through the donor and host cornea. The depth of the suture is about 90% on both the donor and host tissues to prevent gapping of the wound. We prefer to use a surgeonÕs slip knot technique for each of our interrupted sutures so that the tension may be adjusted on each suture and there will be better regulation of postoperative astigmatism. We throw the Þrst two knots in the same direction in order to create the slip and do not secure the knots with two additional passes until the Þrst eight interrupted sutures are passed. The second 10-0 nylon suture is placed 180¡ away in the 6 oÕclock meridian, and is most crucial in terms of tissue alignment and postoperative astigmatism. An equal amount of tissue should be distributed on either side of the 6 and 12 oÕclock sutures. The three and 9 oÕclock sutures are then passed in the same fashion.

The authors prefer to pass four additional 10-0 nylon sutures between the four cardinal sutures in the same interrupted slip knot fashion. Again, the Þrst two throws are completed to create the slip and the knot is not secured. We then adjust the tension on each slip knot for the Þrst eight sutures passed in order to equalize tension around the cornea. When we have achieved equal tension, we secure each knot starting at the 12 oÕclock suture and proceeding in a clockwise direction until all eight knots are secured. An additional two single loops are made with each suture to secure the slip knot. Finally, the anterior chamber is Þlled with BSS to deepen it and to ensure a watertight wound closure.

4.1.6.9 Completion of Suturing

We prefer to pass an additional 16 radial, interrupted 10-0 nylon sutures to approximate the tissue, but not too tightly as to create unwanted astigmatism. These slipknots are secured after the passage of each suture. Throughout the suturing process, the anterior chamber is reformed with BSS to maintain a prolate shape to the donor cornea and viscoelastic is maintained on the donor cornea to protect the epithelium. A wet cellulose sponge should be kept on the corneal surface as well to avoid light toxicity from the operating microscope.

double running sutures, all of which are valid approaches to wound closure. A study compared the effect of three suturing techniques, including interrupted, single running, and combined interrupted and running, in KCN [4]. Post-keratoplasty astigmatism and Þnal BCVA were evaluated in 103 eyes where patients with a previous diagnosis of KCN underwent PK with one of the three suturing techniques [4]. No difference in the evaluated perimeters was detected among suture techniques [4].

Despite the technique the surgeon chooses, the most common error in any type of suture placement is tying a suture too tight. It is hard to resist tying a suture tightly as the surgeon often believes it will better ensure a watertight closure. But a tight suture is associated with many undesirable effects including cheese wiring, surface healing problems, ßat corneal curvature and hyperopia, and severe astigmatism [1]. It is thus essential that the sutures not be tied too tightly.

Another problem encountered in suture placement is that the surgeon does not bury the knots. Young cornea surgeons often leave knots unburied in the rush to complete the procedure and these knots can present a lot of problems. First of all, an exposed knot is a source of irritation and discomfort for the patient. Unburied knots are also associated with giant papillary conjunctivitis and infection. The cornea surgeon should be sure that all knots are rotated and buried at the end of the case. Care also should be taken that the knot is not rotated into the graftÐhost junction as scarring in this area will make the suture especially difÞcult to remove in the future.

4.1.6.11 Subconjunctival Medications

Subconjunctival injections of an antibiotic and a steroid are administered at the end of the case. Cefazolin, gentamicin, and dexamethasone are examples. A drop of an antibiotic such as Vigamox (Alcon) or Zymar (Allergan) is placed on the eye. Any remaining viscoelastic is placed on the cornea.

4.1.6.10 Suture Techniques

A variety of suture techniques exist. These include interrupted sutures only, running suture only, combined interrupted and running suture techniques, and

4.1.7 Intraoperative Complications

The most feared complication that can occur during PK is an expulsive choroidal hemorrhage. This will be discussed momentarily. LetÕs Þrst focus on some of the more common complications that occur and how to

deal with them. We have already mentioned shallowing of the anterior chamber with bulging of the anterior segment contents. This may not really be considered a complication, but it is a common occurrence and the surgeon performing cornea transplantation must know how to deal with it. Oftentimes, a diuretic such as mannitol given preoperatively can help decompress the vitreous cavity and decrease the incidence of anterior chamber shallowing. We see the anterior chamber shallowing most often when the host cornea is being removed with the beveled scissors. The surgeon inadvertently puts pressure on the globe. When shallowing of the anterior chamber occurs, the surgeon should Þrst be sure he/she is not applying any pressure to the eye. As previously mentioned, the patient may be placed in the reverse trendelenburg position and/or the lid speculum may be loosened. Viscoelastics can be used to push back bulging anterior segment contents as well, but care must be taken not to put too much viscoelastic into the anterior chamber as this may cause a rise in the immediate postoperative IOP.

Other intraoperative complications include scleral perforation with Þxation sutures, damaged donor buttons, and iris-lens damage [1]. When cataract extraction is combined with PK, the posterior capsule may be torn. Vitreous loss may occur in an eye that has had a previous cataract removal, and Þnally anterior chamber hemorrhage may occur in an inßamed or perforated eye from iris vessel leakage [1].

4.1.7.1 Scleral Perforation

The surgeon may inadvertently perforate the sclera with passage of the suture to secure the scleral Þxation ring. This can result in a retinal hole and subsequent retinal detachment. The ciliary body may also be damaged and hemorrhage may occur in the angle [1]. The surgeon sewing a scleral ring should always use a rounded rather than a cutting needle and keep in mind where the suture is being placed and how thin the sclera is.

4.1.7.2 Damage to the Donor Button

The donor cornea button can be damaged during trephination if an incomplete trephination occurs and the surgeon attempts to trephine again. Endothelial cell damage may also occur if the surgeon inadvertently touches the endothelium or drops the cornea during

transfer, or if the endothelium comes into contact with bulging anterior segment contents during suture placement. The surgeon should always be mindful of the endothelium and perhaps use a drop of viscoelastic on the endothelial surface for protection. The donor cornea should always be prepared prior to removal of the host cornea to ensure tissue is available for replacement, and the host cornea once removed should always be retained in BSS on the operative stand should something unexpected happen to the donor and the surgeon would emergently need to replace the patientÕs cornea.

4.1.7.3 Damage to the Iris-Lens Diaphragm

Damage to the iris-lens diaphragm usually occurs during trephination or with removal of the host cornea button. A bulging iris can be caught in the tip of the surgeonÕs scissors and the surgeon must always be mindful of this when removing the host cornea. Viscoelastic is used to push the iris back prior to the initial entry into the anterior chamber and the tip of the scissors is kept pointing up during the removal of the host cornea. Upward pressure is applied as the scissors are advanced around the perimetry of the cornea.

The lens may bulge and in a phakic patient, the anterior lens capsule may be damaged. The surgeon should be prepared to do a cataract extraction if needed and should consider having lens calculations available on phakic patients when going to the OR. Damage to the anterior lens capsule is a rare complication if the surgeon is careful.

4.1.7.4 Posterior Capsule Rupture

A torn posterior capsule may occur during removal of a cataract at the time of PK. The surgeon must be prepared to perform an anterior vitrectomy and place a lens implant in the sulcus or suture it to the iris or sclera. A backup intraocular lens of the correct power should be chosen for each of these locations and made available should they be needed.

4.1.7.5 Vitreous Loss

Vitreous loss may occur in patients with a history of cataract extraction when the posterior capsule was violated, and it may occur in aphakic patients as well. The