4.2.2.1 Donor Cornea Preparation

The technique of donor cornea preparation has been described by Price and Price [10]. In manual donor dissection, a corneoscleral rim is mounted on an artiÞcial anterior chamber (AC) and the chamber is inßated with air or BSS. The tissue is dissected at about 90% stromal depth using a series of three curved blades (DORC International, Zuidland, The Netherlands) [10]. Automated dissection is performed using a Moria CB microkeratome (Moria, Doyleston, PA) and either a 300or a 350-mm head depending on central corneal pachymetry less than or greater than 570-mm [10]. After dissection, the donor is transferred to a cutting block and placed endothelial side up. An 8-, 8.5-, or 9-mm-diameter trephine is used to punch a central corneal button. The button is maintained on the cutting block and covered until ready for use.

4.2.2.2 Host Cornea Preparation

The patient is brought to the operating suite after informed consent has been obtained. Anesthesia is a retrobulbar block (RBB) in most cases. The surgery may be performed under topical monitored anesthesia as well [9]. Attention is directed temporally on the patient and an 8-, 8.5-, or 9 mm trephine is used to mark the recipient corneal epithelium to outline the area from which DescemetÕs membrane is to be removed. Typically the same trephine needed for donor preparation is used. A paracentesis site is made temporally on the recipient with a paracentesis blade. Additional paracenteses are placed around the limbus at locations that will permit the entry of instruments to allow adjustment of the donor graft following placement. The gentian violet marker is used to mark the paracentesis blade so as to make identiÞcation of the paracenteses easy. The anterior chamber is Þlled with viscoelastic (Healon, Advanced Medical Optics, Irvine, CA) to deepen and maintain it. A 5-mm clear corneal temporal incision is made, or a scleral tunnel of the same length is created to minimize induced astigmatism. DescemetÕs membrane is scored along the previously marked epithelial tract using a modiÞed Sinskey hook. DescemetÕs membrane and endothelium are removed from within the scored area using a DescemetÕs stripping instrument to loosen the membrane in the 3 oÕclock position and pull it toward the incision at the 9 oÕclock position. The peeled DescemetÕs membrane is removed from the eye and

laid out across the cornea to ensure it was removed in entirety. The irrigation/aspiration handpiece is then used to remove the remaining viscoelastic from the anterior chamber so that the graft will adhere well.

4.2.2.3 Insertion of the Donor Cornea

The donor cornea is brought onto the operative Þeld on the cutting block and a small amount of Healon is placed on the endothelial surface to protect the endothelium during the folding process. The donor tissue is folded using a forceps (Kelman-McPherson [Katena], Goosey [Moria], or Charlie [Bausch & Lomb]), or any of the surgeonÕs choice into a taco or a burrito shaped conÞguration. The cornea cap is discarded. The edge of the 5 mm cornea or scleral incision is grasped and lifted with a toothed forcep to aid insertion of the tissue. The tissue is inserted into the AC stromal side up and air is injected through the paracentesis to unfold the donor tissue and press it up against the recipient cornea. The cornea/scleral incision is sutured with 10-0 nylon suture, and the knots are buried. If needed, a 27or 30-gauge needle with the tip bent with the needle holder and on a tuberculin syringe, can be inserted into the AC to aid proper positioning of the donor tissue. Care is taken to only grasp the stromal edge of the tissue so as to not damage any endothelial cells. When the surgeon is happy with the placement of the graft, the AC is Þlled with air for 10 min, followed by an exchange of air for BSS. Enough air is maintained in the AC so as to clear the inferior pupil when the patient is in an upright position. A drop of Vigamox (Alcon, Fort Worth, TX) is instilled in the eye. The patient is taken to the recovery room and will lay face up in the recovery room for 30 min to 2 h in order to allow the air to be in contact with the donor cornea and further promote adhesion. We prefer 2 h.

4.2.3 Postoperative Medications

Postoperatively, the authors prefer a combination of topical steroid and cyclosporin A as described earlier for PK. In general, topical prednisolone is prescribed 4Ð8 times daily for an average of 2Ð3 months postoperatively. The prednisolone is tapered by one drop per month until a dose of once daily is obtained. At that time, if the patient is phakic and has experienced no

rejection episodes or developed an IOP steroid response, the topical steroid is changed to loteprednol (Lotemax, Bausch & Lomb, Tampa, FL) one to two times per day. The patient is maintained on a minimum of one drop per day for at least 1 year. All patients receive topical cyclosporine A (Restasis, Allergan, Irvine, CA) twice a day for at least 1 year postoperatively. Many patients may remain on topical immunosuppressive medication for an indeÞnite time period.

4.2.4 Donor Dislocation Risks

Graft dislocation is a complication of DSEK. It is known as the most common postoperative challenge [11]. The incidence of donor detachment of the graft typically is higher when the surgeon performs his or her Þrst DSEK cases. Price and Price described their experience with donor dislocation in the Þrst 200 eyes in which they performed DSEK [11]. The rate of donor dislocation decreased inversely with the number of cases performed [11]. Others have cited similar results with dislocation rates in the literature ranging anywhere from 1 to 25% and higher [11Ð13]. Risk factors for graft dislocation include the entrapment of ßuid between the donor and recipient corneas and rubbing the eye [9]. Techniques to reduce interface ßuid have been described by Price and Terry and include the placement of fenestrations in the mid-peripheral recipient cornea to provide a pathway for ßuid to exit, the use of a LASIK roller to massage the corneal surface to facilitate removal of entrapped ßuid, and scraping the peripheral recipient cornea bed to allow for donor edge adhesion [9]. OÕbrien et al. reported that donor dislocation after DSEK is more common in eyes without an intact lens/iris diaphragm, and/or that underwent extensive tissue manipulation during surgery [12].

4.2.5 Repositioning Donor Tissue

When a clear space can be detected on postoperative slit lamp exam between the donor and recipient tissue, the donor graft has become detached from the recipient. Most donor dislocations are noted within the Þrst week to several weeks following surgery [11, 13]. Stromal edema is visualized over the area of dislocation and the patientÕs vision is often decreased from expected. It is

necessary at this point to reattach the donor tissue. This may be performed in a minor surgery room. The patient is taken to the minor surgery room and laid ßat under the operating microscope. Using sterile technique and a 30-gauge needle on a tuberculin syringe, the AC is Þlled again with air in exchange for anterior chamber ßuid. The donor graft is pressed into approximation with the host stroma. The AC is maintained again at a 100% air Þll for 10 min. The air is then exchanged for BSS as described in the surgical technique above so that the air bubble in the AC will clear the inferior pupil border when the patient sits upright so as to prevent pupillary block. The patient is maintained in the face up position as described previously for 30 min to 2 h to allow good donorÐhost apposition.

4.2.6 Treatment of Rejection Episodes

Endothelial graft rejection is a concern with DSEK. Signs of immunologic rejection at the initial diagnosis include keratic precipitates, diffuse corneal edema, and a combination of both [14]. Epithelial and anterior stromal immunologic reactions are not a concern because these are not transplanted in DSEK [14]. If a rejection episode is conÞrmed or suspected, the patient is placed on topical prednisolone every 1 h while awake along with oral prednisone (1 mg/kg/ day). This dosing regimen is maintained for 1 week and if the rejection episode has been treated successfully, the topical steroid dose is tapered very slowly to four times per day and then maintained at this dosage over a 3Ð4-month period before tapering it down to a maintenance dose of one more drop per day than what the patient had been using when the rejection episode occurred. If the patient had been on topical loteprednol (Lotemax, Bausch & Lomb) at the time of the rejection episode, a switch is made to topical prednisolone and dosed as outlined above. When the patient has demonstrated adequate resolution of the rejection episode, and following the slow taper of prednisolone, the surgeon may choose to switch the patient back to loteprednol at a higher dosing frequency than was being used prior to development of the rejection episode. Topical loteprednol has advantages over prednisolone in a phakic patient in that it has not been cited in the literature to cause cataract. Loteprednol also has an associated lower incidence of an IOP rise. Holland showed an 8% risk of an IOP

increase in known steroid responders using prednisolone following cornea transplantation compared to a less than 1% increase in those known steroid responders using loteprednol.

Most cases of endothelial graft rejection clear. One study cited a 7% graft failure rate following a graft rejection episode. The patient can be successfully regrafted with DSEK [14].

4.2.7 Visual and Refractive Outcomes

The recovery of useful vision following DSEK occurs usually within weeks [15]. This is in contrast to traditional PK where it may take up to 12 months or longer to achieve a satisfactory visual acuity when large diameter PK is not used. As described in ÒPK,Ó post-PK astigmatism is the most common complication of the full-thickness transplant. As mentioned, PK is considered to be a two step procedure with the Þrst step being the actual cornea transplant itself, followed by a second step that involves correction of the resultant astigmatism. DSEK has been shown to be a Òrefractive neutralÓ cornea transplant [15]. Visual and refractive outcomes of the Þrst 50 cases of a single surgeon were analyzed and mean manifest cylinder as well as mean manifest spherical equivalent were unchanged from preoperative values [15]. Furthermore, at 6 months post DSEK, 62% of patients had ³ 20/40 BCVA and 76% had ³ 20/50 BCVA [15]. Koenig et al. reported a 6-month postoperative BCVA of 20/40 or better in 61.8% of their patients [16].

A hyperopic shift of less than 0.50D has been reported by Price and Price [11], while Koenig et al. reported a hyperopic shift of 1.19 ± 1.32D [16]. Our patients have experienced a hyperopic shift similar to that reported by Koenig. For this reason, when implanting an IOL for a concurrent cataract removal at the time of DSEK, the surgeon should consider implanting an IOL with a refractive error of −1D.

the trabecular meshwork. Air that Þlls the anterior chamber can block the pupil when the patient is in the supine position, but if the air bubble is such that it Þlls less than 50% of the chamber at the end of the procedure, when the patient sits up to eat or go to the bathroom, the air will be in mid-pupil position such that any supine position pupillary block will resolve. Taking care to leave only a 50% air Þll at the end of the case, and having the patient sit upright after 2 h and prior to going home, to ensure that the inferior border of the air bubble clears the inferior pupillary margin, can help prevent pupillary block. Air may also become trapped behind the pupil, shallowing the anterior chamber, and pressing the iris against the endothelium leading to pupillary block. Dilation of the pupil postoperatively with phenylephrine and cyclogyl can add additional protection against pupillary block. If a patient presents with pupillary block due to trapped air, dilating drops should be administered and the patient should be laid back to allow the air to ßoat into the anterior chamber. If this does not work, BSS can be injected into the anterior chamber at the slit lamp to deepen it and force the air from behind the iris. A Yag laser can also be used to make an iridotomy thus providing a channel for aqueous ßow and relieving pupillary block. If the iris has been opposed to the endothelium for an extended period, adhesions may begin to form and the patient may need to be taken back to the operating suite to break the adhesions and deepen the anterior chamber. This should be done immediately to lower the IOP and to preserve endothelial cells.

Central retinal artery occlusion is a rare complication of DSEK. Compression of the retinal vasculature from the high IOP produced during the initial adhesion of the graft with the air bubble is the cause.

As mentioned, graft failure rates reported in the literature range from 0 to 29% with those cases requiring surgical reattachment of a dislocated donor disc having a higher rate of endothelial failure [12].

Endothelial cell loss following DSEK has been reported at 34% at the 6-month postoperative exam and remains stable for the Þrst year [17].

Pupillary block is a potential complication of DSEK. A large amount of air in the anterior chamber can block the ßow of aqueous through the pupil and out

It has been well established that DSEK surgery can preserve and restore the normal recipient cornea, while providing excellent visual acuity within an acceptable

time frame. The avoidance of full-thickness cornea incisions and sutures is a great advantage. Wound dehiscence with expulsion of intraocular contents is not a risk following DSEK. DSEK is associated with itsÕ own complications however, and the cornea surgeon performing this procedure must be aware of how to deal with these potential complications. Fullthickness penetrating keratoplasty is no longer indicated for endothelial dysfunction. DSEK patients regain vision sooner, have minimal to no refractive shift postoperatively, and have an eye that is structurally more sound [9]. As with PK, the long-term success of DSEK will depend on an adequate number of viable endothelial cells in the donor corneal tissue. The most common cause of late PK graft failures is due to low endothelial cell counts [16]. The rapid visual recovery, low morbidity, and minimal effect on the anterior corneal curvature make DSEK the procedure of choice for endothelial dysfunction (Fig. 4.16a, b)

a

b

References

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