial trephination. The surgeon follows it up with a lamellar dissection. This method still exposes the DM to the risk of perforation
- Dissection with hydrodelamination uses an intrastromal fluid injection to achieve partial trephination and lamellar keratectomy. The surgeon uses a needle to inject saline into the stromal bed, causing the stroma to swell, thus separating the tissue. However, DM rupture may still occur
- Closed dissection (Melles Technique). Here, aqueous is exchanged with air. The surgeon then creates a stromal pocket (long and deep) across the cornea using a specially designed spatula. S/he further enlarges the pocket through a viscoelastic injection and sideway spatula movements. The surgeon enters the viscopocket using a suction trephine blade to excise the stroma. S/he then sutures in place a full-thickness donor button
- Dissection with Anwar’s big bubble technique where the surgeon trephines and dissects the cornea at a 60-80% depth. Using a needle or specially designed cannula, the surgeon injects air paracentrally to produce a big bubble that separates the DM from the stroma. The surgeon sutures in place either the same size or a 0.25 mm oversized donor after removing the donor DM
- Big bubble technique combined with femtosecond laser trephination where the surgeon dissects the anterior lamella using a femtosecond laser. The surgeon aims to reduce postoperative astigmatism, allow for earlier removal of the suture, and improve the strength of the wound
- Other modifications to the big bubble technique can be used in unusual cases such as descemetocele, healed hydrops, and a cornea containing 16 radial keratotomy incisions
Risks & Complications
Perforation and entry into the anterior chamber from the stroma are the most frequent DALK complications. The sharp instruments used are responsible for the perforations. The later improved techniques like viscoelastic dissection technique can prevent these perforations. Some of these perforations are self-healing, for example, in cases where the perforation occurs while the stroma still covers the DM. The perforations that occur during dissection can lead to DM detachment postoperatively. To manage the detachment, an air or gas/air mixture injection is administered into the anterior chamber after surgery. Other risks and complications may include stromal rejection and a fixed, dilated pupil (Urrets-Zavalia syndrome).
Aftercare & Recovery
The surgeon prescribes topical corticosteroids and antibiotics for the patient to self-administer postoperatively. The patient will be monitored for graft rejection, astigmatism, infection, inflammation, and problems involving sutures.
The first follow up visit is scheduled for the day after surgery then one week, one month, three months, and so on depending on patient recovery.
DALK improves higher-order aberrations, contrast sensitivity function, and the best-corrected visual acuity (BCVA). Several studies have shown comparable visual outcomes between DALK and PK, as well as between DALK and intralase-enabled keratoplasty. Another study showed that 90.9% of DALK patients attained a BCVA of 20/30 or better as the final outcome.