The donor button is secured with at least 4 interrupted cardinal sutures. The second cardinal suture is the most important because a mistake at this stage in anchoring the button 180° away from the first suture has the greatest mathematical potential, in principle, for misalignment error and subsequent astigmatism. Complete wound closure is achieved with interrupted sutures, 1 or 2 continuous sutures, or a combination.
The suture knots may be positioned in either donor or host tissue and are buried in the corneal stroma, not left in the wound interface. Most corneal surgeons prefer deep partial-thickness corneal suture bites over full-thickness bites. Incorporating 95% of the donor’s and host’s relative corneal thickness avoids posterior wound gape. Full-thickness bites may be associated with a higher chance of leakage along suture tracks and serve as a portal of entry for microorganisms or epithelial ingrowth. The advantages of deep suture placement with either technique are decreased posterior wound gape and enhanced wound stabilization and healing.
A variety of techniques are used to complete the suturing, depending on the clinical situation and preference of the surgeon. Vascularized, inflamed, or thinned corneas tend to heal unevenly and unpredictably. Interrupted sutures, usually 16–24 in number, are the technique of choice in such corneas, as well as in pediatric keratoplasties, where wound healing is rapid (Fig 16-1). The tension of each interrupted suture acts as an independent vector, generating central steepening and local flattening. Sutures may be removed selectively in the presence of sufficient donor–recipient interface healing if they attract blood vessels or if they loosen because of wound contraction. Astigmatism may be reduced postoperatively by selective removal of sutures in the steep corneal meridian, although premature removal risks wound dehiscence or slippage.
In the absence of vascularization, focal inflammation, or thinning, single or double continuous sutures or combined interrupted and continuous sutures can be used to secure the PK (
Figs 16-2, 16-3Fig 16-2 and
Fig 16-3). If properly placed, continuous sutures may allow more even distribution of tension and healing around the wound. Suture passes may be placed radially to the donor–recipient wound or be placed torque-free. The advantages of running sutures include their ease of removal postoperatively. Disadvantages include sectoral loosening, or cheese wiring, which may compromise the entire closure.
The combined interrupted and continuous suture technique offers several of the advantages of both methods. The interrupted sutures may be removed earlier after PK in order to reduce corneal astigmatism, whereas the continuous suture remains to protect against wound dehiscence. There is no consensus as to whether the combined technique or the running techniques produce less astigmatism. Many variables contribute to astigmatism, but the key suturing principle is uniform placement to minimize uneven suture tension, tissue torque, and distortion, thereby achieving secure closure without override or posterior wound gape.