Tutorial
Introduction
Evolution of EK        Techniques
Surgical        Technique
Visual and        Refractive        Outcomes
Conclusion
References

Video

Endothelial Keratoplasty

· Frank W. Price Jr., MD · Marianne O. Price, PhD

Introduction

New lamellar techniques for replacing damaged or diseased corneal endothelium are rapidly improving transplant outcomes and reducing the surgical risks for patients with endothelial dysfunction.¹ These new techniques are revolutionary, considering how little corneal transplantation techniques have changed over the past 30 years, with prior advances including the introduction of the operating microscope, small-diameter monofilament suture and topical corticosteroids (to prevent immunologic graft rejection).

Endothelial keratoplasty (EK) retains healthy portions of a patient's cornea while replacing diseased endothelium with healthy donor tissue through a 5-mm incision. Its advantages compared to standard penetrating keratoplasty (PK) include the following²:

1. The recipient cornea remains structurally intact and resistant to injury.
2. Suture-related issues, including questions about placement method and concerns about late wound dehiscence, are eliminated.
3. The risk of expulsive intraoperative suprachoroidal hemorrhage is virtually eliminated with the small-incision technique.
4. Corneal innervation is retained, minimizing the risk of postoperative ocular surface disease.
5. Vision is recovered in a matter of weeks.
6. Visual fluctuations are minimal during the healing process.
7. The preoperative refractive status of the eye is essentially retained.

Corneal surgeons often have patients who have fallen and broken open an eye, sometimes many years after the transplant. This is especially tragic if a patient ends up losing the eye due to suprachoroidal hemorrhage. A PK wound never heals to become as strong as virgin cornea, and patients who undergo PK are at increased risk of traumatic injury for the remainder of their lives.³ EK makes it possible to transplant corneal endothelium through a small beveled incision similar to that used in cataract surgery, leaving the eye much stronger.

Evolution of EK Techniques

EK techniques continue to improve with important contributions from various surgeons. Melles and colleagues⁴ pioneered a number of the key elements. The original technique, called posterior lamellar keratoplasty (PLK), consisted of manually dissecting the recipient and donor corneas at 80% to 90% depth using curved blades, then excising the posterior recipient stroma and endothelium with small curved scissors and trephine. Melles and colleagues⁵ originally implanted the donor tissue through a 9-mm incision using a spatula, but later demonstrated that the donor tissue could be folded for insertion through a 5-mm scleral tunnel incision. Terry and Ousley⁶ developed a line of instruments and renamed the procedure deep lamellar EK (DLEK).

Melles and researchers⁷ later described a technique for stripping Descemet's membrane and dysfunctional endothelium from a patient. Descemet's stripping with EK (DSEK) is potentially less traumatic to anterior chamber structures than recipient lamellar dissection and tissue excision with trephine and scissors.¹ However, the authors initially found donor tissue attachment to be more challenging with DSEK than with PLK/DLEK, because the recipient stromal surface exposed by stripping Descemet's membrane is smoother than a hand-dissected surface. Using techniques to remove fluid from the donor/recipient graft interface,⁸ the authors have reduced the incidence of donor tissue dislocation to 1%.

Additionally, the authors have found that EK may be performed without stripping Descemet's membrane to restore clarity to failed penetrating grafts when Descemet's has no guttata, opacities or other abnormalities.⁹

Gorovoy, Goosey, Aronsky and others have popularized the use of a mechanical microkeratome to simplify the donor tissue dissection, a technique known as Descemet's stripping with automated EK (DSAEK). However, microkeratomes are an expense that some corneal surgeons cannot justify, so several eye banks now supply predissected donor tissue for EK. Femtosecond lasers are also being evaluated for donor tissue dissection.

Current EK techniques already offer substantial benefits for treating endothelial dysfunction, compared with traditional PK, and further improvements are expected as more surgeons perform the procedure and contribute their ideas. For example, a number of surgeons are trying to develop inserters that would allow the donor tissue to be implanted through a smaller incision.

Surgical Technique

The accompanying narrated video describes the EK surgical technique and illustrates how to dissect the donor tissue either by hand or with a mechanical microkeratome.

Video 1

Video 2

Video 3

Surgical pearls

EK is performed with topical or local anesthesia using either a retrobulbar or peribulbar block. The authors' preferred method is topical anesthesia. When a block is used, it is important to ensure there is no backpressure from periorbital swelling because that could lead to rapid and forceful shallowing of the anterior chamber while the donor tissue is being inserted or even push the donor tissue back out, in extreme cases.

The authors first prepare the donor tissue and ascertain that it is suitable for EK before making an incision on the patient's eye. Their preferred wound construction is a 5-mm scleral tunnel incision, because a scleral tunnel closes rapidly in the event of a complication, such as a patient coughing or a suprachoroidal hemorrhage.⁸ The ability to rapidly close the eye is an advantage of EK, as compared with PK. A clear corneal incision is also used. Temporal placement of the incision has several advantages. It preserves the superior conjunctiva for future glaucoma surgery, if ever needed and provides easier access to the eye than a superior approach, where the surgeon may have to contend with orbital anatomy in patients with large brows or sunken globes. It also facilitates donor tissue insertion because the corneal diameter is longer horizontally.⁸

The authors recommend injection of VisionBlue (DORC International, Zuidland, Netherlands) after scoring and before stripping Descemet's membrane. This trypan blue formulation stains exposed areas of Descemet's membrane and facilitates visualization of the membrane and the scored edge. The improved visualization is particularly helpful when the cornea is cloudy or hazy or when Descemet's membrane fragments during the stripping procedure.

After implanting and unfolding the donor button, removing fluid from the donor/recipient graft interface while the anterior chamber is filled with air helps ensure donor tissue adherence.⁸ The donor button is initially lifted and pressed against the recipient cornea with air for a few minutes until the natural pumping action of the donor endothelial cells creates sufficient suction to attach the donor to the recipient. However, fluid in the interface prevents strong attachment and allows the donor tissue to dislocate. The authors developed two techniques to remove trapped fluid while the anterior chamber is filled with air, and they recommend that both techniques be used in combination. First, a Lindstrom LASIK flap roller or comparable instrument is used to massage interface fluid from the center to the periphery where it can escape from underneath the donor button into the anterior chamber.⁸ This is done in all directions. Then, the authors make four small incisions in the mid-peripheral recipient cornea down to the graft interface.⁸ This releases additional fluid in approximately 15% of cases, even when the view through the operating microscope suggests that the donor is already in perfect apposition to the recipient. The combination of these two techniques has reduced the donor detachment rate to less than 1%. Dislocated donor tissue is reattached by injecting another air bubble using standard sterile technique in a minor surgery room.

Combined procedures

EK combines with other intraocular surgeries such as phacoemulsification, anterior vitrectomy, IOL exchange or secondary lens implant.⁸ However, the authors prefer to perform the other procedures beforehand as separate surgeries. EK is a longer surgery and, many times, these other surgeries are best performed with a different incision size. Performing cataract surgery before EK represents a paradigm shift from what is traditionally done with PK.⁸ Cataract surgery is usually performed after PK to help address the inevitable anisometropia and astigmatism, but that is not a concern with EK because it is refractive neutral. Furthermore, removing a cataract ahead of time provides a deeper anterior chamber and more room to insert and manipulate the EK donor tissue.^8,11 When phacoemulsification is combined with EK, the newly implanted IOL is still somewhat loose in the capsular bag and the bag or IOL can catch on the donor tissue during donor implantation.

Eyes should be carefully examined before EK so that any anterior membrane dystrophy is treated at the time of transplant, for example, with superficial keratectomy (SK).⁸ Additionally, SK is useful for removing cloudy epithelium to provide a clearer view into the eye. This is helpful when EK is combined with phacoemulsification/IOL implantation.

Visual and Refractive Outcomes

EK is refractive neutral, an important benefit to a patient, compared with PK. Outcomes from the authors' initial consecutive series using hand- or microkeratome-dissected donor tissue (100 cases each)¹² showed that postoperative mean refractive cylinder was unchanged from the preoperative value. Likewise, mean spherical equivalent refraction was unchanged when donor tissue was dissected with a microkeratome (Moria CB), whereas manual donor dissection resulted in a small 0.6 D hyperopic shift.

Visual recovery was accelerated with use of microkeratome-dissected donor tissue. One month after surgery, eyes receiving microkeratome-dissected tissue averaged one line better best spectacle-corrected visual acuity (BSCVA) compared with eyes receiving hand-dissected tissue, a statistically significant difference.¹² Six months postoperatively, 72% of the eyes with microkeratome-dissected donor tissue had BSCVA of 20/40 or better. Among those with no documented retinal or amblyopia problems, 80% saw 20/40 or better. These visual outcomes are better than those reported in large PK series for treatment of Fuchs' dystrophy and bullous keratopathy.^10,13-15 Furthermore, after EK, vision does not fluctuate substantially and hard lenses are not required for best vision, as they sometimes are after PK.^10,13

After EK, many patients with Fuchs' dystrophy report a greater improvement in their ability to read, drive and function in bright light or glare than is indicated by the change in their Snellen acuity score, which is measured in a darkened room. Consequently, it is not unusual for patients who have undergone EK to request surgery on their second eye within a month of having surgery performed on the first eye,¹ unlike patients treated with PK, who may never want to have surgery performed on their second eye.

Conclusion

EK has similar advantages over standard PK as phacoemulsification has over intracapsular surgery: The eye is left stronger and markedly more resistant to injury, and visual recovery is quicker. For most patients, the overall quality of vision is better after EK compared to standard PK. Corneal surgeons have patients with excellent visual acuity after PK, as well as those patients who have issues from high or irregular astigmatism,^10,13 or who have lost eyes from wound rupture caused by minor trauma.³ EK is refractive neutral¹ and allows an eye to better withstand minor trauma.

A further advantage of EK is that corneal innervation is retained and corneal sutures are not required,⁸ so complications with postoperative ocular surface disease should be minimal. In contrast, the authors' analysis of 4,000 PK outcomes indicated that ocular surface disease was the most common cause of PK failure in the early postoperative period.¹⁶

EK is now the authors' technique of choice for treating endothelial disorders such as Fuchs' dystrophy or pseudophakic bullous keratopathy. Procedural refinements have reduced the learning curve for the surgeon. EK requires different skills than PK, and surgeons beginning this procedure are encouraged to take an instructional course to provide patients with the best possible outcomes.

References

1. Price FW Jr., Price MO. Descemet's stripping with endothelial keratoplasty in 50 eyes: A refractive neutral cornea transplant. J Refract Surg. 2005;21:339-345.
   
   
2. Price FW Jr. Corneal transplantation as a refractive surgical procedure. J Refract Surg. 2005;21:216-217.
   
   
3. Elder MJ, Stack RR. Globe rupture following penetrating keratoplasty: How often, why, and what can we do to prevent it? Cornea. 2004;23:776-780.
   
   
4. Melles GR, Eggink FA, Lander F, et al. A surgical technique for posterior lamellar keratoplasty. Cornea. 1998;17:618-626.
   
   
5. Melles GR, Lander F, Nieuwendaal C. Sutureless, posterior lamellar keratoplasty: A case report of a modified technique. Cornea. 2002;21:325-327.
   
   
6. Terry MA, Ousley PJ. Deep lamellar endothelial keratoplasty visual acuity, astigmatism, and endothelial survival in a large prospective series. Ophthalmology. 2005;112:1541-1548.
   
   
7. Melles GR, Wijdh RH, Nieuwendaal CP. A technique to excise the Descemet membrane from a recipient cornea (descemetorhexis). Cornea. 2004;23:286-288.
   
   
8. Price FW Jr., Price MO. Descemet's stripping with endothelial keratoplasty (DSEK) in 200 eyes: Early challenges and techniques to promote donor adherence. J Cataract Refract Surg. 2006;32:411-418.
   
   
9. Price FW Jr., Price MO. Penetrating keratoplasty to restore clarity to a failed penetrating graft. Cornea. 2006; in press.
   
   
10. Pineros O, Cohen EJ, Rapuano CJ, Laibson PR. Long-term results after penetrating keratoplasty for Fuchs' endothelial dystrophy. Arch Ophthalmol. 1996;114:15-18.
    
    
11. Price MO, Price FW Jr. Cataract progression and treatment following posterior lamellar keratoplasty. J Cataract Refract Surg. 2004;30:1310-1315.
    
    
12. Price MO, Price FW Jr. Descemet's Stripping with Endothelial Keratoplasty (DSEK): Comparative Outcomes with Microkeratome- and Manually-Dissected Donor Tissue. Ophthalmology. 2006; in press.
    
    
13. Price FW Jr., Whitson WE, Marks RG. Progression of visual acuity after penetrating keratoplasty. Ophthalmology. 1991;98:1177-1185.
    
    
14. Claesson M, Armitage WJ, Fagerholm P, Stenevi U. Visual outcome in corneal grafts: A preliminary analysis of the Swedish Corneal Transplant Register. Br J Ophthalmol. 2002;86:174-180.
    
    
15. Williams KA, Hornsby NB, Bartlett CM, et al, eds. The Australian Corneal Graft Registry 2004 Report. Bedford Park, Australia: AGCR Publications; 2004:154.
    
    
16. Thompson RW, Price MO, Bowers PJ, Price FW Jr. Long-term graft survival after penetrating keratoplasty. Ophthalmology. 2003;110:1396-1402.