Penetrating keratoplasty: Reinventing and refining tradition
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Suturing penetrating keratoplasties is tricky and worth mastering. My guest in this column is Roswell R. Pfister, MD, who explains the intricacies of this art.
Amar Agarwal, MS, FRCS, FRCOphth
OSN Complications Consult Editor
My reasons for writing this column are not to try to recreate the halcyon days of penetrating keratoplasty for all surgical corneal cases. Corneal surgery has moved on to the removal and replacement of specific diseased tissues using new sets of sophisticated techniques.
But when the only alternative is PK, it is therefore incumbent on all corneal surgeons to acquire the advanced skills necessary to perform this operation in its most productive way with the expectation of great success rather than an unsatisfactory outcome. Given the current distaste for PK, especially among younger corneal surgeons, it is my objective to dissuade this way of thinking by showing an innovative approach to suturing that solves old, bothersome problems.
Zigzag continuous suture
I have dubbed the cornerstone of this technique the zigzag continuous suture, a procedure I adopted soon after my fellowship with Claes Dohlman, MD, my esteemed mentor, who first introduced me to the concept of a continuous nylon closure technique using radially placed and longish sutures. From this initial exposure, I refined and reframed my technique into a different appearance and functionality. For a variety of reasons, continuous suturing of any kind has been supplanted by interrupted sutures in the U.S., although conventional continuous suturing is somewhat more popular in Europe.
There are five independent placements of the zigzag continuous suture controlling the quality of wound apposition: distance between sutures, depth of sutures, length of suture in donor and recipient, angle of insertion and the final tension in the suture. Failure to consistently and accurately control suture placement in any one of the five conditions might result in some shortcoming, perhaps total failure. The following is a breakdown of each of the five elements that play major roles in proper zigzag continuous suture placement.
Distance between sutures
There is no set distance between suture passes, but the number of suture passes in any quadrant will vary generally from four to five, depending on the size of the transplant and the quality and thickness of the cornea in each respective quadrant. Barring a full-thickness suture placement, a wound leak is most likely to occur between suture passes. The cause of a leak might be an excessive distance between passes or misplacement of one or both suture passes adjacent to the leak.
Depth of the suture
If sutures are placed either superficially or even in the mid stroma, the failure to achieve pre-Descemet’s placement results in a posterior gape of the wound, allowing aqueous humor to enter the gape and swell the stroma. The consequential stromal swelling might result in irreversible peripheral and sometimes central corneal edema of the donor. There is also less stromal apposition within the wound, resulting in a weaker wound. Superficial or mid-stromal suture placement enhances cheese-wiring, loosening of the suture and potential overriding of the donor, wound leaks and gross astigmatism. Remember that the two strongest portions of the wound postoperatively are at and just below Bowman’s layer anteriorly and just above and at Descemet’s membrane posteriorly. To avoid problems, the needle must enter the stroma of the donor almost vertically, passing the needle to pre-Descemet’s stroma, and then initiate a perpendicular turn to the wound, crossing the wound to enter the pre-Descemet’s recipient stroma. Drive the needle across the pre-Descemet’s stroma, turn the needle perpendicular again and exit the recipient.
Length of the suture
Place the suture 0.75 mm from the donor edge and 1.25 mm behind the recipient corneal edge. Donor cornea has strong and mature collagen, able to hold this length of suture without collapsing or cheese-wiring. The recipient cornea might be weaker and less stable, requiring a longer pass of the needle and suture for security.
Angle of insertion
The angle of the suture is one of the key elements of the zigzag continuous suture. The angle of suture placement, vis-à-vis the wound, varies depending on the conditions and quality of the recipient tissue in each eye. Firm, normal cornea allows suture angles to be somewhat more obtuse, with broader bases to the isosceles triangles. Thinner and/or softer recipient tissues demand more suture passes in each quadrant with correspondingly more acute angles. Be aware that the suture is being placed around a circle, hence the surgeon is continuously changing hand and needle angles to accommodate this change.
Tension of the suture
For the wound to be watertight, there must be sufficient tension in the suture to force closure of the wound without exerting excessive point or meridional tensions. Using a combination of the zigzag suture and the specially designed Pfister spatula ensures that the tension in the suture is both sufficient to close the wound properly and equalized to neutralize much astigmatism (Figures 1 and 2). The continuous suture, employing zigzag angles, distributes a portion of its force around the circular wound as apposed to radially oriented sutures, which only provide meridional support. With a zigzag continuous suture, there is a bridging suture deep in the stroma connecting any two angled surface sutures. The zigzag continuous suture acts to cradle the wound, directing the forces holding the wound together into a circular pattern, minimizing the forces acting centrally and hence increasing astigmatism. Envision this pattern in three dimensions as the suture wends its way from the corneal surface, plunging deeply into pre-Descemet’s stroma of the donor, across to the pre-Descemet’s recipient from which it resurfaces on to the recipient surface at an angle, only to be repeated again and again. With normal donor and recipient corneas, there is no advantage in placing more suture passes in any quadrant than necessary to appose the wound to a watertight degree. Depending on the recipient tissue quality and thickness, four to five passes per quadrant will be sufficient. The result will be a beautiful and functional penetrating keratoplasty.
Source: Used with permission from SLACK Incorporated
When the suture breaks, usually at 2.5 years, give or take 6 months, it is removed in its entirety at the slit lamp in a few minutes under topical anesthesia.
Comparison with the interrupted suture
The corneal wound pulled together with 16 to 18 interrupted radial sutures, often placed longishly, and each with its own tension exerted on the central cornea, creates a laundry list of problems including wound leaks, high astigmatism, frequent suture removal, wound elevation and wound dehiscence.
The zigzag suture, on the other hand, forms a single uninterrupted cord weaving back and forth in the peripheral cornea, encircling and embracing the wound. Because the sutures binding the wound together do so at relatively short distances, this single suture acts like a simple encircling band. With a zigzag continuous suture, there is a bridging suture deep in the stroma, underpinning and connecting any two angled surface sutures. The consequence of this suture configuration is a wound well apposed over all 360°, imparting a more even distribution of wound pressure and a near equal tension transmitted to the center of the transplant. It is not unusual for there to be little or no suture adjustment necessary to achieve an astigmatism-free result right on the operating table. Extreme thinness of the recipient cornea is no barrier to the surgeon using the zigzag continuous suture.
Surgeons eager to adopt this method of suturing are cautioned to read the full chapter in the upcoming book Keratoconus: A Comprehensive Practical Review to acquaint themselves with the extensive information and guidance available.
Editor’s note: The two images and portions of the text are used with permission from SLACK Incorporated.
- For more information:
- Roswell R. Pfister, MD, can be reached at Pfister Vision Correction Center, 2198 Columbiana Road, Vestavia Hills, AL 35216; email: rpfister@pfistervision.com.
- Edited by Amar Agarwal, MS, FRCS, FRCOphth, director of Dr. Agarwal’s Eye Hospital and Eye Research Centre. Agarwal is the author of several books published by SLACK Books, sister company of Healio publisher Ocular Surgery News, including Phaco Nightmares: Conquering Cataract Catastrophes, Bimanual Phaco: Mastering the Phakonit/MICS Technique, Dry Eye: A Practical Guide to Ocular Surface Disorders and Stem Cell Surgery and Presbyopia: A Surgical Textbook. He can be reached at 19 Cathedral Road, Chennai 600 086, India; email: aehl19c@gmail.com; website: www.dragarwal.com.
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