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Ophthalmology Emphasizing Corneal and Refractive Issues

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The Torque Antitorque PK Suture

The torque antitorque suture pattern (figure A), originally developed by Dr Richard Troutman, has many advantages over other suture techniques in corneal transplantation. First, the net of sutures overlying the graft edge provides protection against the outward intraocular pressure assuring against graft edge lift. Second, the arrangement of  the pattern provides direct compression across the wound, causing the cornea inside the suture bites to lift upwards and causing the central cornea to flatten  for about a month. During this time, the thin 10-0 nylon sutures “cheeswire” into the cornea, causing the flat central cornea to steepen and provide a stable environment for wound healing. Sutures are left in place for one year, based on an average time of corneal wound healing. If excessive astigmatism is a problem, additional sutures are added rather than the common practice of removing sutures early to provide (temporary) astigmatic correction.

The standard PK begins with a trephination centered on the pupil 8mm in diameter, eccentric grafts will cause astigmatism. The donor cornea is prepared with a 8.5mm trephine and placed into position with a single interrupted suture placed at 12 o”clock.. The second interrupted suture is placed 180 degrees away at 6 o’clock taking care to place the suture in such a manner that spacing on both sides of the host opening are equally spaced. Using a single suture, 4 additional bites are taken equidistantly to complete the six interrupted “stay” sutures holding the graft in place of the application of the running sutures (figure B). These are then tied off using the slip knot. All sutures should be tied tightly and at this point the cornea should be watertight. The anterior chamber can be reformed at this point.

The first running suture can then be placed, with 12 or 18 bites as the surgeon pleases, in a clockwise direction. I have found that 18 bites results in a stronger wound closure and less postoperative astigmatism. All bites are made in a radial fashion, perpendicular to the graft wound. The running suture is tied with a slip knot and tightened “hand over hand”, finished with 2 overhand throws and the knot is buried. At this point a curious observation can be made (figure C). The running suture has twisted the donor graft clockwise so that even the originally radial sutures are no longer radial. If the PK was stopped at this point, the forced across the graft wound would be twisting rather than radial and graft edge lift and/or large amounts of astigmatism would likely result.

The answer is to add a second  suture in a counter-clockwise direction, making each bite parallel to the rotated bites of the previous pass. When this running suture is tied with a slip knot and tightened, the graft will rotate counterclockwise restoring all suture bites to a radial configuration, perpendicular to the graft margin (figure D). Thus the forces across the wound will compress the tissue allowing optimal wound healing. Additionally, the original interrupted sutures will be loose and are easily removed.

Imagine that the second running suture were placed in the same clockwise direction as the first running suture. The donor graft would be further rotated and the wound healing would be further compromised.

 

 

Click on the figures above to see larger clinical views of the incision creation.

 

Corneal Astigmatism: Etiology, Prevention, and Management, CV Mosby, published 1992, Richard Troutman, M.D., Kurt Buzard, M.D.

 

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