What's New in Corneal Transplant Surgery?

What's New in Corneal Transplant Surgery? New techniques and technologies are saving more eyes than ever. Here is a rundown of the different surgical options and subsequent  postoperative care. By Maynard L. Pohl, OD RELEASE DATE: JANUARY 2013 EXPIRATION DATE: JANUARY 1, 2016 GOAL STATEMENT: New techniques and technologies are saving more eyes than ever.  This article provides a rundown of the different surgical  options and subsequent postoperative care.

Dr. Pohl is the clinical director at Pacific Cataract & Laser Institute in Bellevue, Wash., an optometric consultation and ambulatory surgical center specializing in medical and surgical eyecare. He is an adjunct assistant professor at Pacific University College of Optometry and State University of New York College of Optometry, and a fellow of the American Academy of Optometry and a founding fellow of the Optometric Retina Society. He is a frequent lecturer and author on topics of ocular disease comanagement.

CREDIT STATEMENT:

This course is COPE approved for 1 hour of CE credit. COPE ID 36596-PO. Check with your local state licensing board to see if this counts toward your CE requirements for relicensure.

JOINT-SPONSORSHIP STATEMENT:

This continuing education course is joint-sponsored by the Pennsylvania College of Optometry.

DISCLOSURE STATEMENT:

The author has no financial relationships to disclose.

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We frequently see patients with corneal disorders who need corneal transplant surgery, but surprisingly few actually undergo the procedure. Of the 10 million people worldwide who suffer from infectious and inflammatory eye diseases that result in corneal scarring and loss of best-corrected vision, only 1% receive corneal transplants.¹ That's a rather poor showing in our efforts to combat the fourth leading cause of global blindness. Corneal disorders follow cataract, glaucoma and AMD—all eminently more treatable—in the rankings of vision-threatening diseases.²

Fortunately, in the United States, we have some of the best facilities and specialists needed to perform corneal transplants; about half of all such procedures take place in our country. But collectively, eye care practitioners even here in the US should make a more concerted effort to bring these life-changing interventions to more people. Newer technologies and less invasive surgical techniques can make that possible.

This article will provide an overview of the different corneal transplant surgeries, suitable candidates and recommended postoperative care.

1. Corneal edema after DSAEK as noted on anterior chamber analysis (left). Resolution of corneal edema after DSAEK as noted on anterior chamber analysis (right)

UNDERSTANDING CORNEAL TRANSPLANT SURGERY

Keratoconus (and other noninflammatory thinning disorders), pseudophakic bullous keratopathy and Fuchs' dystrophy are three main indications for corneal transplantation in the Western world. Asia and Africa have a higher prevalence of infectious keratitis, corneal scars, late-stage endothe-lial disease and allograft rejection, naturally as a consequence of inadequate (or underserved) medical and surgical eye care in such regions.

Corneal transplant procedures include standard full-thickness penetrating keratoplasty (PK), endothelial keratoplasty (EK), anterior lamellar keratoplasty (ALK) and keratoprostheses. The clinical indications may be visual, structural, therapeutic, cosmetic or a combination. An important preoperative consideration in corneal transplant surgery is timing, because vision may be worse for up to six months after surgery. Complicating factors include eyelid disorders, dry eye, surface and intraocular inflammation, poor IOP control, previous grafts and incisions.

Success can be defined as better vision, less pain, comfortable spectacle or contact lens wear, reduced glare and, most importantly, an improved quality of life. Optometrists play a key role in the meticulous comanagement of the patient's preoperative and postoperative care.

NEW TECHNIQUES AND TECHNOLOGIES

New developments in corneal transplant surgery include limbal stem cell transplantation, femtosecond lasers, anterior and posterior lamellar keratoplasties, keratoprostheses and biosynthetic corneas.

* Limbal stem cell transplantation. Stem cell research will help determine the best type of limbal stem cell to transplant, the best method to transfer cultured cells to the eye surface and measures to decrease the risk of rejection through immunosuppressive therapies. Patients with multiple graft failures or those considered high risk for rejection may benefit from this procedure, which is currently available through ongoing research in academic clinical centers.

* Femtosecond lasers are increasingly useful for specialized donor or recipient tissue preparation for PK and EK, and particularly lamellar dissections for ALK. Femtosecond lasers allow the surgeon to more precisely measure and shape corneal tissue in graft preparation. As the enhanced quality and affordability of such lasers increases the value of using such technology, more surgeons will gravitate toward using it routinely for their corneal surgery patients.

* Lamellar keratoplasty. This surgery involves techniques to transplant an individual layer of the cornea and is evolving into the preferred surgical method for corneal disease. By replacing only the abnormal layer with a donor graft, the cornea is more structurally intact.

In some cases of EK, such as Descemet's stripping automated endo-thelial keratoplasty (DSAEK) and Descemet's membrane endothelial keratoplasty (DMEK), lamellar ker-atoplasty can eliminate surface incisions. The procedure is sutureless, which helps avoid suture-related complications and surface irregularities, and results in faster wound healing, smoother topography and quicker and greater visual stability.

There is lower risk of endothelial rejection with ALK; deep anterior lamellar keratoplasty (DALK) and superficial anterior lamellar keratoplasty (SALK) will essentially become steroid-sparing surgeries.

* Posterior lamellar endothelial transplantation. Currently known as EK, cases may be further categorized as either DSAEK or DMEK. Both procedures preserve the anterior to posterior stromal cornea and thereby avoid surface irregularities, suture-related issues and wound-healing complications associated with PK. Patients with chronic corneal edema associated with Fuchs' dystrophy or pseudophakic bullous keratopathy comprise the vast majority of suitable candidates.

The 30- to 45-minute procedure may be performed alone or in combination with cataract surgery. Descemet's membrane is stripped and the peripheral posterior stroma scored to allow adhesion of the donor graft, which has been carefully sized by the surgeon through either manual dissection using a microkeratome (DSEK) or automated dissection using a femtosecond laser (DSAEK).

The graft in DSAEK and DSEK consists of posterior stroma, Des-cemet's membrane and endothelium and is approximately 150µm thick. In DMEK, a more technically challenging procedure, the graft is thinner and consists only of Descemet's membrane and endothelium—essentially a replacement of host with donor tissue. In both procedures, the donor endothelium is protected with viscoelastic as the delicate graft is carefully folded, inserted and centered in apposition to the host cornea. Sterile air is injected into the anterior chamber to promote attachment and stabilization of the graft, followed by wound closure and application of a pressure patch to complete the surgery. The typical follow-up requires a few more visits compared to cataract surgery and may even be daily from day one pending anterior chamber stabilization.

Postoperative comanagement involves looking for wound leaks, quantifying the percentage of air bubble in the anterior chamber, using a slit lamp to carefully look for graft separation by optic section, evaluating the degree of stroma edema, measuring IOP and ruling out pupillary block in patients with an air bubble in the eye. At the immediate post-op exam, visual acuity may be 20/200 or worse. Expect long-term gradual improvement even with mild interface haze present; by six months, the majority of patients see better than 20/40.

Does graft thickness affect vision outcome with posterior lamellar surgery? A recent evidence-based clinical study at the University of Erlangen-Nuremberg in Germany compared 38 DMEK to 35 DSAEK outcomes in a consecutive case series of patients treated for Fuchs' dystrophy or pseudophakic bullous keratopathy.³The results indicated that DMEK provided faster and more complete vision rehabilitation by six months, compared to DSAEK.³ However, there was no significant long-term difference in best-corrected visual acuity outcomes between DSAEK and DMEK.

2. Patient S/P: DALK at day one with a single running suture, appearing similar to PK.

* Anterior lamellar kerato-plasty (ALK). This category of procedures, which includes deep anterior lamellar keratoplasty (DALK), sometimes involves the big bubble technique—when sterile air is injected between the corneal stromal lamellae to dissect out the abnormal diseased anterior layer. After the diseased anterior layers have been removed, the carefully sized donor graft is sutured into position with either a single running or interrupted sutures, or a combination of the two.

Suitable candidates for DALK include patients with thinning disorders (such as keratoconus, pellucid marginal degeneration and Terrien's corneal degeneration), as well as patients with deeper stromal non-perforating corneal scars (such as trauma, post-corneal ulcer, herpetic disease with stromal involvement and shallow RK).

While poor lamellar candidates for DSAEK or DMEK include complex anterior reconstruction cases, phakic patients and angle closure glaucoma suspects, poor candidates for DALK include cases that involve both stromal and endothelial disease, hydrops in keratoconus, old scars through Descemet's membrane such as deep RK with prior perforation, complex anterior reconstruction cases and prior PK. Patients considering ALK should be educated regarding the better long-term endothelial results, the relative uncertainty of a successful lamellar procedure and the possibility of converting to a full-thickness PK should the lamel-lar approach prove to be unsuitable at the time of surgery.

The progressive decay of endo-thelial cell counts after full-thickness PK was clinically demonstrated in a study that revealed that 17% endothelial cell loss occurs by two months post-op and 67% by 10 years.^4,5Other published research on corneal graft survival confirmed that in PK, there is a 90% survival rate at five years and that rate progressively diminishes at 10 years and dramatically thereafter; however in DALK, there is a 99.3% survival rate at 10 years and only 11% endothelial cell loss from six months to 10 years on average.⁶ Therefore, this steroid-sparing lamellar surgery has distinct advantages and should be considered in suitable candidates.

Postoperative comanagement involves looking for a double anterior chamber (treated by the surgeon with anterior chamber air injection) and stromal edema. Expect long-term gradual visual improvement even in the presence of mild interface haze.

* Keratoprosthesis. Advances in surgical techniques, improvements in material design and a better understanding of the pathophysiology of immune rejection have allowed for the development of artificial corneas, or keratoprostheses. Patients with multiple graft failures or those who have a high risk of rejection (e.g., severe ocular cicatricial pemphigoid, Stevens-Johnson syndrome or severe chemical burns) are suitable candidates. The ideal keratoprosthesis would be inert and not rejected by the patient's immune system, quick to implant, maintain long-term clarity, be easy to examine and allow an excellent view of the retina, while being relatively inexpensive.

3. A collar button-shaped device consisting of a PMMA optic and a back plate which secures the the donor tissue in between (left). The Boston Keratoprosthesis sutured into the trephined host cornea, similar to PK (right).

The AlphaCor Artificial Cornea (Addition Technology Inc.) is a biocompatible, flexible, one-piece hydrogel implant with a porous periphery and a central optical element.^7,8 First implanted in Australia in 1998 and FDA approved in 2003, it requires a complex two-stage surgical procedure with meticulous aftercare to reduce the risk of inflammation and stromal melt.^7,8 Post-operative care is typically done by the corneal surgeon.

The Boston Type 1 Keratoprosthesis (Massachusetts Eye & Ear Infirmary), the most commonly used keratoprosthesis in the United States, has been under development since the 1960s.^9,10 The design and therapeutic management has gradually been perfected, and received FDA clearance in 1992.^9,10Implantation is a one-stage procedure using a donor cornea. A collar button-shaped device consisting of a PMMA optic and a back plate with the donor tissue clamped in between is sutured into the trephined host cornea, similar to PK. Postoperative care typically involves placement of a large-diameter, extended wear bandage soft contact lens, lifelong prophylactic antibiotic (vancomycin), and careful comanagement that includes regular follow-up with the surgeon.

It is essential for optometrists to stay abreast of the most recent advances in corneal transplant surgery. This knowledge can then be used to educate patients and guide their clinical care. As specialized corneal transplant techniques and available technologies are further developed, patients suffering from visual disability will increasingly benefit from the improved surgical expertise of corneal surgeons. Furthermore, development of sound inter-professional relationships between optometrists and skilled corneal specialists will ultimately benefit the overall care of the patient.

REFERENCES

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