macular abnormalities, retinal disease, or optic nerve damage. Preexisting glaucoma or ocular inflammation should be controlled before transplantation is considered. Active keratitis or uveitis should be treated medically if possible, and ideally, the eye should remain quiet for several months before surgery. An inflamed eye at the time of surgery is associated with a higher incidence of postoperative complications, such as graft rejection and failure, glaucoma, and cystoid macular edema. For example, corneal perforations in an acutely inflamed eye should, if possible, be closed either with cyanoacrylate tissue adhesive (for a small perforation) or by means of a lamellar corneal graft in order to restore the integrity of the globe and allow the inflammation to subside. A visionrestoring transplant may then be undertaken at a later date. Fluorescein angiography or optical coherence tomography (OCT) can be helpful in detecting retinal problems such as cystoid macular edema and age-related macular degeneration. If the media are completely opaque, standard B-scan ultrasonography for evaluating the posterior segment or ultrasound biomicroscopy for evaluating the anterior segment may reveal problems that could affect the visual prognosis after transplant. A potential visual acuity meter, a laser interferometer, blue-field entoptic phenomenon testing, visual field testing, color discrimination, 2-points-of-light separation, and visually evoked cortical potentials may also help in preoperative assessment of the afferent system.

In general, deep corneal vascularization, ocular surface disease, active anterior segment inflammation, peripheral corneal thinning, previous graft failures, and increased intraocular pressure (IOP) worsen the prognosis following transplantation and thus influence the appropriateness of this procedure for the affected patient.

Penetrating Keratoplasty

Surgical Technique for Penetrating Keratoplasty

Preparation of donor cornea

Donor tissue is most commonly prepared by means of trephination. In this process, the previously excised corneoscleral donor tissue is centered, endothelial side up, in the concave well of a cuttingblock apparatus that approximates the cornea’s shape. Sharp disposable blades are vertically advanced along a guiding shaft to punch the button in a precise, crisp, guillotine fashion. Femtosecond laser technology allows for the creation of mushroom-shaped or inverted mushroom–shaped side incisions, top-hat configurations, and zigzag shapes. The new side configurations are touted as being able to produce faster wound healing, allow early suture removal, and create a stronger and more stable graft–host interface. At this point, however, there are no studies demonstrating the long-term clinical superiority of the shaped incisions.

Most surgeons size the donor button 0.25–0.50 mm larger than the diameter of the host corneal opening (eg, an 8.0-mm-diameter corneal button for a 7.5-mm wound). This size disparity may reduce postoperative glaucoma, enhance watertight wound closure, prevent peripheral anterior synechiae formation and excessive postoperative corneal flattening, and provide the recipient eye with more endothelial cells. In keratoconus, especially in eyes with high axial length, sizing the donor tissue to match the exact size of the wound may flatten the corneal contour and thereby reduce postoperative myopia.

Preparation of recipient eye

For preparation of the host bed, use of the traditional handheld trephine is still one of the most

common methods because it offers convenience and is low cost, requires only sharp disposable blades, and is simple in design. However, hand fixation and rotation may lead to tilting and irregularity of cut as well as to unanticipated anterior chamber entry. Corneal vacuum trephines offer improved accuracy and consistency of cut, depth control, disposability, and suture placement marking points and are relatively low cost. Disadvantages include outward beveling of the posterior corneal edges in deep trephination, slightly reduced visualization of the cornea during centration, and more complexity than with a traditional trephine. Femtosecond laser technology can also be used to prepare the host bed so it matches the shaped side incisions in the donor tissue. Difficulties encountered with the use of the femtosecond laser include limited accessibility, increased costs, and the possibility that the treatment must be performed at a different location or time from the rest of the procedure.

After completion of the trephination and excision of the diseased cornea, the donor corneal button is placed onto the recipient’s eye, endothelial side down. Use of viscoelastic material helps protect the donor endothelium during surgical manipulation, keeps the anterior chamber formed, and shields the iris while the donor button is being sutured into the wound.

Suture techniques

The donor button is initially secured with at least 4 interrupted cardinal sutures. The second cardinal suture is the most important because the potential for induction of astigmatism is greatest if the suture 180° from the first suture is not aligned accurately. Complete wound closure is achieved with interrupted sutures, 1 or 2 continuous sutures, or a combination. Many variables contribute to astigmatism, but the key to minimizing astigmatism while suturing is to avoid tissue torque and distortion, anterior wound override, and posterior wound gape and to tie the sutures with uniform tension.

The suture knots may be positioned in either donor or host tissue and are buried in the corneal stroma. Most cornea surgeons prefer deep partial-thickness corneal suture bites incorporating 95% of the donor’s and host’s relative corneal thickness to avoid posterior wound gape and facilitate wound stabilization and healing.

A variety of techniques are used to complete the suturing, depending on the clinical situation and surgeon preference. 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, in which wound healing is rapid. If they attract blood vessels or loosen because of wound contraction, sutures may be removed selectively after sufficient healing of the donor–recipient interface. 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, inflammation, or thinning, single or double continuous sutures or combined interrupted and continuous sutures (Fig 15-1) can be used to secure the PK. If properly placed, continuous sutures may allow more even distribution of tension and healing around the wound. The advantages of continuous sutures include the ability to adjust the suture intraoperatively or postoperatively using a keratometer and their ease of removal postoperatively. Disadvantages include sectoral loosening, or cheese wiring, which may compromise the entire closure.

Complications that can occur during PK include the following:

damage to the lens and/or iris from the trephine, scissors, or other instruments irregular trephination

inadequate vitrectomy resulting in vitreous contact with the graft endothelium poor graft centration on the host bed

excessive bleeding from the iris or wound edge (in vascularized host corneas) choroidal hemorrhage and effusion

iris incarceration in the wound

damage to the donor endothelium during trephination or handling

In severely edematous corneas, and in repeat PKs, the recipient Descemet membrane may be inadvertently left behind after corneal excision, as it is easily stripped completely from the stroma. Thus, the recipient eye must be carefully examined for retained Descemet membrane before the donor graft is placed.

Postoperative Care and Complications

The long-term success of a PK depends on the quality of postoperative care as much as on the performance of the operative technique. Routine postsurgical care—use of topical antibiotics, tapering topical corticosteroids, and frequent office visits—is directed at preventing and allowing early recognition of the myriad complications that can occur after PK, as well as optimizing postoperative wound healing and facilitating rapid vision rehabilitation. This section covers some of the more common postsurgical complications. Astigmatism and graft rejection are discussed separately.

Wound leak

The wound is always checked carefully for leakage at the end of surgery. Small wound leaks that do not cause anterior chamber shallowing frequently close spontaneously. Patching, therapeutic contact lenses, and use of aqueous production inhibitors may hasten wound closure. Resuturing is advised for leaks associated with shallow anterior chambers and low pressures lasting longer than 3 days.

Flat chamber or iris incarceration in the wound

Both flat chamber and iris incarceration in the wound imply either poor wound integrity or excessive posterior pressure. Early surgical intervention is advised.

Glaucoma

High IOP may occur at any time after PK. Often, the first clinical sign is the loss of folds in the Descemet membrane, which is usually seen in the early postoperative period. Glaucoma should be treated aggressively with medical, laser, or surgical intervention as indicated. Unusual causes include epithelial downgrowth and fibrous ingrowth. (See BCSC Section 10, Glaucoma.)

Endophthalmitis

After PK, endophthalmitis may arise from intraoperative contamination, donor button contamination, or postoperative invasion by organisms. Aggressive intervention can save the eye and vision in some cases. (See BCSC Section 9, Intraocular Inflammation and Uveitis.)

Primary endothelial failure (primary donor failure)

When a graft is edematous from the first postoperative day and remains so without inflammatory signs, a deficiency of donor endothelium is presumed (Fig 15-2). Most surgeons allow at least 4 weeks and up to 2 months for spontaneous resolution of edema before considering a regraft.

Figure 15-2 Primary endothelial failure after penetrating keratoplasty (PK).

Persistent epithelial defect

Large epithelial defects are common after PK, but they should heal within 14 days. After this time, irreversible scarring and ulceration may occur. Ocular surface disease (eg, dry eye, exposure, rosacea, blepharitis, trichiasis) should be ruled out or treated. Lubrication, patching, therapeutic contact lenses, punctal occlusion with plugs or cautery, and tarsorrhaphy may be helpful in difficult cases. (See Neurotrophic Keratopathy and Persistent Corneal Epithelial Defect in Chapter 3.) If these measures are not successful, herpetic keratitis (Fig 15-3) should be considered in the differential diagnosis, even in cases in which this was not the underlying reason for the graft. Oral antivirals may be used as a therapeutic trial.

Figure 15-3 Herpes simplex keratitis recurring in a graft.

Recurrence of primary disease

Bacterial, fungal, viral, and amebic keratitis can recur in a graft. Medical treatment directed at the causative agent in recurrent infections is the initial form of therapy. In patients with superficial recurrent corneal stromal dystrophies such as granular or lattice dystrophy, PTK can be used to remove visually significant lesions (Fig 15-4).

Figure 15-4 Recurrence of granular corneal dystrophy after corneal transplantation. (Courtesy of Robert W. Weisenthal, MD.)

Suture-related problems

Postoperative problems related to sutures include the following:

excessive tightness of the sutures, producing an irregular astigmatism

loosening (usually as a result of wound contraction, suture breakage, or suture cheese wiring) breakage of a continuous suture (Fig 15-5)

infectious abscesses (usually localized around loose, broken, or exposed sutures; Fig 15-6) noninfectious (toxic) suture infiltrates

giant papillary conjunctivitis from exposed knots vascularization along suture tracks

Figure 15-5 Broken continuous suture after PK. Removal is necessary to avoid further vascularization, infection, and graft

rejection. (Courtesy of Robert W. Weisenthal, MD.)

Figure 15-6 Suture abscess caused by Streptococcus pneumoniae, 2 years after PK.

Loose and broken sutures do not contribute to wound stability and, therefore, should be removed as soon as possible. Totally buried fragments of interrupted sutures may be left. Vascularization along the suture indicates that the wound is adequately healed in the vicinity and that sutures may be removed safely. Vascularized sutures are also prone to loosening and may increase the chance of graft rejection. If only a small segment of the continuous suture is eroded, it is possible to remove this portion while leaving the remainder intact, especially if there is minimal corneal astigmatism. Patients should be warned to return if a foreign-body sensation is noted, as contiguous portions of a continuous suture may loosen and erode at a later date. After the sutures are removed, there may be a dramatic shift in refractive error or astigmatism, so the patient should be seen for follow-up to ensure wound stability and to recheck refraction.

Microbial keratitis

The use of topical corticosteroids, the presence of epithelial defects or edema, and exposed sutures predispose the patient to infectious keratitis, sometimes caused by unusual organisms. Decreased corneal sensation and topical corticosteroid use may also delay presentation. Culture of the infiltrate and the exposed suture with initiation of broad-spectrum antibiotic therapy is necessary to avoid graft failure. A peculiar form of keratitis, infectious crystalline keratopathy (Fig 15-7), is seen in grafts and other immunocompromised corneas. Branching colonies of organisms proliferate in the deep corneal stroma with minimal or no inflammatory response. Many organisms have been implicated, but Streptococcus viridans is seen most frequently.