Penetrating Keratoplasty

From EyeWiki


Indications

  • Keratoconus and ectasias
  • Corneal degenerations
  • Corneal dystrophies including Fuchs endothelial dystrophy
  • Noninfectious ulcerative keratitis
  • Microbial keratits including Fungal and Bacterial keratitis
  • Viral keratitis
  • Post infectious keratitis
  • Congenital opacities
  • Chemical injuries
  • Mechanical trauma
  • Refractive indications
  • Regraft related to allograft rejection
  • Regraft unrelated to allograft rejection

Anesthesia Considerations

The choice of type of anesthesia for a penetrating keratoplasty depends on patient-specific factors and the surgeon's comfort levels. If a patient expresses anxiety and is likely to move around during the surgery, the surgeon may seriously consider general anesthesia. Alternatively, some ophthalmic centers routinely perform all penetrating keratoplasties with MAC and a peri- or retrobulbar block. In these cases, it is crucial to perform adequate ocular massage after the block to minimize posterior pressure. Furthermore, the surgical team may consider additional measures to minimize posterior pressure such as a reverse Trendelenburg position or IV mannitol. Pediatric cases are typically always performed under general anesthesia.

Surgical Procedure

Before initiating the surgery, the surgeon should decide on the appropriate size of the corneal trephine and donor punch. Typically, a trephine is selected to encompass the entirety of the corneal pathology (e.g. in cases of microbial infections). Sometimes in the case of microbial keratitis, the infection extends beyond the limbus. In these cases, the surgeon may choose to perform a larger corneoscleral graft. In other extensive cases, such as with corneal dystrophies, corneal trephination may not include the entirety of the pathology. In these cases, a smaller graft can be used as long as it allows for the visual axis to be clear. The use a corneal button 0.25-0.50mm larger than the diameter of the host corneal opening is recommended as it can help reduce excessive postoperative corneal flattening, reduce the risk of secondary glaucoma, and enhance wound closure. In cases of keratoconus, some surgeons will opt to use a corneal button the same size as the host corneal trephination, in anticipation of potential future graft steepening.

After selecting the sizes of the trephine and punch, the following steps are performed:

  1. The initial step in penetrating keratoplasty should be the preparation and punch of the donor tissue. The epithelial side of the donor may be marked as well to guide suture placement. It is critical to prepare the donor tissue prior to entering the patient's eye, to be prepared for any need for urgent closure.
  2. The host cornea is entered with a paracentesis blade and the anterior chamber is filled with viscoelastic. Of note, some surgeons will fill the anterior chamber with viscoelastic after trephining the host cornea, without the need for a paracentesis.
  3. The host cornea is marked with an RK marker and trephined.
  4. The donor tissue is placed endothelial side down on the recipient's eye.
  5. The cornea is then sutured in place with either interrupted or continuous sutures. Interrupted sutures are preferred in vascularized, inflammed, or thinned corneas as well as in pediatric cases. Typically 16 sutures are placed, although in large corneal grafts or corneoscleral grafts, additional sutures may be necessary. Suture placement is usually performed to minimize the development of astigmatism, with every other suture being placed 180 degrees away from the previous suture. The first four cardinal sutures are placed at the 12:00, 3:00, 6:00, and 9:00 positions. Care must be taken so that each suture has equal tension compared to the other sutures.
  6. Prior to placement of the final 2 sutures, the viscoelastic is removed from the anterior chamber. Typically, balanced salt solution is injected at one opening in the graft host junction, with an additional cannula placed at the opposite graft host junction 180 degrees away to allow the viscoelastic to "burp" out of the anterior chamber.
  7. All sutures are rotated so that the knots are buried.
  8. Some surgeons may choose to use a fluorescein strip to assess for leakage at the graft host junction.
  9. Subconjunctival steroid and antibiotic are injected, the eye is patched, and a shield is placed.

Combined Procedures

Penetrating keratoplasty may be combined with cataract surgery, secondary intraocular lens implantation, glaucoma surgery, and retinal surgery. In cases of combined retinal surgery, often a temporary keratoprosthesis is sutured in place first to allow for the retina surgeon to visualize the posterior segment. After completion of the retinal surgery, the temporary keratoprosthesis is replaced with the permanent corneal graft.

Intraoperative Complications

  • Poor graft centration
  • Irregular trephination
  • Damage to the lens
  • Damage to the donor tissue
  • Choroidal hemorrhage and effusion
  • Incarceration of iris tissue in the wound
  • Vitreous in the anterior chamber

Postoperative Complications

Corneal Graft Rejection

Symptoms

  • Decreased vision, pain, redness and photophobia after a corneal transplant

Signs

  • Keratic precipitates or a white line on the corneal endothelium
  • Stromal edema or infiltrates
  • Subepithelial or epithelial edema
  • Conjunctival injection
  • Anterior chamber cells or flare
  • Neovascularization

Differential Diagnosis

  • Noncompliance with steroid drops
  • Increased intraocular pressure
  • Uveitis
  • Suture abscess
  • Corneal infection
  • Recurrent disease in the graft (e.g. herpetic or corneal dystrophy)

Treatment

  • Start a topical steroid, such as prednisolone acetate 1% q1hr immediately. Use a cycloplegic agent. Systemic steroids (prednisone 40-80 mg daily) should be considered in cases that do not respond to topical steroids and in recurrent rejection episodes. [1]

Additional Resources

References

  1. The Wills Eye Manual, 4th Edition. Kunimoto, Kanitkar, & Makar. Lippincott, 2004.
  1. H.E., Barron, L., McDonald, M.B., eds., The Cornea, 2d ed., 1996
  2. External Disease and Cornea, Section 8. Basic and Clinical Science Course, AAO, 2006.