Several surgical approaches available for patients with limbal stem cell deficiency
A systematic approach is needed for ocular surface reconstruction.
Global bilateral blindness is estimated by the World Health Organization to be around 45 million people, of which more than 20% are secondary to corneal diseases. Of all the corneal disorders, limbal stem cell deficiency may be considered as one of the most severe and difficult-to-treat clinical entities.
Limbal stem cells are of significant importance with regard to corneal homeostasis. They form a somewhat circular garland on the ocular surface, sandwiched between the corneal and conjunctival epithelia. Human limbal stem cells can be detected both in vivo and in vitro by their expression of p63 transcription factor. The protein p63 retains the proliferative potential of limbal stem cells. These stem cells maintain corneal stromal avascularity and corneal epithelial integrity and thus play a vital role in the sustenance of a clear cornea, which is essential to vision. In the absence of a viable, healthy stem cell population, conjunctival progression to the corneal territory and vascular invasion of the cornea can result in a cloudy or opaque cornea and can potentially lead to corneal blindness. In cases of such corneal blindness, an allogenic corneal transplantation such as a penetrating keratoplasty can provide a clear cornea and restore vision only temporarily because conjunctival cell invasion onto the grafted cornea will lead to possible blindness. Hence, any attempt at vision restoration must first address the restoration of the limbal stem cells.
Limbal stem cell restoration may be approached from various routes. These include autologous culture of limbal cells as a source of transplant tissue; conjunctival limbal autograft; living-related conjunctival allograft; and keratolimbal allograft using a donor cornea from the eye bank. Once limbal stem cells have been established, then corneal opacity may be addressed in terms of partial-thickness anterior lamellar keratoplasty, full-thickness penetrating keratoplasty, or an artificial cornea such as the Boston keratoprosthesis, depending on the extent of the corneal damage.
Under optimal culture conditions, human keratinocytes generate holoclones, meroclones and paraclones. Holoclone-forming cells are the stem cells of almost all human squamous epithelia and are located in the limbus. The discovery that human limbal cell cultures contain holoclones resulted in the first therapeutic application of such cultures for the purpose of corneal epithelial regeneration. Although this technique is utilized in other parts of the globe, it is currently not available in the United States as a technique approved by the U.S. Food and Drug Administration. Hence, the other three surgical options may be considered, depending on the extent of limbal stem cell deficiency and whether the involvement is unilateral or bilateral.
In this column, Drs. Chan and Holland describe their surgical approach to limbal stem cell deficiency.
Thomas “TJ” John, MD
OSN Surgical Maneuvers Editor
Ocular surface reconstruction requires a systematic approach. The ophthalmologist should first reliably make the diagnosis of limbal stem cell deficiency (LSCD). Staging of disease severity needs to be considered. Control of glaucoma and optimizing the lids, tear film and conjunctival inflammation must occur before any limbal stem cell transplantation (LSCT) surgery.
Patients with LSCD may present with decreased vision, foreign body sensation or photophobia. Clinical findings include various combinations of conjunctivalization of the cornea with vascularization and pannus (Figures 1 and 2); corneal scarring or haze (Figure 2); a wave-like late fluorescein staining pattern (Figure 3); persistent or recurrent epithelial defects; and keratoplasty failure. Patients may have associated conjunctival disease: symblepharon, loss of the fornices, surface keratinization and mucin deficiency.
Images: Chan CC, Holland EJ
The preoperative staging of ocular surface disease is important when deciding upon the type and timing of LSCT. Ocular factors include laterality, extent of LSCD and extent of conjunctival disease. Additional factors include extent of stromal scarring, mechanical eyelid problems, glaucoma and retinal disease. Non-ocular factors include age, systemic health and compliance ability. In cases of simple focal LSCD, only limbal reconstruction is required. In complicated cases, a step-by-step approach is taken.
Conjunctival limbal autograft surgery
Conjunctival limbal autograft (CLAU) surgery (Figure 4) is performed in partial or total unilateral LSCD. The fellow eye must be normal with no limbal stem cell problems. A 360° conjunctival peritomy is performed in the recipient eye, then superficial keratectomy of any corneal pannus. In the donor eye, 2 to 3 clock hours of limbus from superior and inferior locations and 2 mm to 3 mm of conjunctiva are marked. The conjunctiva is dissected toward the adherent portion at the limbus. Reflect the conjunctiva over the cornea and dissect with a crescent blade, a shallow depth of 1 mm onto the cornea, before amputation of the graft to ensure the stem cells are harvested. The grafts are stored in a sterile Petri dish with balanced salt solution. The donor sites are sutured with 8-0 Vicryl or tissue glue. When placing the donor tissue, interrupted 10-0 nylon sutures ensure that each CLAU graft is secure at the limbus. Tissue glue is used to secure the base of the graft. A bandage contact lens is placed. Topical steroids and antibiotics are used four times daily and tapered as the cornea re-epithelializes. Non-preserved artificial tears are used liberally.
Living-related conjunctival limbal allograft surgery
Living-related conjunctival limbal allograft (LR-CLAL) surgery (Figures 4 and 5) can be performed in cases of bilateral, partial or total LSCD. The donor tissue is usually from a sibling or parent. Donor and recipient immunologic matching is possible based on ABO blood type and human leukocyte antigens. Recipient and donor preparation, along with graft placement, is similar to that for CLAU.
Keratolimbal allograft surgery
Keratolimbal allograft (KLAL) surgery (Figures 6 and 7) is for unilateral severe LSCD in which the fellow eye has risk for limbal disease or bilateral severe LSCD and there is no available living-related donor. The corneoscleral rims from both eyes of one donor are used for one recipient eye. The recipient eye is prepared in the same fashion as in CLAU or LR-CLAL surgery. The KLAL donor corneoscleral rim is trephined with a 7.5-mm blade as in routine penetrating keratoplasty. The rim is cut in half and trimmed, leaving 2 mm to 3 mm of sclera. The posterior sclera and corneal stroma of each segment are removed using lamellar dissection techniques with a crescent blade and curved Vannas scissors. When each graft is secured at the limbus with two 10-0 nylon sutures, the corneal edge then sits smoothly on the plane of the cornea, avoiding a step. The segment length can be trimmed to avoid overlap. Tissue glue secures the base of the grafts to recipient sclera and the posterior edge to the conjunctiva. Avoid gaps between the KLAL lenticules, where conjunctival invasion could occur. After subconjunctival antibiotics and steroid, a large bandage contact lens with a diameter of 18 mm to 20 mm is placed.
In cases of severe bilateral conjunctival and limbal disease with significant symblepharon formation, LR-CLAL has been used in combination with KLAL at the 3 and 9 o’clock meridians to prevent conjunctival invasion. In unilateral cases, CLAU can be used in combination with KLAL lenticules. In these procedures, only one corneoscleral rim is needed (Figure 8).
Topical steroids and cyclosporine, and oral prednisone, tacrolimus and mycophenolate mofetil are necessary in all patients who receive any form of allografts to prevent rejection. For successful LSCT, multiple factors need to be optimized preoperatively. As ex vivo techniques are refined, they will be useful, especially for patients with bilateral disease. Until then, CLAU, LR-CLAL, KLAL and combination surgeries are viable options to rehabilitate patients with LSCD.