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168 Ferenc Kuhn

Q Fig. 2.2.2 Sutures work via tissue compression. a All sutures, even if they were introduced in a different geometrical formation (thick, continuous line), want to form a circle (dotted line) upon tightening; the tissue it "encircles" is compressed. b,c All sutures have a compression zone: this is greatest in the plane of the suture itself and gradually decreases with increasing distance from that plane. To create a watertight seal, the compression zones should overlap or at least "touch" each other. If the compression zones do not meet, gaping occurs. d The gaping can be eliminated by further tightening of the existing suture(s), but this may cause major tissue distortion. The proper way to create watertightness is either via the introduction of additional suture(s) (left) or by using sutures with longer bites (right), which have larger compression zones.1 The effect of tissue compression is reflected on the corneal surface; this is why it is advisable to check the tightness of the sutures at the conclusion of wound closure (Fig. 2.2.3). Upon suture removal, the tissue compression effect disappears2

1 Other techniques are also available if there is gaping: (cyanoacrylate) glue, bandage contact lens, patch graft, PK.

2 Conversely, misalignment (tissue shift or override) caused by improper suturing is permanent.

Fig. 2.2.3 Intraoperative keratoscopy following closure of a large corneal wound. Using the keratoscope, a Flieringa ring, or a safety pin allows detection of undesirable irregularities. Alternatively, an adjustable slip knot can also be used [9]. (Courtesy of B. Hamill, Houston, TX)

Use of running suture:

recommended

Use of running suture: not recommended

Use of running suture:

recommended

Use of running suture: not recommended

Q Fig. 2.2.4 Interrupted vs running sutures. a Interrupted sutures provide maximal flexibility (length, tension, number, adjustability) but require more work (e.g., repeated steps of introduction, tying, burying the knot, and adjustment). b Running sutures have the advantage of creating an even, continuous zone of compression and require less work,1 but they cause flattening of the underlying convex structure. Running sutures tend to cause gaping in the wound's midsection (shadedarea), and the surgeon must counter this by increasing the tension on the suture, which enhances the flattening effect. c If a running suture's individual bites are introduced at the traditional 90° angle,2 the wound lips shift to create equal distribution of the tension. Unlike tissue compression, which disappears upon suture removal, this shift is permanent (see above). d To prevent tissue shift (slippage), the bites of a running suture should be introduced at 45°. Alternatively, a bootlace suture (a second, mirroring suture line) can be used. Both running sutures are introduced at 90° in the latter case. e Running suture should be used if the wound is: in the periphery; rather long; and limbus-parallel. f In all cases other than e, interrupted sutures should be used to avoid corneal flattening

1 Unless, of course, they break as they are being tied or buried

2 Which is a must with interrupted sutures

Fig. 2.2.5 The order of suture introduction in the cornea. a If the wound is long and transects the cornea, the risk of flattening the corneal dome shape by the scar is significant [34]. To counter this effect, suture introduction should start from the two peripheries and with long bites; the bites get progressively shorter as the center is approached. In the apex of the cornea - the visual center - no suture should be placed unless absolutely necessary. The numbers indicate the order of suture placement. b If the wound crosses the limbus, the limbus is closed first since this is an absolute indicator of proper apposition; the corneal part is closed second and the scleral part last. c An angular wound's (left) initial suture must be placed at the angle (right). Suturing should proceed from, instead of toward, the angle; otherwise, too much tension needs to be placed on the final suture to achieve watertightness, which would result in major tissue distortion. d In most other cases the typical "divide at 50%" rule may be applied

Fig. 2.2.6 The depth of corneal sutures. a Traditionally, corneal sutures are recommended to be 90% deep, although this has obvious disadvantages1. b A full-thickness suture immediately and permanently closes the wound; this effectively blocks the access of aqueous to the stroma. Sutures of 100% depth shorten the time the cornea needs to become dry and clear, hastening visual recovery for the patient and reducing the time until the deeper structures of the eye can be examined. Vitreoretinal surgery can thus be performed when this is necessary, not when it is possible. c A full-thickness suture also prevents tissue misalignment ("override") caused by unequal suture depth. d The direction of the needle during the three components of the introduction of a full-thickness suture. Upon entry, the needle's tip2 is held almost perpendicular to the corneal surface (top; in the AC, the vector of needle movement is more or less parallel to the surface; upon exit (center), the needle's tip is again turned almost perpendicular to the corneal surface (bottom)

Fig. 2.2.6 The depth of corneal sutures. a Traditionally, corneal sutures are recommended to be 90% deep, although this has obvious disadvantages1. b A full-thickness suture immediately and permanently closes the wound; this effectively blocks the access of aqueous to the stroma. Sutures of 100% depth shorten the time the cornea needs to become dry and clear, hastening visual recovery for the patient and reducing the time until the deeper structures of the eye can be examined. Vitreoretinal surgery can thus be performed when this is necessary, not when it is possible. c A full-thickness suture also prevents tissue misalignment ("override") caused by unequal suture depth. d The direction of the needle during the three components of the introduction of a full-thickness suture. Upon entry, the needle's tip2 is held almost perpendicular to the corneal surface (top; in the AC, the vector of needle movement is more or less parallel to the surface; upon exit (center), the needle's tip is again turned almost perpendicular to the corneal surface (bottom)

1 1 It is difficult to determine in a real life situation where that 90% exactly is. 2 Tissue thickness differs on the two sides of the wound, due to different degrees of edema. 3 Manipulation of the wound edges with forceps to "peek" inside the wound to verify needle depth is traumatic to the cornea, increasing edema development and thus interfering with postoperative visualization. 4The 10% of the wound, which is left unsutured (arrows), allows aqueous access to the stroma, extending the duration of edema. 5 The endothelium has a larger area to cover, slowing postoperative recovery.

2 "Tip" here also represents the shaft or axis of the needle.

O Fig. 2.2.7 Details of creating an "ideal" knot. Certain steps of suture management are modeled here to show the creation of a knot that is small enough to allow easy burying while providing sufficient postoperative strength to maintain wound closure. A string represents the suture, a salad server the needle holder, and a metal bar the wound. a The first step is a triple throw over the needle holder. Notice that the left-handed surgeon's right hand, which holds the long arm of the suture (the one that has the needle on its end), is on the left side of the wound (close to himself). b The first step is being completed. The surgeon has crossed his hands: the right hand is now on the right side of the wound (away from himself). The triple throw is clearly visible and the suture is properly aligned. Notice that the suture is tightened perpendicular to the plane of the wound. c Close-up of the properly aligned triple throw. d If the surgeon does not cross his hands (notice that the left hand with the needle holder is on the right side of the wound), a large tangle is formed as the triple throw is tightened. This tangle makes it more difficult to satisfy the two requirements of the knot: strong yet small. e Close-up of the improperly aligned triple throw (compare it with the image in c). f The second step in creating a proper knot is a single throw, which is tightened parallel to the plane of the wound (i.e., perpendicular to the plane of the first, triple throw). This locks the knot: once tightened, it is impossible for the knot to become loose. g The final step is another single throw, which is tightened perpendicular to the plane of the wound (i.e., parallel to the plane of the first, triple throw). This provides extra reassurance that the know will not loosen with time

Fig. 2.2.8 Closure of the star-shaped wound. a The corneal wound from the surgeon's view. b The initial suture is an intrastromal one in the center (top: surgeon's view; bottom: cross-sectional view). The intrastromal suture is placed roughly at mid-depth. It is a permanent suture (i.e., never to be removed). c Enlarged view of b, top. d The intrastromal suture brought all wound edges together, and have created several individual wounds, which are now dealt with one at a time. This is done in a way determined by the location and length of the individual wounds (see earlier). These sutures are full thickness. Top: surgeon's view; bottom: cross-sectional view d

Fig. 2.2.8 Closure of the star-shaped wound. a The corneal wound from the surgeon's view. b The initial suture is an intrastromal one in the center (top: surgeon's view; bottom: cross-sectional view). The intrastromal suture is placed roughly at mid-depth. It is a permanent suture (i.e., never to be removed). c Enlarged view of b, top. d The intrastromal suture brought all wound edges together, and have created several individual wounds, which are now dealt with one at a time. This is done in a way determined by the location and length of the individual wounds (see earlier). These sutures are full thickness. Top: surgeon's view; bottom: cross-sectional view

Fig. 2.2.9 Closure of perpendicular vs oblique (shelved) wounds. a If the wound's plane is close to vertical as it relates to the surface1, the needle's entry and exit points should be at equal distance from the wound on both the epithelial and endothelial corneal surfaces (xi=yi) and (x2=y2). b If the wound's plane is oblique, use of full-thickness sutures becomes especially crucial. The distances as measured for needle entry and exit relative to the edge of the wound need to be modified so as to create the same compression on either side. As shown, the epithelial distance on one side is matched up with the endothelial distance on the other side fo=y2) and (xi=y2). This technique prevents tissue override, which is a permanent2 abnormality

Fig. 2.2.9 Closure of perpendicular vs oblique (shelved) wounds. a If the wound's plane is close to vertical as it relates to the surface1, the needle's entry and exit points should be at equal distance from the wound on both the epithelial and endothelial corneal surfaces (xi=yi) and (x2=y2). b If the wound's plane is oblique, use of full-thickness sutures becomes especially crucial. The distances as measured for needle entry and exit relative to the edge of the wound need to be modified so as to create the same compression on either side. As shown, the epithelial distance on one side is matched up with the endothelial distance on the other side fo=y2) and (xi=y2). This technique prevents tissue override, which is a permanent2 abnormality

1 Which is the majority of the cases

2 i.e., it does not disappear with suture removal

Fig. 2.2.10 Closure of a complex, angled corneal wound. The wound that has two angles should be considered as three separate wounds. To achieve this, the single wound is first divided into three by placing the first two sutures at the angles (as in Fig. 2.2.5c). The two peripheral wounds are closed then, and the central part last. The numbers represent the order of suture placement

Fig. 2.2.10 Closure of a complex, angled corneal wound. The wound that has two angles should be considered as three separate wounds. To achieve this, the single wound is first divided into three by placing the first two sutures at the angles (as in Fig. 2.2.5c). The two peripheral wounds are closed then, and the central part last. The numbers represent the order of suture placement f „1* 1

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