8.1 Introduction

Patch grafts are usually needed in localized corneal problems for either tectonic or therapeutic reasons. In these cases, full penetrating keratoplasties may be unnecessary or not appropriate. Patch grafts may also be used temporarily in urgent situations where good quality corneal tissue for a penetrating keratoplasty is not immediately available. The most common indications are localized loss of tissue and infectious keratitis. Peripheral pathology is particularly suitable for patch grafts as the pathology often resolves without needing any further definitive treatment. Some of the common indications for patch grafts are seen in ▶Table 8.1. Patch grafts may be constructed from corneal tissue, conjunctival tissue, amniotic membranes, or even synthetic materials. ¹

8.2 Mini Patch Grafts

Localized peripheral infectious keratitis, especially deep keratomycosis, and localized traumatic tissue loss are good indications for small corneal grafts. In these cases, as the central cornea is unaffected, patching the peripheral area alone can decrease the long-term complications of traditional corneal transplantation. Lamellar or full-thickness patches may be performed, depending on the depth of the pathology. As the area covered by these grafts is very small and peripheral, graft rejection or endothelial failure is usually not significant even in full-thickness grafts as the host endothelium can replace this limited area easily. Another advantage is that corneal tissue that would not typically be useful for traditional keratoplasty can be used for patch grafting. Therefore, tissue with low endothelial cell counts or stromal opacities may be used. Irradiated and glycerol-preserved tissues, which have long shelf lives, can be kept on hand and used emergently in this manner. Tissue left over from small incision lenticule extraction surgery or Descemet’s stripping endothelial keratoplasty stromal caps may be used, and one cornea can be used for multiple grafts.

A dermal punch of appropriate diameter (usually 3.0, 3.5, or 4.0 mm) is selected and used to cut the host and donor cornea (▶Fig. 8.1). The same size can be used for both corneas. In case of a lamellar transplant, dissection is performed of the host cornea to remove the necrotic tissue. Alternatively, the punch is used to punch out a full-thickness button of the host cornea encompassing the entire pathology. The donor corneal button is then sutured into position using 6 to 8 sutures (▶Fig. 8.2). Sutures close to the pupil are usually placed more obliquely to avoid distorting the visual axis (▶Fig. 8.3). It is seldom necessary to redo these transplants for the above reasons and they usually incorporate well into the host cornea, obviating the need for further procedures. ²

8.3 Crescent Grafts

These require a little more skill to construct but are particularly good for pathologies that result in peripheral melts in a crescentic fashion like peripheral ulcerative keratitis from autoimmune diseases such as rheumatoid arthritis or granulomatosis with angiitis (formerly called Wegener’s granulomatosis) (▶Fig. 8.4). Degenerative conditions, such as Terrien marginal degeneration or Pellucid degeneration, also result in severe peripheral thinning in a crescent fashion. All these conditions can perforate either spontaneously or with minimal trauma. Performing a traditional penetrating keratoplasty in these situations would require a very large transplant, and its proximity to the limbus would increase the risk of rejection. Rejection of a crescentic graft, however, is not as significant as a mini-graft, and the endothelial surface area is much smaller and can be replaced by host endothelium. Crescent transplants can be full-thickness or, if the corneal endothelium is intact and the melt or defect is localized to the stroma and endothelium, a lamellar graft can be performed in a similar manner. ³

The graft is constructed first by marking the host corneal pathology with two trephines. The first trephine is approximately the diameter of the cornea and is placed peripheral to the pathology. The second trephine is 2 to 3 mm larger, based on the size of the pathology. It is placed just central to the innermost aspect of the pathology (▶Fig. 8.5). The cornea is then cut out with scissors along the marks created by the two trephines. The same trephines are then used to punch the donor cornea in a similar fashion. The crescent graft is then sutured into place using interrupted or running sutures (▶Fig. 8.6). Similar to the mini-graft, multiple crescent grafts can be fashioned from one donor cornea and corneal tissue not suitable for traditional transplantation may be used.