3 Deep Anterior Lamellar Keratoplasty
Summary
Anterior lamellar keratoplasty (ALK) refers to the transplantation of only the anterior layers of the cornea and can be done when the pathology involves only the anterior part of the stroma with healthy endothelium. It can be classified into superficial anterior lamellar keratoplasty (SALK) and deep anterior lamellar keratoplasty (DALK).
DALK refers to the procedure where all the layers of the cornea excluding the pre-Descemet’s layer (PDL), Descemet’s membrane (DM), and the endothelium are replaced. It is commonly performed in conditions like corneal ectasias, superficial and deep corneal scars not involving DM, and stromal dystrophies. The commonly performed technique is the Anwar’s big bubble technique. Various other techniques of DALK include manual dissection DALK, femtosecond laser assisted DALK, and intraoperative OCT assisted DALK. A new technique called Jacob’s modified technique of pre-Descemetic DALK has been devised for the treatment of acute hydrops. Surgery in the acute stage immediately after the occurrence of hydrops using this technique prevents stromal scarring during the healing process and also provides anatomical correction of ectasia and thinning. The procedure also simultaneously targets multiple pathologies that can be associated with advanced ectasia and results in topographic, pachymetric, biomechanical, visual, and structural improvement while allowing decreased contact lens dependence. It provides early and rapid visual rehabilitation, early anatomic rehabilitation, and optical correction by regaining corneal structure and transparency. It closes the Descemetic break while still maintaining transparency over the area of the break. As the host DM and endothelium are retained and scarring over the visual axis is avoided, it avoids the risks associated with a penetrating keratoplasty (PK) such as rejection and secondary graft failure.
3.1 Introduction
Corneal transplantation was first successfully done in the human eye in 1905 by an Austrian ophthalmologist Eduard Zirm. 1 Since then, PK has been allowed restoration of vision in many patients with corneal pathology. More recently, however, lamellar keratoplasty (LK) has become popular as a means of selective transplantation of corneal layers.
Anterior lamellar keratoplasty refers to the transplantation of only the anterior layers of the cornea and can be done when the pathology involves only the anterior part of the stroma. It is suitable in patients with healthy endothelium such as keratoconus or anterior corneal dystrophies. It can be classified into SALK and DALK. 2 , 3
3.2 Advantages of Anterior Lamellar Keratoplasty over Penetrating Keratoplasty
ALK has numerous advantages:
It allows a closed globe surgery and avoids complications that can be associated with open sky surgery such as intraoperative expulsive hemorrhage or postoperative endophthalmitis.
Retention of the host endothelium decreases the risk of rejection as well as failure secondary to long-term endothelial loss. Though stromal and epithelial rejections could still occur, these are generally milder and can be treated with topical steroids successfully with good recovery of clarity and function.
Unlike in PK, where it is vital to avoid sutures going close to the limbus, this is not as crucial in ALK, thus allowing the use of larger sized grafts.
Suture removal can be done earlier, thus reducing the risk of suture-related complications and providing faster visual rehabilitation.
ALK decreases the incidence of high postoperative astigmatism.
Topical steroids may be discontinued earlier, thus reducing steroid-induced complications like cataract/glaucoma.
It leads to stronger and a biomechanically more stable globe with less risk of posttraumatic wound rupture.
It allows the usage of a larger pool of donor graft as the quality of endothelium is no longer a concern.
The follow-up is easier and can be less intense.
DALK is preferable in dry and harsh environmental areas and in those with ocular surface disorders, both the situations lead to an increased risk of neovascularization of the cornea. A PK in a similar situation would lead to increased chances of rejection.
3.3 Techniques for Anterior Lamellar Keratoplasty
3.3.1 Superficial Anterior Lamellar Keratoplasty
SALK refers to transplantation of 30 to 50% of the anterior cornea.
Indications
Superficial corneal scars—postinfectious/posttraumatic/postphotorefractive keratectomy/postchemical injury scars.
Scarring secondary to trachoma.
Corneal degenerations like Salzmann nodular degeneration.
Epithelial and stromal dystrophies limited to anterior one-third of cornea.
Recurrent epithelial ingrowth after laser-assisted in situ keratomileusis (LASIK).
Limbal dermoid excision—eccentric SALK.
SALK can also be performed in various special ways:
Microkeratome-assisted ALK: An automated microkeratome is used to cut the donor and the recipient corneas. The anterior cut stroma of the donor graft is then placed on the host cornea and sutured. 4 , 5 , 6
Femtosecond laser-assisted SALK: The femtosecond laser is used to create the lamellar cuts in both the donor and the recipient corneas. 7
Excimer laser-assisted ALK: Here, a deep excimer laser ablation is done on the host cornea with a plano configuration followed by suturing of a donor lamellar button on the recipient bed.
3.3.2 Deep Anterior Lamellar Kratoplasty
DALK refers to the procedure where all the layers of the cornea excluding the PDL, DM, and the endothelium are replaced.
Indications
Corneal ectasias—keratoconus, pellucid marginal degeneration, and post-LASIK ectasia.
Superficial and deep corneal scars not involving DM.
Stromal dystrophies.
Mucopolysaccharidosis.
Therapeutic DALK.
Tectonic DALK for descemetocele.
Acute hydrops—primary stage with modifications in technique.
Contraindications
Corneal dystrophies involving the endothelium.
Deep scars involving the endothelium and overlying the pupillary axis.
Keratoconic patients with coexisting Fuchs endothelial dystrophy.
Cystinosis with endothelial involvement.
Infective keratitis with Descemetic/endothelial involvement.
Penetrating ocular trauma.
Surgical Technique
Anwar first proposed the most commonly used technique known as the “big bubble technique.” 8 , 9 , 10 The cornea is trephined to partial thickness up to a depth of 80%. A 26-gauge needle attached to an air-filled syringe is inserted into the stromal lamellae from the depth of the trephined groove and air is injected into the corneal stroma. This leads to the formation of type 1 bubble, which separates the PDL, DM, and the endothelium on one side from the overlying stroma on the other side. This big bubble is then expanded till the edge of the trephined groove. A small paracentesis may be created and a small bubble is injected into the anterior chamber to perform the big bubble—small bubble test. If the small bubble remains at the periphery of the anterior chamber, it indicates the creation of the big bubble, which is occupying space in the center of the anterior chamber. On the other hand, if the small bubble migrates to the center of the cornea, it indicates the absence of a big bubble. Once a big bubble has been confirmed by the small bubble test, superficial anterior keratectomy is done. This is followed by opening the big bubble space using a 15° blade and then using a curved Vannas scissor for cutting the remaining anterior stromal layers into quadrants, which are then excised along the trephined groove. The donor cornea from which the DM and the endothelium have been stripped is sutured over the recipient bed (▶Fig. 3.1).
Various other techniques for performing DALK include:
Fluid/viscoelastic dissection: For the separation of stroma from the underlying layers. 11 , 12
Manual dissection DALK: Anterior chamber is filled with an air bubble and the stroma is dissected layer by layer. The depth of the instrument in relation to the posterior corneal surface can be visualized using the Melles technique.
Femtosecond laser-assisted DALK: The femtosecond laser is used to create lamellar cuts in both the donor and the recipient corneas. It can also be used to create side cuts, which can be vertical or in shaped patterns such as mushroom-shaped or zigzag cuts. The better apposition obtained between the graft and the recipient with these shaped cuts makes it possible to decrease the number of corneal sutures used, thus allowing a decrease in induced astigmatism. However, the amount of astigmatism that is induced finally will also depend on the suturing technique.
Intraoperative optical coherence tomography (OCT)-assisted DALK: The intraoperative OCT (iOCT) can be used in various stages of surgery such as determining the depth of dissection of the initial groove, determining the depth at which the needle is passed into the deep stroma for creating a big bubble, confirming the formation of the big bubble, identifying micro- and macroperforations and their exact location as well as apposition of the perforation to the overlying stroma after suturing on the graft, determining the amount of residual stroma left in the case of pre-Descemetic DALK, detecting presence of interface fluid after suturing the donor graft, and so on. 13
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