A Change in the Corneal Transplant Paradigm

The advent of femtosecond (FS) laser technology has changed the landscape of modern corneal transplantation surgery. Laser corneal transplant surgery produces consistently excellent outcomes with numerous benefits for the patient, including a significantly shorter healing time, superior wound integrity, and lower levels of regular astigmatism.

Manual penetrating keratoplasty (PK) surgery is an inexact science historically plagued by its inherent unpredictability. Problems often encountered with manual techniques include graft/host-sizing disparity, a prolonged recovery time of up to 1 year, and high levels of irregular astigmatism and wound instability, among others. Utilization of the iFS Advanced Femtosecond Laser (Abbott Medical Optics, AMO, Santa Ana, Calif.) in my practice has
eliminated most of these elements due to the ability to produce precisely matching donor and
host shapes and enhance the healing wound interface. Manual PK surgery involves
creating a spherical wound on the recipient's eye using a trephine applied to the cornea. The surgeon then harvests a corneal button 0.25–0.50 mm larger from the donor
eye using a tissue punch. A perfect fit between the recipient and donor tissue is very rare, and the donor may be further misshapen due to the distorting tissue pressure applied
by the keratoplasty punch.

 

Personal Experience

In contrast, the femtosecond laser creates a precise, customized cut pattern for donor and recipient making use of 3 overlapping components: posterior sidecut, lamellar ring cut,
and anterior sidecut. We have found that the zigzag template has allowed for the best
clinical outcomes. We position the initiation of the posterior side cut component at a depth of 75 microns from the recipient endothelial surface. Patients are evaluated preop-
actively to determine sizing and pachymetry. The IntraLase-enabled keratoplasty (IEK) calculator (AMO) allows for the prediction of programmed laser cuts for both donor and recipient. On the day of surgery, patients are first brought to our refractive surgery center where IEK cuts are produced. Once in the OR, the laser cuts are separated with a Sinskey hook, the anterior chamber is entered with a diamond knife, and pathology excision completed with keratoplasty scissors. In a series of 14 consecutive keratoconus cases performed over a 1-year period with iFS zigzag patterning, we have documented visual rehabilitation at a 3- to 6-month period of follow-up. The series consisted of patients ranging in age from 22–62 with BSCVA range of CF–20/100. Three-month postop data reveals that 100% of cases were correctable to 20/40 or better with spectacles with 64% achieving
a correctable vision of 20/25 or better. More impressive has been the level of post-op astigmatism with more than 75% demonstrating 2.5 diopters or less of regular astigmatism.

Use of Femtosecond Laser

Using femtosecond laser technology, the corneal surgeon now has the ability to create a precision keratoplasty outline on the recipient, which is matched on the donor
eye. Donor tissue may be prepped intraoperatively by the surgeon or with participating eye banks possessing corresponding femtosecond laser technology. The surgeon can evalu-
ate the patient clinically and decide which pattern of laser cuts best suits the pathology under consideration. Laser cuts are precise and predictable, completely eliminating the guess work and unwanted surprises often encountered with manual keratoplasty techniques. PK performed with blade-free femtosecond technology offers patients a substantially shorter period of visual rehabilitation. When using manual PK methods, it is not unusual for a patient to take upward of a year before achieving sufficient healing and wound stability to allow
for manifest refraction or contact lens fitting. It is not unusual for patients to develop high degrees of irregular astigmatism due to unpredictable and poor wound healing. Femtosecond keratoplasty has made such issues a thing of the past. In IEK, precise matching of complex
donor and recipient tissue planes have allowed for accelerated healing. This allows for the removal of sutures as early as 6 weeks postoperatively with more than 75% of patients manifesting very acceptable levels of regular astigmatism measuring 2.5 D or less. IntraLase laser technology can also allow for safe astigmatism touch-ups for patients with higher levels of postop astigmatism. Using the anterior side cut setting of the IntraLase, the surgeon
can place AK arcuate incisions inside of the graft-host interface. Improvement in outcomes with femto PK can be attributed to precise tissue apposition, but such precision in matched tissue planes must be accompanied by a modification of suturing technique in order to allow the patient to achieve all of the benefits of this technology. The classical PK suturing directive made use of deep, tight bites made to ensure apposition of posterior corneal layers.

Such tight, deep suturing with un-even tension often leads to irregular astigmatism and prolonged visual recovery. The zigzag IntraLase template permits a “tongue and groove” effect between donor and recipient. When combined with a modification of the suture technique, the matching planes may be opposed without creating unwanted excessive tissue
tension. Suture passes are placed at the junction of the anterior side and lamellar ring cut and are tied with the Terry slipknot technique to allow for even tissue tension and
healing vectors throughout the graft-host interface. Compared to the traditional
vertical PK wound profile, the IntraLase zigzag template increases the length of the wound healing interface, yielding improved wound stability and rapid healing. To maximize clinical outcomes, attention to detail is paramount. In order to ensure an accurate foundation for the interlocking zigzag effect, I typically start the suturing process with the meticulous placement of 4 cardinal 8.0 silk suture passes, which are later substituted with 10-0 nylon. Proper
placement of these first 4 sutures will ensure appropriate opposition as the suturing process is completed. With this technology, we no longer need to give patients un-
predictable outcomes with lengthy rehabilitation, poor quality vision, and the inability to wear corrective lenses or glasses due to irregular astigmatism. The corneal surgeon who offers this state-of-the-art technology can now allow keratoplasty patients to achieve the kind of predictable and repeatable results that we have come to expect from the family of refractive surgical procedures.

 

Editors’ note: Dr. Fox is medical
director of the Cornea and Refractive
Surgery Practice of New York and the
Clarity/TLC Center in New Jersey.
He has no financial interests related to
this article.

Author
Dr. Fox

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