Despite the possibility of endothelial rejection, full-thickness corneal transplantation is still considered the gold standard surgery for replacing a diseased cornea. Deep anterior lamellar keratoplasty (DALK) is not a new procedure, but in the past, its use has been of limited popularity owing to the lengthy and tedious surgery involved. With the advent of newer surgical techniques and instruments for performing lamellar corneal surgery, DALK has gained in popularity. This article discusses the techniques for performing the procedure as well as the clinical outcomes, especially compared with the outcomes of penetrating keratoplasty (PK).
Indications for DALK
Deep anterior lamellar keratoplasty is an excellent alternative to penetrating keratoplasty in eyes with normal Descemet’s membrane and endothelial cells. The most common indication for this procedure is keratoconus, as long as there is no history or evidence of hydrops. Other indications include any stromal opacity such as stromal dystrophies and stromal scars that do not involve Descemet’s membrane.
Surgical Technique
Modern techniques of DALK aim to bare Descemet’s membrane. A myriad of techniques have been proposed and used by various surgeons in an effort to predictably bare the membrane without perforation; these were summarized by Shimmura and Tsubota (Curr Opin Ophthalmol. 2006;17(4):349–355). The traditional mechanical technique involves the removal of host tissue layer by layer until Descemet’s membrane is bared. This technique is very time-consuming, and many alternative methods have been proposed. These include intrastromal air injection, viscodissection, and the “big-bubble??? technique (J Cataract Refract Surg. 2002;28(3):398–403). A sclerolimbal approach has also been described by Melles (Br J Ophthalmol. 1999;83(3):327–333).
Intraoperative Complications
The main intraoperative complications of performing DALK are the inadvertent creation of a Descemet’s membrane perforation or a pseudo-anterior chamber. To manage a small perforation, the surgeon can use an intracameral injection of air and then continue with the dissection. Larger holes or tears require either suturing the torn membrane or converting to a PK. A pseudo-anterior chamber can occur intraoperatively or postoperatively. In either case, this complication can be managed by intracameral injection of sulfur hexafluoride (SF6) gas to tamponade the Descemet’s membrane against the graft.
Outcomes
Outcomes of DALK for keratoconus have been shown to be excellent by Al-Torbak et al (Cornea. 2006;25(4):408–412), Fontana et al (Am J Ophthalmol. 2007;143(1):117–124), and Noble et al (Cornea. 2007;26(1):59–64). In Al-Torbak et al, baring of Descemet’s membrane occurred in 37% of 127 eyes of 118 patients. Intraoperative Descemet’s membrane perforation occurred in 13% of cases, and stromal rejection occurred in 3.1% of eyes. At the last follow-up visit, 74% of the eyes achieved a best-corrected visual acuity (BCVA) of 20/50 or better, compared to 9% preoperatively. In eyes that had Descemet’s membrane bared, 93.7% achieved a BCVA of 20/50 or better, compared to 62.5% or eyes that did not have Descemet’s membrane bared.
In Fontana et al, the big-bubble technique was used to perform DALK. Ninety-six percent of 81 eyes of 81 patients were successfully completed with DALK, and a big bubble was achieved in 64% of cases, with the remaining cases completed by manual dissection. Intraoperative microperforations occurred in 11 cases, but only 3 cases required conversion to PK. While the overall best-spectacle-corrected visual acuity (BSCVA) improved from 20/100 preoperatively to 20/30 postoperatively, the final BSCVA was statistically significantly better in the eyes in which Descemet’s membrane was bared using the big-bubble technique. Interface opacities were noted in 12 of the 28 cases where manual dissection was used to complete the surgery, compared to none of the 50 cases successfully performed using the big-bubble technique, but these interface opacities tended to clear during the first year postoperatively. The average endothelial cell density decreased by 9%, and stromal rejection occurred in 2 eyes.
In Noble et al, DALK was performed using the Melles sclerolimbal technique in 80 eyes of 68 consecutive patients with various corneal pathologies including keratoconus, herpes simplex virus keratitis, stromal dystrophies, stem-cell failure with scarring, corneal dermoid, and corneal opacity. Descemet’s membrane was perforated in 11 cases, and of these, 7 required conversion to PK. A BCVA of 6/6 or better was achieved in 24.7% of eyes, 6/9 or better in 69.9% of eyes, and 6/12 or better in 84.9% of eyes. Stromal rejection occurred in 7 eyes, but all were reversed with intensive topical corticosteroid therapy.
Descemet’s Membrane: To Bare or Not to Bare?
Although most surgeons’ goal with DALK is to bare the Descemet’s membrane, often this is not achieved and some stromal fibers are left in the host bed. It is believed that incomplete baring of Descemet’s membrane can lead to a higher chance of interface haze (Figures 1 and 2) and decreased quality of vision.