Femtosecond laser creates thin corneal graft for limbal stem cell transplantation

Issue: January 25, 2009

BySuk Kyue Choi, MD

ByJin Hyoung Kim, MD

ByDoh Lee, MD, PhD

Introduction
Healthy human corneal stem cells reside at the limbus and act as a barrier, preventing adjacent conjunctival tissue from invading the cornea and at the same time functioning as a source of corneal epithelial cells.

Some of the unique characteristics of stem cells include longevity, high capacity of self-renewal, long cell cycle time, increased potential for error-free proliferation and poor differentiation. Damage to these stem cells results in stem cell deficiency that causes loss of the barrier function and conjunctivalization of the cornea, which leads to corneal vascularization, irregular surface epithelium with goblet cells and patient discomfort.

Thomas John

Management of stem cell deficiency can be difficult and challenging. Although partial stem cell deficiency may be managed in some cases by selective removal of the abnormal epithelium and allowing the defect to be healed by cells derived from the intact limbal epithelium, total stem cell deficiency requires transplantation of autologous limbus from the opposite normal eye or homologous limbus from living related-donor or cadaveric-donor. In non-autologous donor transplantation, systemic immune-suppression is needed.

Surgical technique for limbal stem cell transplantation should take into consideration the following: good approximation at the donor-recipient junction; thin donor tissue; avoidance of damage to donor stem cells; and optimal preparation of the recipient bed. Thin donor graft will help in a more even spread of the tear film on the ocular surface and less discomfort for the patient. This is surgically challenging and difficult to achieve in a fully manual surgical technique.

Doh Lee, MD, PhD, Jin Hyoung Kim, MD, and Suk Kyue Choi, MD, describe their surgical technique for limbal stem cell transplantation with the use of a femtosecond laser combined with manual dissection. This new application of the femtosecond laser in anterior segment surgery is an interesting surgical approach, but continued efforts at improving and refining techniques are essential to overcome hurdles such as increased corneal stromal scarring, use of the laser in the far periphery of the cornea closer to the limbus and irregular corneas with significant corneal stromal neovascularization.

This new surgical technique in performing limbal stem cell transplantation needs to be further evaluated for the ease of use and reproducibility.

– by Thomas John, MD
OSN Corneal Dissection Editor

by Doh Lee, MD, PhD, Jin Hyoung Kim, MD, and Suk Kyue Choi, MD

The preferred anesthesia is with a retrobulbar block. However, other forms of anesthesia, including general anesthesia, may be considered.

Figure 1: Schematic representation of the donor globe

Schematic representation of the donor globe, showing preparation of the donor cornea. After the creation of the corneal button for penetrating keratoplasty, a diamond blade was used to extend the cut to the periphery of the sclerocorneal rim before transplantation (black dotted line).

Figure 2: Donor preparation using femtosecond laser

Donor preparation using femtosecond laser for both PK and for limbal graft consisting of limbal stem cells. The femtosecond laser is used first to create the full-thickness cut from the endothelial to the epithelial surface followed by the ‘ring procedure’ (inner side cutting) that creates the lamellar dissection for stem cell transplantation.

Preparation of the donor cornea

The whole eyeball is preferred for the preparation of the donor tissue for limbal transplantation because sufficient limbal tissue can be obtained. Central and peripheral corneal thickness is measured on both the donor and recipient corneas using an ultrasound ophthalmic pachymeter. This helps in the surgical planning to obtain the thinnest donor graft and well-approximated donor-recipient wound edges. The preparations of the graft for limbal transplantation — namely, a lamellar graft and, for the keratoplasty, a full-thickness graft — are simultaneously performed. In the United States, one donor cornea or globe cannot be used on two different patients.

The parameters of the femtosecond laser are as follows: The energy to create each dissection is 0.78 µJ. The spacing between each laser spot and raster line is 5 µm × 5 µm. The side cut energy is 1 µJ, and the side cut angle is 90·. The diameter is determined based on the size of the penetrating keratoplasty.

After stabilization of the donor globe with a fixation device, a suction ring was placed on the globe, and the applanation cone is placed on the cornea (Figure 1). After laser dissection from the endothelium to the epithelium of the donor cornea for PK, the inner side cutting and lamellar cutting was performed for the lamellar graft. The outer side cutting was not performed (Figure 2). After the cornea button was removed, further lamellar dissection to the periphery of the corneoscleral rim is performed using a diamond knife through the space pretreated with IntraLase (Advanced Medical Optics) (Figure 3).

Figure 3: A diamond knife is used to complete the most distal part of the lamellar dissection

A diamond knife is used to complete the most distal part of the lamellar dissection to harvest the donor stem cells within a thin lamellar donor graft.

Figure 4: Recipient corneal preparation using the femtosecond laser

Recipient corneal preparation using the femtosecond laser. The ring procedure with the femtosecond laser creates the lamellar separation of the recipient cornea.

Figure 5: Removal of unhealthy recipient limbal tissue

Removal of unhealthy recipient limbal tissue using femtosecond laser followed by manual dissection.

Figure 6: After amniotic membrane transplantation

After amniotic membrane transplantation, the donor limbal graft is placed on the recipient cornea, and several radial interrupted 10-0 nylon sutures are placed between the donor and recipient corneal tissue and between the outer margins of the donor graft and the recipient sclera.

Images: Lee D

Preparation of the recipient cornea

The preparation of recipient donor for limbal transplantation is performed with the femtosecond laser. The same femtosecond laser parameters as in the donor cornea are used to perform the ring procedure on the recipient cornea (Figure 4). Unlike the donor cornea, no full-thickness cut is made in the recipient cornea. The parameters of the laser are adjusted based on the condition of the recipient cornea. The laser setting on the recipient cornea is almost the same as the laser parameters on the donor preparation. In areas of severe corneal scarring, the femtosecond laser dissection may be incomplete. If necessary, in such focal areas of incomplete laser dissection, manual dissection with a diamond knife can be used. After the removal of unhealthy limbal tissue (Figure 5), conjunctival recession and freeze-dried amniotic membrane transplantation are performed to promote wound healing.

Transplantation of the limbal graft

The donor limbal graft is placed on the recipient cornea. Six or more radial interrupted 10-0 nylon sutures are used to approximate donor and recipient corneal tissue edges followed by several radial interrupted sutures that are placed between tissues of the donor graft and recipient sclera (Figure 6). A bandage contact lens was applied at the completion of limbal transplantation procedure.

Surgical pearls and tips

Pachymetric measurement of the donor and recipient corneas is an important step for surgical planning and tissue preparation.
The key points of limbal transplantation are how thin the donor tissue is made and how accurately the donor-recipient tissue is aligned. The femtosecond laser facilitates the preparation of a thin donor limbal graft.
There are instances in which the recipient cornea could not be prepared successfully, especially in cases of severe focal scarring. In such cases, careful manual dissection is carried out in those focal areas.
Careful approximation of the inner circular edge of the donor-recipient tissue is mandatory for the overall success of this procedure.
Immunologic rejection is common in limbal transplantation because of the abundance of the Langerhans cells in limbal tissue. The appropriate management with immune suppressant is needed in limbal transplantation.

Drug regimen and follow-up

Preoperatively, an antibiotic eye drop such as Iquix (levofloxacin 1.5%, Vistakon) is used four times a day for 3 days before surgery. Postoperatively, a topical steroid, Pred Forte 1% (prednisolone acetate 1%, Allergan), levofloxacin 1.5% and preservative-free artificial tears are used four times daily.

References:
Dua HS, Azuara-Blanco A. Limbal stem cells of the corneal epithelium. Surv Ophthalmol. 2000;44(5):415-425.
Kim JY, Djalilian AR, Schwartz GS, Holland EJ. Ocular surface reconstruction: limbal stem cell transplantation. Ophthalmol Clin North Am. 2003;16(1):67-77.
Meisler DM, Perez VL, Proudfit J. A device to facilitate limbal stem cell procurement from eye bank donor tissue for keratolimbal allograft procedures. Am J Ophthalmol. 2005;139(1):212-214.
Shi W, Gao H, Wang T, Xie L. Combined penetrating keratoplasty and keratolimbal allograft transplantation in comparison with corneoscleral transplantation in the treatment of severe eye burns. Clin Experiment Ophthalmol. 2008; 36(6):501-507.
Wylegala E, Dobrowolski D, Tarnawska D, et al. Limbal stem cells transplantation in the reconstruction of the ocular surface: 6 years experience. Eur J Ophthalmol. 2008;18(6):886-890.
Thomas John, MD, is a clinical associate professor at Loyola University at Chicago and is in private practice in Tinley Park and Oak Lawn, Ill. He can be reached at 708-429-2223; fax: 708-429-2226; e-mail: tjcornea@gmail.com.
Doh Lee, MD, PhD, Jin Hyoung Kim, MD, and Suk Kyue Choi, MD, can be reached at Department of Ophthalmology, Ilsan Paik Hospital College of Medicine, Inje University, Korea; 82-31-910-7240; fax: 82-31-911-7241; e-mail: eyedr0823@hotmail.com.