• Cornea/External Disease

    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.

    Image courtesy Bennie Jeng, MD.
    Figure 1. Diffuse-illumination after DALK for keratoconus.

    Image courtesy Bennie Jeng, MD.
    Figure 2. Slit-beam view demonstrates a trace amount of interface haze.


    Ardjomand et al (Am J Ophthalmol. 2007;143(2):228–235) performed a study in which 32 eyes of 23 patients who underwent DALK or PK were analyzed for objective measurements of visual quality. They found that overall, the eyes that had undergone PK had statistically significantly better visual acuity than the DALK group, but subgroup analysis of the DALK eyes revealed that the level of visual acuity was related to the thickness of the residual corneal stromal bed. Eyes with a residual stromal bed of <20 µm had similar visual acuities to the eyes that underwent PK, while eyes with a residual stromal bed of >80 µm had statistically significantly reduced visual acuity. Contrast sensitivity and higher-order aberrations were not statistically different between the DALK and PK eyes.

    On the Horizon

    As technology evolves, newer methods of performing DALK will certainly arise. In addition to advancements in dissection techniques to bare Descemet’s membrane, improved methods for securing the donor cornea to the host bed are also being investigated. Narendran et al (Cont Lens Anterior Eye. 2007) used fibrin glue with overlay sutures that are removed only 4 weeks after surgery and found that it has potential for significantly reducing operative time.

    Other researchers are also studying the use of the femtosecond laser for lamellar dissection,9-10 and preliminary results demonstrate that it is very accurate even at depths of 500 µm (J Refract Surg. 2007;23(1):58–65). Unfortunately, for eyes with keratoconus (as well as some other stromal opacities), creating an accurate-thickness cut when measured from the anterior surface results in irregular thicknesses of the residual stromal bed. This technology is not yet able to measure thickness from the posterior surface to allow for the creation of a stromal bed with a consistent thickness, and it cannot yet be used to bare Descemet’s membrane. However, further advancements in this technology are promising.

    Conclusions

    For corneal pathologies that do not involve Descemet’s membrane and the endothelium, DALK is an excellent alternative to full-thickness corneal transplantation. The anatomical success rate in performing DALK by experienced surgeons is very good, and, with this procedure, the issue of endothelial rejection is obviated, although stromal rejection can still occur. Various techniques are available for use when attempting to bare Descemet’s membrane, but it appears that as long as no more than 20 µm of stromal tissue is left in the host bed, visual outcomes seem to be comparable to those of PK. Because of the learning curve involved in performing this procedure and the additional time it requires, many surgeons have not routinely adopted DALK as the procedure of choice for anterior corneal pathologies, but with improved technology, this may soon change.

    References

    1. Shimmura S, Tsubota K. Deep anterior lamellar keratoplasty.Curr Opin Ophthalmol. 2006;17(4):349–355.
    2. Anwar M, Teichmann KD. Big-bubble technique to bare Descemet’s membrane in anterior lamellar keratoplasty.J Cataract Refract Surg. 2002;28(3):398–403.
    3. Melles GR, Lander F, Rietveld FJ, et al. A new surgical technique for deep stromal, anterior lamellar keratoplasty.Br J Ophthalmol. 1999;83(3):327–333.
    4. Al-Torbak AA, Al-Motowa S, Al-Assiri A, et al. Deep anterior lamellar keratoplasty for keratoconus.Cornea. 2006;25(4):408–412.
    5. Fontana L, Parente G, Tassiniari G. Clinical outcomes after deep anterior lamellar keratoplasty using the big-bubble technique in patients with keratoconus.Am J Ophthalmol. 2007;143(1):117–124.
    6. Noble BA, Agrawal A, Collins C, et al. Deep anterior lamellar keratoplasty (DALK): visual outcome and complications for a heterogeneous group of corneal pathologies.Cornea. 2007;26(1):59–64.
    7. Ardjomand N, Hau S, McAlister J, et al. Quality of vision and graft thickness in deep anterior lamellar and penetrating corneal allografts.Am J Ophthalmol. 2007;143(2):228–235.
    8. Narendran N, Mohamed S, Shah S. No sutures corneal grafting: a novel use of overlay sutures and fibrin glue in deep anterior lamellar keratoplasty [published online ahead of print March 20, 2007]. Cont Lens Anterior Eye.
    9. Sarayba MA, Maguen E, Salz J, et al. Femtosecond laser keratome creation of partial thickness donor corneal buttons for lamellar keratoplasty.J Refract Surg. 2007;23(1):58–65.
    10. Suwan-Apichon O, Reyes JM, Griffin NB, et al. Microkeratome versus femtosecond laser predissection of corneal grafts for anterior and posterior lamellar keratoplasty. Cornea. 2006;25(8):966–968.

    Author Disclosure

    Dr. Jeng states that he has no financial relationship with the manufacturer of any product discussed in this article or with the manufacturer of any competing product.