2.1 Introduction

Corneal surgery has a long history marked by periods of innovation as well as long stretches of relative inactivity. The Greek physician Galen (130–200 AD) was one of the first to document the removal of superficial corneal scars in what might be considered the first corneal surgery. However, corneal transplantation would not be attempted until the 1800s. The first corneal transplants attempted in humans were xenografts; however, for reasons well known to us today, these proved to be unsuccessful. Eduard Zirm performed the first successful corneal allograft in 1905 on a 45-year-old male who had sustained alkali burns to both corneas. Although this rudimentary surgery allowed the patient to return to work, the modern era of cornea transplantation became possible only with advancements in antiseptic principles, anesthesia techniques and pharmacology, development of the operating microscope, Paton’s work in the formation of the eye bank industry, and also improvement in suture technology, beginning in the mid-20th century. The 21st century has been marked by differentiation into anterior and posterior lamellar techniques, which has revolutionized the field of keratoplasty. The future of corneal transplantation will be limited by availability of donor tissue, especially in developing countries, and enhanced with better control of graft rejection and improved refractive outcomes. The development of femtosecond laser, as well as artificial, bioengineered, or three-dimensional-printed corneas may influence the future trajectory of corneal transplantation. ^{1 , 2 , 3 , 4}

2.2 Indications

Prior to the widespread use of lamellar techniques such as deep anterior lamellar keratoplasty (DALK) and Descemet’s membrane endothelial keratoplasty (DMEK), in which only the diseased portion of the cornea are removed, penetrating keratoplasty (PK) was the only procedure for indications such as keratoconus and Fuchs. Conditions such as Fuchs’ corneal dystrophy and pseudophakic corneal edema are now preferentially treated with posterior lamellar techniques such as Descemet’s stripping automated endothelial keratoplasty (DSAEK) and DMEK. Even cases of prior failed PK can be treated with posterior lamellar techniques. For anterior corneal disorders like superficial scars or keratoconus, in which the endothelial layer is often unaffected, anterior lamellar techniques such as DALK are common; however, in cases of failure to complete the DALK procedure, the surgeon may need to convert to a PK and therefore knowledge of this procedure is still mandatory. Currently, PK remains the procedure of choice when there is a combination of anterior and posterior corneal pathology. The major indications for PK include full-thickness corneal scars (due to trachoma, vitamin A deficiency, and infectious keratitis), but there is a geographic variation in the primary indications for PK. A recent systematic review revealed both chronological and regional variations in reported global PK indications. Specifically, prevailing reported indications for PK between 1980 and 2014 were keratoconus (Europe, Australia, the Middle East, Africa, and South America), pseudophakic bullous keratopathy/aphakic bullous keratopathy (North America), and keratitis (Asia). ⁵

2.3 Preoperative Considerations

There is inconclusive data regarding the role of prophylactic preoperative antibiotics. Prophylactic use of antibiotics is considered to be a risk for development of multidrug-resistant organisms, allergic reactions, and increasing cost.

Several studies have demonstrated the patient’s periocular flora to be the most common source of endophthalmitis. As such, preoperative management of blepharitis as well as intraoperative lid preparation are crucial. Any debris along the eyelid margin should be removed and care should be taken to adequately cover and retract the lashes out of the surgical field. A small Tegaderm cut in half, Steri-Strips, or an adapted surgical drape may be employed to this end.

2.4 Technique

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  The eye is prepared in standard sterile fashion. The eyelid speculum should be optimized to maximize exposure while minimizing tension on the globe, which may complicate trephination or affect suture placement (▶Fig. 2.1).

  
  
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  A scleral fixation ring may be placed to prevent scleral collapse in pediatric, aphakic, pseudophakic, or combination procedures. The diameter of the ring is sized to approximate the interpalpebral diameter, just inside the field delineated by the eyelid speculum. The ring is secured with four interrupted 8–0 Vicryl sutures placed at a partial scleral thickness depth. These sutures may be more comfortably passed from the periphery towards the limbus. While the ring should be securely fashioned to the sclera, it should be loose enough so that one could rotate it slightly employing a tying forceps (▶Fig. 2.2).

  
  
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  Mark the geometric center of the host cornea; one may use the center of the pupil to capture the optical axis, which is generally nasally displaced. A midway point may be chosen should the center of the cornea and optical axis notably differ in location.

  
  
  
  
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    Use calipers to measure the corneal diameter from the center extending horizontally and vertically to determine the appropriate size for host and donor trephine as well as to demarcate the proposed area on the host for trephination. Using gentle pressure, the trephine may be used on a dry corneal surface to demarcate the proposed area prior to trephination (▶Fig. 2.3a, b).

    
    
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    The indication for which the transplant is being performed may alter the desired centration of the graft. For example, in a patient with keratoconus, care must be taken to avoid trephination in an area of thinning as well as account for the potential inferonasal predilection for the apex of ectasia.

  
  
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  At this juncture, surgeon preference may dictate whether donor or host trephination is pursued. It is advantageous to prepare the donor cornea prior to trephination of the host to minimize the amount of time spent “open sky.”

  
  
  
  
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    Trephine the donor tissue, typically aiming for 0.25 or 0.5 mm larger than the planned host trephination; this allows for adequate apposition of tissue, minimizes tension on the wound, and minimizes narrowing of the anterior chamber angle. The exception is keratoconus and other ectatic disorders in which it is preferable to have an isometric graft (same size graft as the host trephination) to reduce myopia.

    
    
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    Trephination may be completed using a vacuumed or nonvacuumed trephine. Additionally, the femtosecond laser may be used to prepare both the donor and host tissues. However, this option is not very common due to its cost and availability factors (▶Fig. 2.4).

  
  
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  Once the donor cornea has been prepared, the host cornea is then trephined to near full-thickness depth; maintaining a perpendicular position of trephine to cornea will optimize the symmetry of the cut for 360°. A near full-thickness trephine provides an additional amount of control as the anterior chamber may then be entered using a sharp blade, avoiding an abrupt shift in intraocular pressure, reducing the risk of suprachoroidal hemorrhage. At this juncture, a miotic agent may be injected to constrict the pupil and protect the crystalline lens if no lens procedures are planned or have been previously completed. Additionally, injection of a dispersive viscoelastic into the anterior chamber will encourage both iris and lens to remain posterior while the host cornea is excised (▶Fig. 2.5).

  
  
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  The host corneal tissue is excised using curved corneal scissors. It is advisable to have both right and left curved scissors to enhance maneuverability. Scissor tips should be visualized at all times and slight upward pressure during cutting may reduce undue iris trauma (▶Fig. 2.6). Cuts made perpendicular to the host margin will reduce postoperative astigmatism, however cuts slightly beveled inwards may enhance a watertight seal by creating a posterior wound lip. It is also crucial to continue to refill the chamber with viscoelastic to prevent iris prolapse or trauma. Any remaining tissue tags may be judiciously removed (▶Fig. 2.7).

  
  
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  The donor graft is then carefully grasped at the junction of epithelium and stroma with fine-toothed, two-pronged forceps, avoiding any contact of endothelium. The donor is carefully secured to the host corneal tissue with an interrupted 10–0 nylon suture at the 12 o’clock position. The needle may be adjusted once secured within the needle driver to optimize angulation and promote radial suture placement.

  
  

  In order to get adequate depth bite of both tissues, it is helpful to approach the donor tissue nearly perpendicular with the needle emerging at the donor margin at about 90% depth. If necessary, the needle may be re-grasped prior to entering the host tissue similarly, just above the level of Descemet’s membrane. A wrinkle in Descemet’s membrane may be appreciated when the needle is at the recommended depth. The suture should enter the donor and emerge from the host equidistant from the wound. Interrupted suture may be tied using an initial triple loop followed by two additional single loops or a slip knot technique, which provides immediate stability to the wound while allowing for adjustment of tension as additional sutures are placed (▶Fig. 2.8).

  
  
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  The second suture is placed 180° away from the first at the 6 o’clock position. Accurate placement of this suture is crucial for proper tissue alignment and minimizing postoperative astigmatism. It should be placed so that tissue is distributed equally on each side. As the tissue is engaged entering the donor, a linear fold around the level of Descemet’s membrane emanating from the 12 o’clock suture running towards the 6 o’clock position suggests proper suture alignment. The suture placement may be further refined by rotating the inferior donor rim a few degrees in each direction prior to finishing the pass through the host. The suture is tied, the chamber is reformed, and if necessary, the suture may be replaced at that juncture or once the additional cardinal sutures have been placed (▶Fig. 2.9). To complete cardinal suture placement, the 3 o’clock suture followed by the 9 o’clock suture is placed and tied (▶Fig. 2.10).

  
  
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  It is essential to continue to refill the anterior chamber periodically as this maneuver eases proper suture placement and tension as well as decreases the risk of iris incarceration within the wound.

  
  
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  Generally, an additional 12 radial interrupted 10–0 nylon sutures and possibly a 10–0 nylon running suture with 90% stromal depth bites are placed to provide adequate wound apposition without gaping or override of tissue (▶Fig. 2.11a, b). The decision to use running versus interrupted sutures is largely one of the surgeon preferences; however, interrupted sutures should be preferentially used when there is significant inflammation and vascularization as sutures in these areas will loosen earlier than others and if they are interrupted, these sutures may be selectively removed without compromising the wound integrity elsewhere.

  
  
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  Once the sutures are at the desired tension, the ends are trimmed and rotated to bury the knots into either host or donor side, avoiding placement within the wound itself.

  
  
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  The wound is assessed with a cellulose sponge and/or fluorescein staining (▶Fig. 2.12). Leaks may be addressed by replacing the suture or placing additional 10–0 nylon interrupted suture to bolster weaker areas.

  
  
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  The scleral fixation ring is removed.

  
  
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  If there is concern for limbal stem cell deficiency, eyelid abnormalities, and/or neuropathic keratopathy, a medial and/or lateral tarsorrhaphy may be completed intraoperatively to enhance postoperative wound healing. Punctal occlusion, via punctal plugs or punctal cauterization, may be beneficial in these patients as well.

  
  
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  No consensus for perioperative steroid or antibiotic administration prevails at this juncture. Betadine is applied at the conclusion of the case followed by a combination antibiotic/steroid ointment. The eye is patched and shielded.