Hyperguides

Ophthalmology / Refractive surgery

Automated Lamellar Therapeutic Keratoplasty

Charles A. Barsam MD Roy S. Chuck, MD, PhD
Article


Introduction

Lamellar corneal surgery originated in the pioneering works of Jose Ignacio Barraquer, MD, who was the first to report on both the theoretical and practical use of this surgical approach to modify the refractive state of the eye. Lamellar keratoplasty refers to the surgical procedure in which the anterior corneal layers to a variable stromal depth are excised and then replaced with donor tissue.1

In 1961, Barraquer demonstrated manual lamellar keratoplasty and, in 1972, microkeratome-assisted lamellar keratoplasty to correct refractive errors.2,3 Although the intervening years witnessed numerous modifications to these original surgical techniques, widespread acceptance was limited due to the technical difficulty in performing the classic manual technique and the lack of reproducibility with the first generation of microkeratomes.3 Free-handed deep lamellar dissection was frequently complicated by a 30% risk of inadvertent microperforation into the anterior chamber even in the hands of experienced surgeons.4 This complication often resulted in the unexpected conversion of the procedure to a full thickness penetrating keratoplasty (PKP) with less than optimal donor tissue.

The advent of LASIK surgery has generated a renewed interest in the development of microkeratomes that offer reliability and reproducibility of uniform incisions, as well as ease of use. Development of more accurate mechanical microkeratomes and more recently an all-laser microkeratome (Intralase, Irvine, Calif.) has reinvigorated interest in lamellar surgery and led to development of a novel surgical approach to the treatment of anterior stromal corneal opacities. Automated lamellar therapeutic keratoplasty (ALTK), the name given to this novel approach, offers an alternative to PKP for the appropriate surgical candidate with an intact corneal endothelium and corneal stromal disease.4 What differentiates this procedure from previous attempts at lamellar keratoplasty is the precision with which both the donor button and the recipient bed can be constructed. It is this accuracy that allows for a more precise interface between tissue layers that aids in tissue approximation and limits interface scarring.

Although PKP has been the mainstay of corneal transplantation, it is not without significant complications and lengthy visual rehabilitation. ALTK can serve as an adjunct to PKP and obviates the need for full thickness transplantation in patients with a healthy corneal endothelium and diseased stroma. ALTK offers the benefit of not having to enter the anterior chamber of the eye and therefore eliminates the risk of expulsive choroidal hemorrhage or endophthalmitis.5 Furthermore, by leaving the host's endothelium intact, there is less risk of endothelial failure in ALTK from allograft rejection than would be anticipated from PKP. Also, the postoperative recovery may be shorter and the visual rehabilitation faster in ALTK.5

The limitations to this procedure, beyond the obvious need to replace the endothelium in the various pathological conditions associated with loss of endothelial function, include conditions that result in abnormalities in ocular surface stability or variations in corneal thickness as in the case of corneal ectasias.4 Aside from the availability of improved microkeratomes that afford great accuracy of incision, the advent of the artificial anterior chamber has also facilitated ALTK.6 The artificial anterior chamber has enabled surgeons to obtain corneal lenticules from more readily available corneal-scleral rims as opposed to whole globes that are in shorter supply. The pairing of the mechanical microkeratome with an artificial anterior chamber has been labeled the ALTK System (Moria USA, Doylestown, Pa.). The ALTK system has been validated as an effective and reproducible means of creating corneal lenticules of varying size and depth.6,7 It is this precise pairing of donor lenticule with host tissue that has renewed enthusiasm for lamellar surgery.

Technique

The following surgical technique for ALTK was described by Jimenez-Alfaro and colleagues.4 Donor lenticules are obtained from the whole globes that are to be preserved in a fashion similar to that used in harvesting corneal caps. A microkeratome is used as a cutting instrument. The use of adjustable suction rings and plates enables the surgeon to create corneal incisions of varying depth and diameter. The microkeratome stop screw is not used so as to create a free cap.

The same process is repeated on the recipient eye with the intention of creating a free corneal lenticule with the same diameter and thickness as the donor corneal disc. The donor corneal lenticule is then positioned into the recipient bed and dried with sponges. The donor lenticule is allowed to set for 5 minutes within the donor bed before initial adhesion is assessed by means of depressing the host peripheral cornea. Adhesion is confirmed first by visualizing the indentation within the donor lenticule and then assessing lenticule positioning after a blink when the lid speculum has been removed. Should adhesion not be obtained, the lenticule can then be sutured into place using eight 10-0 nylon sutures. The patients are then examined at the silt lamp biomicroscope 2 hours after surgery for reevaluation of lenticular adhesion. The postoperative therapeutic regimen consists of topical antibiotics and steroids.

Azar and colleagues describe a variation of the aforementioned technique for lamellar keratoplasty; the technique involves the use of a hinged corneal flap.8 This technique differs mainly in the creation of a microkeratome-induced anterior corneal flap. Under this flap, the diseased region of stroma is excised by either trephination or laser ablation, and a complementary donor corneal button, created by an artificial anterior chamber system, is placed into the bed. The flap is then repositioned and is either sutured into position or held in place by a bandage contact lens. Due to flap creation, this procedure is limited in its ability to treat anterior stromal opacities.

Conclusion

These newer surgical techniques expand the array of procedures available for treatment of anterior corneal disorders. The advent of innovations in the field of refractive surgery has expanded the ability of surgeons to address disorders of the corneal stroma with renewed vigor. As compared to classic full thickness corneal transplantation, ALTK has numerous advantages in terms of intraoperative and postoperative complications.

References

  1. Melles GR, Remeijer L, Geerards AJ, Beekhuis WH. The future of lamellar keratoplasty. Curr Opin Ophthalmol. 1999;10(4)253-259.

  2. Barraquer JI. Keratoplasty. Arch Soc Am Oftalmol Optom. 1961;3:169-180.

  3. Barraquer JI. Lamellar keratoplasty. Special techniques. Ann Ophthalmol. 1972;4:437-469.

  4. Hanna KD, David T, Besson J, Pouliquen Y. Lamellar keratoplasty with the Barraquer microkeratome. Refract Corneal Surg. 1991;7:177-181.

  5. Jimenez-Alfaro I, Perez-Santonja JJ, Telleria GG, Bueno Palacin JL, Puy P. Therapeutic lamellar keratoplasty with an automated microkeratome. J Cataract Refract Surg. 2001;27(8):1161-1165.

  6. Behrens A, Dolorico AM, Kara DT, Novick LH, et al. Precision and accuracy of an artificial anterior chamber in obtaining corneal lenticules for lamellar keratoplasty. J Cataract Refract Surg. 2001;27:1679-87.

  7. Sarayba MA, Li L, Sweet PM, Chuck RS. A portable microkeratome-based anterior corneal surface harvesting device. Cornea. 2002;21(6):589-591.

  8. Azar DT, Jain S, Sambursky R. A new surgical technique of microkeratome assisted deep lamellar keratoplasty with a hinged flap. Arch Ophthalmol. 2000;118:1112-1115.