Ординатура / Офтальмология / Английские материалы / Strabismus Surgery and Its Complications_Coats, Olitsky_2007

7.4.3 Scobee Muscle Hook

A Scobee muscle hook is a superb instrument for hooking inferior oblique muscle. Use of this muscle hook reduces tendency to grasp excess adjacent orbital structures, orbital fat, and reduces the tendency for the assistant

to lose control of the inferior oblique muscle after it has isolated on the hook. Manipulation of the inferior muscle is also easer than manipulation with other hooks (>Fig. 7.10).

7.5 Surgical Needles

Ideal surgical needle characteristics are listed in Table 7.1. Surgical needles have three basic components including a swage, a body, and a point. The swage is the site of attachment of the suture to the needle. For smaller caliber needles, a hole is drilled in the end of the needle with a laser [6]. The needle is attached to the suture by compressing the walls of the swage against the suture. This results in a smooth swage with low tissue drag force, reducing tissue trauma. Needles are more susceptible to damage in the area of the swage than in other areas.

The body of a needle is its longest component. Surgical needles should only be grasped by needle holders on the body of the needle. The body of the needle is critical for interaction with the needle holder and its ability to transmit the penetrating force of the needle to the point. Needle factors that affect performance include needle diameter and radius, body geometry, and the stainless steel alloy from which it is constructed. The important design features of a needle are shown in Fig. 7.11. The cross-sectional area of a surgical needle may be circular, rectangular, triangular, or trapezoidal. The diameter of a needle is the gauge or thickness of the needle wire. Needles used for strabismus surgery have a single radius of curvature. The radius of a needle is the distance from the body of the needle to the center of the circle along which the needle curves. The curvature of a needle with a single radius of curvature may vary

Made from high-quality stainless steel

Smallest possible diameter

Stable in needle holder

Produces minimal tissue trauma

Minimal tissue penetration resistance

Sterile

chord length of a needle is the linear distance from the point of the needle to the swage, and determines the bite width. The length of the needle is the distance measured along the needle from the tip of the point to the swage. The needle length, not chord length, is indicated on suture packaging.

The point of a surgical needle varies depending on the surgical application and the tissue to be penetrated. The point of the needle extends from the tip of the needle to the needle body. Most needles used in strabismus surgery have spatula points. These needles, originally designed for ophthalmologic surgery, are flat on the top and bottom surfaces to reduce tissue injury. The cutting edges are on the tip and sides of the point. Spatula needles allow the needles to stay in the tissue plane. They facilitate easy tissue penetration and needle control as they pass between and through tissue layers. The point of the needle may be located on the top or bottom of the needle (>Table 7.2).

7.5.1 Choosing a Surgical Needle

Several needles are manufactured for use during ophthalmologic surgery. Each strabismus surgeon should choose his/her needle(s) based upon needle design, performance, and personal preference. From a practical standpoint, larger needles are easier to handle and are easier to see as they pass through the sclera. Their disadvantages include the fact that they are

more likely to produce muscle damage when passed through the muscle and there is a tendency to pass larger needles more deeply into the sclera [7], which could increase the risk of sclera perforation (Chap. 21). Smaller caliber needles, in contrast, are more difficult to handle, but are less likely to result in damage to the muscle and they tend to be passed less deeply into the sclera. Goldstein and coworkers [8] evaluated tunnel characteristics of scleral passes based on a histological analysis of 40 needle passes in the sclera of a rabbit model. They reported that a needle with an acute curve produced a shorter pass though similar depth compared with a shallow curve needle. A needle with a cutting surface on its inferior aspect tended to produce a pass that was deeper than a needle with a cutting surface on its superior aspect. All four of the needles highlighted in Table 7.2 are acceptable for strabismus surgery and their use is a matter of surgeon preference. Other needle styles, not reviewed here, may also be useful.

Needles used to close the conjunctiva and/or Tenon’s capsule need not meet such precise specifications. These needles are passed through less vital tissue where there is little or no risk of perforations and other serious complications. Nevertheless, needles of small diameter should be used to avoid large holes in the conjunctiva.

7.5.2 Use of a Surgical Needle

The force required to pass the needle through the ocular tissue should be applied in a direction following the curvature of the needle. If the position of the needle in the ocular tissues requires adjustment, the needle should be removed and reinserted. The surgeon should never attempt to twist or bend the needle while it is engaged in tissue.

7.6 Sutures

The perfect suture would have several characteristics as outlined in Table 7.3. Unfortunately, no single suture can meet all of these criteria, thus compromises must be made depending upon the surgical situation. The choice of sutures is based on science as well as individual preferences of the surgeon. Sutures can be constructed from a single filament or multiple filaments, and are known as a monofilament and multifilament sutures, respectively (>Fig. 7.12). Sutures can be classified as absorbable and nonabsorbable. Sutures that undergo degradation in tissues with loss of tensile strength within 60 days are generally considered absorbable while those that maintain tensile strength for longer than 60 days are generally considered nonabsorbable [9]. The first stage of absorption is linear, lasting for several days to weeks. The second stage overlaps the first stage and is characterized by loss of the suture mass. Loss of tensile strength and rate of absorption are separate phenomena.

7.6.1 Absorbable Sutures

7.6.1.1 Collagen Sutures

Absorbable sutures are usually made from either collagen or synthetic polymers. Collagen sutures are derived from the submucosal lining of ovine small intestine or the serosal layer of bovine small intestine. They are treated with an aldehyde

Table 7.3. Ideal suture characteristics

Easy to manipulate

Minimal or no tissue reaction

Does not support bacterial growth

High tensile strength

Sterile

Absence of allergic potential

Absence of carcinogenic potential

Absorbed after serving its purpose

Fig. 7.12. Monofilament and multifilament sutures

solution which cross-links and strengthens the suture making it more resistant to enzymatic degradation [9]. Suture treated in this way is referred to as plain gut suture [9]. If the suture is treated with chromium trioxide, it becomes chromic gut. Plain gut suture is composed of several plies that have been twisted, machine ground, and polished, producing a smooth surface that is monofilament-like in appearance [9]. The suture absorbs through a process of lysosomal and enzymatic degradation [10]. Collagenase also appears to play a role in degradation of collagen sutures [9]. Plain gut suture is rapidly absorbed, losing its tensile strength after 7–10 days. It can produce marked local tissue reaction. The primary indication for use of plain gut suture in strabismus surgery is as an option in the closure of the conjunctiva. Its rapid degradation minimizes the amount of time that the patient may experience discomfort because of contact of conjunctival-closure suture ends with the eyelids during blinking and eye movements.

7.6.1.2 Synthetic Sutures

The development of synthetic sutures was motivated by the desire to have suture that produced less local reaction compared to collagen-based sutures. Sutures made from high-molecular- weight polyglycolic acid have been used for strabismus surgery with good success [11]. Sutures with a caliber of 6.0 are most commonly used for strabismus surgery, though some surgeons prefer a 5.0 caliber suture. Two polyglycolic-acid-based sutures are Biosorb-C (Alcon®) and Dexon “S”® (Davis and GeckTM). The use of Biosorb-C and Dexon “S” as a preferred suture for adjustable strabismus surgery done 6–24 h after the completion of surgery has been advocated by some surgeons [12]. Monofilament sutures produced from polyglycolic acid are too stiff for use in surgery. Because of this, the material is extruded into fine filaments which are braided and coated with polycaprolate for surgery [9]. These sutures degrade through hydrolysis of an ester linkage, and maintain tensile strength for 2–3 weeks.

Polyglactin 910TM (Vicryl®) is a polymer that is synthesized by the random co-polymerization of two simple hydroxy acids, glycolic acid and lactic acid. Successive monomeric units of glycolic or lactic acid are linked together by ester linkages. It is available braided or as a monofilament, though the braided suture is generally used for strabismus surgery. Polyglactin 910TM has been shown to be useful for extraocular muscle surgery because it retains sufficient strength, has low antigenicity, and is easy to use, especially if it is coated [13]. Sutures with a caliber of 6.0 are most commonly used, though some surgeons prefer 5.0 caliber sutures. Approximately 50% of its tensile strength is retained at 5 days, and mass absorption of the suture is usually complete by 42 days. The suture has high knot security. Polyglactin 910TM is coated with Polyglactin 370 plus calcium stearate, which makes the surface of the suture smoother, thus reducing its coefficient of friction and reducing tissue drag. It is available undyed or violet colored. The latter is usually preferred for strabismus surgery because of enhanced visibility. The suture undergoes hydrolysis in the body to produce its original monomers, glycolic acid and lactic acid. Be-

Chapter 7

cause these two monomers are produced under normal physiologic conditions as byproducts of several metabolic pathways, they produce minimal local reaction and systemic toxicity.

7.7 Nonabsorbable Sutures

Nonabsorbable sutures maintain their tensile strength for more than 60 days. Polyester fiber suture (Mersilene®, Ethicon) is the most commonly used nonabsorbable for strabismus surgery. This suture is composed of poly(ethylene terephthalate), which is prepared from fibers of high-molecular-weight, long-chain, linear polyesters. The sutures are braided to optimize handling properties. Mersilene® exhibits a minimal acute tissue inflammatory response. Over time, the suture is encapsulated by fibrous connective tissue. No significant decline in the strength of polyester sutures occurs over time. The suture can become extruded, however, producing unwanted signs and symptoms as outlined in Chap. 19. The most common uses of polyester fiber sutures include posterior fixation sutures and muscle union procedures such the Jensen procedure (Chap. 13). Ludwig [14] has advocated the use of nonabsorbable sutures in the repair of a lengthened, stretched, remodeled scar between an operated muscle tendon and sclera which she believes is a common factor contributing to the variability of outcome after strabismus repair, resulting in overcorrection even years after surgery. She believes that definitive repair requires firm reattachment of tendon to sclera using nonabsorbable sutures (Chap. 23).

7.8 Surgical Gloves

In general, powder-free gloves are preferred for ophthalmologic surgery, including strabismus surgery. Starch powdered gloves increase the risk of sterile intraocular and extraocular inflammation [15]. Latex-free gloves should be used for patients who have latex allergy and for those who are susceptible to latex allergies, such as patients with spina bifida [16].

7.9 Magnification

The vast majority of strabismus surgeons use magnification in the form of surgical loupes to perform strabismus surgery. Some surgeons use microscope magnification and others prefer no magnification at all. While magnification is not absolutely essential for performing strabismus surgery, it can be very useful when performing critical tasks such as passing needles through the sclera and during tedious dissection. The choice and amount of magnification remain issues of surgeon preference, but in general magnification of 2× to 2.5× is sufficient. Higher degrees of magnification result in a smaller field of view and also are associated with heavier, more bulky surgical loupes. The surgeon should consider a lightweight pair of loupes, which are associated with less surgeon fatigue during

surgery. Surgical loupes with integrated optics often provide superior comfort and, in the opinion of many surgeons, superior optics compared to flip down or hand band mounted loupes (>Fig. 7.13). A headlight can be utilized depending on surgeon preference for all or for selected strabismus cases.

Fig. 7.13a,b. Surgical loupe styles for magnification during strabismus surgery. a Flip down optics, and b integrated optics

References

1.Speaker MG, Milch FA, Shah MK, Eisner W, Kreiswirth BN (1991) Role of external bacterial flora in the pathogenesis of acute postoperative endophthalmitis. Ophthalmology 98:639–649; discussion 650

2.Isenberg SJ, Apt L, Yoshimori R, Khwarg S (1985) Chemical preparation of the eye in ophthalmic surgery. IV. Comparison of povidone-iodine on the conjunctiva with a prophylactic antibiotic. Arch Ophthalmol 103:1340–1342

3.Isenberg S, Apt L, Yoshimuri R (1983) Chemical preparation of the eye in ophthalmic surgery. I. Effect of conjunctival irrigation. Arch Ophthalmol 101:761–763

4.Apt L, Isenberg S, Yoshimori R, Paez JH (1984) Chemical preparation of the eye in ophthalmic surgery. III. Effect of povidoneiodine on the conjunctiva. Arch Ophthalmol 102:728–729

5.Perry LD, Skaggs C (1977) Preoperative topical antibiotics and lash trimming in cataract surgery. Ophthalmic Surg 8:44–48

6.Ahn LC, Towler MA, McGregor W, Thacker JG, Morgan RF, Edlich RF (1992) Biomechanical performance of laser-drilled and channel taper point needles. J Emerg Med 10:601–606

7.Hussein MAW, Coats DK, Harris LD, Sanchez CR, Paysse EA. Ultrasound biomicroscopy characteristics of scleral tunnels created with needles commonly used during strabismus surgery. Binocul Vis Ocular Motil Q (in press)

8.Goldstein JH, Prepas SB, Conrad SD (1982) Effect of needle characteristics in strabismus surgery. Arch Ophthalmol 100:617–618

9.Szarmach RR, Livingston J, Rodeheaver GT, Thacker JG, Edlich RF (2002) An innovative surgical suture and needle evaluation and selection program. J Long Term Eff Med Implants 12:211–229

10.Salthouse TN, Williams JA, Willigan DA (1969) Relationship of cellular enzyme activity to catgut and collagen suture absorption. Surg Gynecol Obstet 129:691–696

11.Apt L, Henrick A (1976) “Tissue-drag” with polyglycolic acid (Dexon) and polyglactin 910 (Vicryl) sutures in strabismus surgery. J Pediatr Ophthalmol 13:360–364

12.Neumann D, Neumann R, Isenberg SJ (1999) A comparison of sutures for adjustable strabismus surgery. J AAPOS 3:91–93

13.Saunders RA, Helveston EM (1979) Coated Vicryl (polyglactin

910)suture in extraocular muscle surgery. Ophthalmic Surg 10:13–18

14.Ludwig IH (1999) Scar remodeling after strabismus surgery. Trans Am Ophthalmol Soc 97:583–651

15.Sellar PW, Sparrow RA (1998) Are ophthalmic surgeons aware that starch powdered surgical gloves are a risk factor in ocular surgery? Int Ophthalmol 22:247–251

16.Pires G, Morais-Almeida M, Gaspar A et al (2002) Risk factors for latex sensitization in children with spina bifida. Allergol Immunopathol (Madr) 30:5–13

Techniques of Exposure and Closure and Preliminary Steps of Surgery

8

In this textbook, we have chosen to emphasize the techniques of exposure of the operative site and closure of the conjunctiva for strabismus surgery in a separate chapter. These techniques are similar for all strabismus operations. Therefore, this chapter describes techniques to isolate and dissect the fascial tissues associated with each of the extraocular muscles, while the techniques required for recession, resection, tucking, and other procedures are described in other chapters, as appropriate. In addition, preliminary steps that are important to perform in many strabismus operations are reviewed in this chapter.

8.1What to do Prior to Making a Conjunctival Incision

for Strabismus Surgery

Three important steps are recommended prior to making an incision for strabismus surgery. These steps include: (1) visual inspection of the patient’s conjunctiva to help facilitate later wound closure, (2) forced traction testing of the rectus muscles and/or oblique muscles as needed, and (3) visual and/or tactile identification of the rectus muscle(s). Additionally, the spring back test may be useful if a slipped or lost muscle is suspected preoperatively.

8.1.1Visual Inspection of the Patient’s Conjunctival Anatomical Landmarks

The surgeon should carefully inspect the patient’s conjunctival anatomy prior to making an incision. Inspection may disclose previously undetected defects or lesions of the conjunctiva such as symblepharon, cysts, filtration blebs, evidence of prior surgery, and other lesions. Visual inspection prior to surgery is often the first clue that the patient has undergone previous strabismus surgery, as patients are often unaware of previous surgery, especially if surgery was done in early childhood. Inspection of the medial aspect of the conjunctiva is especially important if surgery will be carried out in this area. Closure complications of the medial conjunctiva such as advancement of the plica semilunaris may be avoided if the surgeon

Chapter

8

has inspected this area preoperatively and knows what the area should look like after closure (Chap. 19).

8.1.2Visual and Tactile Identification of the Rectus Muscles

The surgeon is obligated to identify the rectus muscle(s) to be operated and adjacent rectus muscles that may be encountered during surgery before making an incision into the conjunctiva. The rectus muscles are usually easy to identify through two simple techniques. The anterior ciliary vessels readily mark the location of the rectus muscle insertions. As the eye is rotated back and forth with forceps, these vessels can be easily seen in the episcleral space moving beneath the conjunctiva (>Fig. 8.1).

While this provides an initial estimation of the position of the rectus muscle insertion, the most effective way to determine the location of the border of a rectus muscle is to palpate it using a blunt object such the heel of a muscle hook. A muscle hook is placed against the conjunctiva approximately 8–10 mm posterior to the limbus in the space between two adjacent rectus muscles. While exerting mild pressure on the hook against the globe, the hook is moved toward the rectus muscle. When contact with the border of the rectus muscle is made, the hook can no longer be advanced and the muscle will become bunched against the hook, clearly identifying its border (>Fig. 8.2).

8.1.3 Rectus Muscle Forced Traction Testing

Traction testing should be done when indicated prior to initiation of surgery. Rectus muscle traction testing can be done in the office or in the operating room. In the operating room, traction testing is often performed on both eyes even if only one eye is undergoing surgery. While some surgeons perform traction testing on all patients prior to surgery, others limit traction testing to those with a history of previous surgery and/or the presence of abnormal ductions noted in the office prior to surgery. Traction testing is easy to perform, but can be associated with complications including conjunctival tears, hemorrhage, and corneal abrasion.

8.1.4Oblique Muscle/Tendon Forced Traction Testing

If surgery is to be performed on the oblique muscle, oblique muscle tracking testing may be indicated prior to surgery to help with surgical planning and during surgery to help assure complete inferior oblique myectomy or superior oblique tenectomy has taken place. Oblique muscle traction testing is only performed under general anesthesia. The technique is most useful prior to surgery on the superior oblique tendon, where results of the test may alter the planned surgical procedure. A patient with a fourth nerve palsy who has a very lax superior oblique tendon may warrant tucking of the tendon rather than a planned inferior oblique weakening procedure, for example. If a decision not to tuck the superior oblique tendon is made, the results of superior oblique tendon traction may help in planning future surgery, if needed.

While inferior oblique muscle traction testing is generally less useful than traction testing of other extraocular muscles, the technique has specific important indications. The test can be used to confirm that the entire inferior oblique muscle has been disinserted or transected during surgery. Failure to fully disinsert or transect the inferior oblique muscle during weakening procedures usually fails to produce the desired postoperative result. Unfortunately, the test is not without limitations in this setting and may fail to detect a residual band of intact inferior oblique muscle in some situations [1]. The technique may also be useful in helping to determine if an inferior oblique muscle that has previously undergone myectomy has become reattached to the globe, when considering reoperation on the inferior oblique muscle.

8.1.4.1Technique for Forced Traction Testing of the Superior Oblique Muscle/Tendon

Guyton [2] described a traction test to determine the tightness of both the superior oblique tendon/muscle and the inferior oblique muscle. The technique was later modified by Plager [3] and the procedure described by Plager is reviewed below. A similar technique is used for the Guyton approach. An ad-

Fig. 8.3a,b. Rectus muscle forced traction testing. a The eye is grasped with forceps 1–2 mm posterior to the corneal limbus and is rotated first horizontally and then vertically. b Manual rotation of the globe laterally is incomplete in an eye with a tight medial rectus muscle

vantage of the approach suggested by Guyton is the fact that traction testing can be performed on both the superior and inferior oblique muscles without changing the position of the forceps on the globe.

To assess the tautness of the superior oblique tendon, while seated above the patient’s head the globe is firmly grasped at the 4 o’clock and 10 o’clock positions for the right eye (2 o’clock and 8 o’clock positions for the left eye), approximately 1–2 mm posterior to the corneal limbus with fine forceps (>Fig. 8.4a). The next step is critical to oblique muscle traction testing. The surgeon then gently presses the eye into the orbit and simultaneously moves the eye up and in (>Fig. 8.4b). This places the superior oblique tendon under maximum traction. The relative laxity or tautness of the superior oblique tendon can then be palpated. Movement of the globe up and in during this maneuver is limited by a normal and by a tight superior oblique tendon (>Fig. 8.4c), compared with a lax tendon (>Fig. 8.4c).

The surgeon can gain additional information by abducting and adducting the eye while simultaneously pressing the globe into the orbit and elevating it (>Fig. 8.5a). As this maneuver is carried out, the superior oblique tendon can be palpated as the globe rolls over the tendon, which has been placed under traction. The profile of the path of deflection of the globe as it is rotated resembles that of a speed bump in a roadway

Fig. 8.4a–c. Superior oblique traction testing. a The globe is firmly grasped at the 4 o’clock and 10 o’clock positions for the right eye (2 o’clock and 8 o’clock positions for the left eye). b While gently pressing the globe into the orbit, the surgeon simultaneously elevates and

adducts the eye, putting the superior oblique tendon under stretch. c Movement of the eye up and in is not limited when the tendon is lax, but is limited by a normal tendon

Fig. 8.5a–c. Superior oblique traction testing, continued. a The globe is abducted and adducted while simultaneously pressing the eye into the orbit and elevating it. b The profile of the palpated path deflection

(>Fig. 8.5b). The amount of deflection caused by the tendon as the eye rolls over it depends on the relative tautness of the tendon. The possible contour of the palpated deflection path is shown in Fig. 8.5c. The intraoperative appearance of a normal and a lax superior oblique tendon are shown in Fig. 8.6.

8.1.4.2Technique for Forced Traction Testing of the Inferior Oblique Muscle

The procedure is similar to that described for superior oblique traction testing. The globe is firmly grasped at the 2 o’clock and 8 o’clock positions for the right eye (4 o’clock and 10 o’clock positions for the left eye), approximately 1–2 mm posterior to the corneal limbus, with fine forceps. While pressing the globe into the orbit the surgeon simultaneously depresses the globe. Next, the eye is abducted and then adducted. Unlike superior oblique traction testing, traction testing of the inferior oblique muscle is not usually quantified. The muscle is either palpated or not palpated. The path deflection palpated as the eye is rotated and rolls over the inferior oblique muscle resembles that of a speed hump in a roadway (>Fig. 8.7a). The contour of the palpated deflection path is shown in Fig. 8.7b.

of the globe created by the tendon resembles that of a speed bump in a roadway. c The deflection produced by the tendon is dependent on the relative tautness of the tendon

8.1.5Spring Back Test for Slipped or Lost Muscle

If a slipped or lost muscle is suspected preoperatively, the spring back test can be helpful prior to starting surgery to help confirm the diagnosis [4]. Upon release, fibro-elastic properties of a rectus muscle cause the globe to recoil back to the mid-

Fig. 8.6a,b. Intraoperative appearance of the superior oblique tendon. a Normal superior oblique tendon, and b a lax superior oblique tendon (b is Courtesy of David A. Plager, MD)

Fig. 8.7a, b. Inferior oblique muscle traction testing. a The path deflection palpated as the eye is abducted and adducted while simultaneously pressing the globe into the orbit and depressing it resembles that of a speed hump in a roadway. b The contour of the palpated deflection path is shown

line after the globe has been mechanically deflected away from the muscle in an anesthetized patient. This normal recoil does not occur if the muscle is severely slipped or detached from the globe.

The globe is grasped with fine forceps 1–2 mm posterior to the corneal limbus and fully displaced away from the suspected slipped or lost muscle (>Fig. 8.8a). The globe is then released while the surgeon observes for recoil of the globe back to or beyond the midline. If the rectus muscle is appropriately attached to the sclera, the eye will recoil or spring back to the primary position (>Fig. 8.8b). If there is a severely slipped or lost muscle, the globe will fail to recoil, but instead will maintain its relative position after release of the forceps (>Fig. 8.8c).

8.2Conjunctival Incisions

for Rectus Muscle Surgery

All strabismus surgery requires an incision through the conjunctiva and through Tenon’s fascia. Conjunctival incisions made during strabismus surgery are created to gain access to the episcleral space (sub-Tenon’s space) and all manipulations of the extraocular muscles during routine strabismus surgery occur in this space (Chap. 1). Three surgical techniques to gain access to the episcleral space have been popularized. The two most common conjunctival incisions used for strabismus surgery today are referred to as the limbal conjunctival incision [5] and the fornix [6] (cul-de-sac) conjunctival incision. Fornix incisions are made between adjacent rectus muscles starting approximately 8 mm from the limbus, though their position and orientation may vary significantly depending on surgeon preference and the procedure planned. Limbal incisions involve the creation of a flap incision that is initiated at

Fig. 8.8a–c. The spring back test for a slipped or lost rectus muscle. a The is globe fully displaced away from the suspected slipped or lost muscle with forceps. b The eye will recoil or spring back to the primary position if the muscle is adequately attached to the globe. c The eye fails to return toward the primary position in this eye which has had its medial rectus muscle disinserted, instead maintaining its deflected position