Lamellar Keratoplasty

With advances in instrumentation and techniques, the selective removal of corneal tissue (lamellar keratoplasty [LK]) has become more popular. The general ophthalmologist should be familiar with the special indications for and limitations of the major techniques of LK, including SALK, DALK, DSEK, and DMEK (see Table 15-3). DSEK and DMEK are discussed separately later in this chapter.

Anterior Lamellar Transplantation

Lamellar corneal grafting may be indicated in patients who present with opacities or loss of tissue that, for the most part, does not involve the full thickness of the cornea. These conditions include

superficial stromal dystrophies and degenerations (eg, Reis-Bücklers dystrophy, Salzmann nodular degeneration, band keratopathy)

superficial corneal scars

multiple recurrent pterygium with visually significant corneal scarring

corneal thinning (eg, Terrien marginal degeneration, descemetocele formation, pellucid marginal degeneration) (Fig 15-13)

superficial corneal tumors congenital lesions (eg, dermoid)

corneal perforations that are not amenable to resuturing or that occur in patients with ocular surface disease (eg, keratoconjunctivitis sicca)

keratoconus

selective infections, including Acanthamoeba keratitis

Figure 15-13 A, Descemetocele in a patient with rheumatoid arthritis. B, Same patient after lamellar keratoplasty.

Advantages

LK has the following advantages over PK:

minimal requirements for donor material (as preservation of endothelium is not mandatory) reduced risk of entry into the anterior chamber (avoids risks of glaucoma, cataract, retinal detachment, cystoid macular edema, expulsive hemorrhage, and endophthalmitis)

shorter wound healing time and convalescence

reduced incidence of allograft rejection due to no risk of endothelial rejection and, consequently, decreased need for topical corticosteroids

reduced risk of traumatic wound rupture

improved long-term endothelial cell viability and increased graft longevity

better prognosis for patients who have poor adherence to medical instructions or difficulty obtaining frequent follow-up

Disadvantages

Anterior LK does not replace damaged endothelium. The procedure is more technically demanding and time-consuming than PK. It may be associated with opacification and vascularization of the interface. Descemet detachment may produce a double anterior chamber, and placement of an air bubble to tamponade the Descemet membrane against the stroma can lead to the development of an anterior subcapsular cataract.

Surgical Technique

Superficial anterior lamellar keratoplasty

SALK may be performed when the opacity is superficial. If there is a peripheral opacity or perforation, manual lamellar dissection is followed by placement of appropriately sized thin donor tissue.

To treat a central corneal opacity, SALK can be performed in 1 or 2 stages. In the 2-stage procedure, the initial step is to use a microkeratome to create a lamellar flap that encompasses the corneal pathology. This is useful only if the corneal surface is regular, because if there is irregularity, the microkeratome will produce an irregular corneal bed. The flap is lifted to ensure that the underlying stroma is clear and then replaced. After a 4- to 6-week interval that allows the flap to stabilize and partially adhere, the second stage is performed. A trephine is centered over the pupil and used to incise the previously made flap to a depth slightly below the initial lamellar dissection, ideally leaving a 1-mm flap rim. A blunt spatula is gently introduced at the plane of the lamellar flap, and the abnormal tissue is separated and lifted off. The donor tissue is then prepared using an artificial anterior chamber and a microkeratome with the same thickness head as in the initial procedure. A trephine of the same or a slightly oversized (0.25 mm) diameter is used to excise the tissue. The donor disk is then transferred to the host bed and, if there is a good match, the donor tissue may adhere spontaneously without sutures, although 10-0 nylon sutures can be used to anchor the graft and ensure proper alignment. A bandage lens can also be placed to facilitate adherence. In the 2-stage approach, the diameter of the host bed can be matched precisely with the diameter of the donor tissue with nice vertical incisions from trephination. Recently, the femtosecond laser has been used to perform the lamellar dissections of both the host and donor tissue in a single session.

Deep anterior lamellar keratoplasty

To obtain the best visual outcome, the interface must be smooth and clear, and almost all host stromal tissue must be removed. The Anwar big-bubble technique is the most widely used method of isolating Descemet membrane. If a big bubble cannot be produced, manual dissection is possible, but it risks loss of best-corrected visual acuity due to incomplete removal of the host stromal tissue. In an OCT study of patients who underwent DALK, 20 μm of residual stromal bed was not visually significant; however, 80 μm of tissue caused a reduction in vision.

The surgical technique for DALK begins with deep (at least 300 μm) trephination. Depending on surgeon preference, the anterior lamellae may be dissected and removed, leaving a thin layer of stroma, or left untouched. A tunnel is then fashioned from the deepest point of the trephination incision, extending 2–3 mm to the paracentral cornea and running parallel to the surface of the cornea to avoid perforation of Descemet membrane. Air is forcefully injected into the stroma and, hopefully, enters the pre-Descemet plane. If this step is successful, an air bubble outlined by a circular white band will suddenly appear. Specialized instruments—such as those developed by Dr Rajesh Fogla (Bausch + Lomb Instruments, St Louis, MO) and by Dr Donald Tan and Dr Vincenzo Sarnicola (both instruments available from ASICO, Westmont, IL)—aid in the performance of these maneuvers.

A limbal paracentesis is made to drain aqueous humor from the eye in order to reduce the pressure and help prevent perforation of the cornea while exposing Descemet membrane. The anterior wall of the bubble is then entered with a sharp 15° blade to create a 1-mm opening. Once incised, the bubble collapses; some surgeons then inject viscoelastic material into the collapsed bubble to help with the meticulous dissection. A spatula can be used to enter the pre-Descemet plane and advanced to the 6-o’clock position. When the spatula is lifted anteriorly, the stroma on the top of the spatula is incised using a sharp blade. As the stroma is severed, Descemet membrane is exposed. A similar maneuver is performed in the opposite direction. Blunt-pointed Vannas scissors and 0.12 forceps are used to make 2 long, perpendicular incisions, creating 4 quadrants of residual stroma; then each quadrant is excised, baring Descemet membrane. (Videos of this technique are available on the Internet.)

Only after recipient bed preparation is completed is the donor tissue prepared, because inadvertent entry into the anterior chamber requires conversion to a full-thickness PK. Inadvertent entry is not infrequent early in the learning curve, and it happens occasionally among experienced surgeons.

The donor tissue is prepared by punching an appropriate-sized button with a trephine. Trypan blue can be used to stain the endothelium to improve visualization in order to facilitate the removal of Descemet membrane and endothelium from the donor tissue. The donor tissue is then sutured into position using 10-0 nylon sutures in a continuous or interrupted fashion, as in a full-thickness PK.

Postoperative Care and Complications

Double anterior chamber or Descemet detachment

Descemet detachment or pseudo–double anterior chambers can occur because of fluid in the interface from a microperforation or retained viscoelastic material. Injection of air into the anterior chamber can help with resolution of the detachment; however, it may also reduce endothelial cell count and lead to the development of an anterior subcapsular cataract.

Opacification and vascularization of the interface

Meticulous irrigation and cleaning of the lamellar bed at the time of surgery reduces the likelihood of opacification. Retained interface debris, secondary vascularization, microbial infections, or wrinkles