The concept of “match and patch” is to clearly define and regularize a semi-circular “C”-shaped or “banana”-shaped area of tissue immediately around the peripheral melt, which fully encompasses the melting area, but minimally involved unaffected corneal tissue, using calipers and various circular trephines of predetermined diameters, and then to replicate this same shape in the donor cornea. The donor tissue is therefore carefully sized to “match” the recipient bed, and “patches” the peripheral defect accordingly.

Ideally, lamellar dissection of the recipient bed should be performed carefully to avoid inadvertent perforation, but also to regularize the overall depth of bed dissection so as to prevent an irregular surface contour when the donor is sutured on. If the dissection is deep enough, i.e., within 100–150 microns of Descemet’s membrane (DM), then a full thickness donor tissue patch may be simply utilized, after peeling away the underlying DM. However, if only half thickness dissection of the recipient bed is performed, then a similar half thickness lamellar dissection of the donor cornea should be performed.

The surgery is preferably done under general anesthesia, as the duration of surgery may take an excess of 1–2 h, but could be done under regional anesthesia, as the procedure is essentially extraocular. After the patient is cleaned and draped, the area of dissection is measured using a pair of calipers to determine the optimum corneal graft size. Conjunctival peritomy is performed adjacent to the area of thinning. Marking corneal trephines and dermatological trephines are used to mark the cornea and delineate the dissection bed in a structured step-by step technique (Fig. 11.2).

The outer and inner circumferential limits of the area of thinning are marked with corneal trephines. The distance between the two arcs is measured using a pair of calipers at the two edges of the melt and at the midpoint of the dissection bed. Dermatological trephines of appropriate sizes (or nearest size) are used to mark the edges of the dissection bed. The furthest distance between the two corners of the dissection bed is measured. This completes the outline of the C-shaped dissection bed. The use of marking trephines allows regularization of the area of dissection and subsequent replication of the same matching shape on the donor cornea. The area of dissection may include adjacent sclera depending on the extent of melt.

Freehand partial thickness vertical dissection of the marked area to attain vertical and regular graft margin is performed using a diamond blade. Care is taken to avoid causing an inadvertent perforation. A smooth and regular vertical edge of the dissection bed is ideal for good apposition of donor graft-to-host, especially during suturing. Careful lamellar dissection is performed with a crescent blade, a mini-crescent blade or similar lamellar dissector, while ensuring that a reasonably uniform dissection bed is created.

Intraoperative pachymetry can be used to guide the depth of dissection. The dissection bed is kept dry so that in the event of perforation, aqueous leak can be quickly identified.

In the event of a perforation, intra-cameral air can be injected to stabilize the anterior chamber. Lamellar dissection should then be performed at unaffected areas of the dissection bed first, leaving the area of perforation to be tackled last. In cases of existing perforation, the same principles of lamellar dissection all around the perforation site can be utilized, leaving the perforation site to be dissected last. It is generally easier to continue lamellar bed dissection if the chamber remains formed with air, but in cases of larger perforations where this is not possible, the hole may be temporally sealed with fibrin glue or histoacryl glue, so as to complete lamellar dissection, or else it is still possible to complete lamellar dissection with iris plugging the wound and a flat chamber. The donor tissue can then be used to tamponade the perforation site, and after suturing the donor in place, any iris adhesions or synechiae may be released with a sinsky hook introduced from a separate paracentesis. In cases of a large perforation, which is likely to cause a double chamber in the postoperative period, denoting separation of the recipient lamellar bed and the donor, a large air bubble tamponade coupled with dilatation of the pupil or an inferior peripheral iridotomy (to prevent pupillary block) should be considered.