**6. Strabismus surgical techniques: Do's and don'ts to avoid complications**

#### **6.1. Surgery to the horizontal rectus muscles**

Muscle surgery to the horizontal rectus muscles, in the form of recessing and resecting, is commonly performed for esotropia and exotropia. These muscles can also be moved away from their original line of action to treat vertical deviations, pattern strabismus (A and V), and nerve palsies. Surgery to the vertical rectus muscles is fundamentally similar to horizontal rectus muscles surgery but is less commonly performed. Each patient requires an individual surgical approach to the management of their strabismus, but the tables provided in Appendix I may be of assistance as a guide in deciding on measurements.

#### *6.1.1. General considerations*

Before surgery, make sure that the patient's head position is optimal avoiding flex of the neck. Have the patients neck extended so that the patient is looking at the surgeon sitting at the head of the surgical table. A towel roll placed under the patient's shoulders may be helpful to get the chin up (Figure 24).

**Figure 24.** Correct head position.

#### *6.1.2. Limbal vs. fornix approach*

Surgical plan for most traumatic bilateral SOP with extorsion, esotropia ≥ 10 PD in down gaze but no significant hypertropia in the primary position, is the bilateral Harada–Ito procedure

**6. Strabismus surgical techniques: Do's and don'ts to avoid complications**

Muscle surgery to the horizontal rectus muscles, in the form of recessing and resecting, is commonly performed for esotropia and exotropia. These muscles can also be moved away from their original line of action to treat vertical deviations, pattern strabismus (A and V), and nerve palsies. Surgery to the vertical rectus muscles is fundamentally similar to horizontal rectus muscles surgery but is less commonly performed. Each patient requires an individual surgical approach to the management of their strabismus, but the tables provided in Appendix

Before surgery, make sure that the patient's head position is optimal avoiding flex of the neck. Have the patients neck extended so that the patient is looking at the surgeon sitting at the head of the surgical table. A towel roll placed under the patient's shoulders may be helpful to get

and bilateral MR recessions (small) with infraplacement one-half tendon width.

**6.1. Surgery to the horizontal rectus muscles**

*6.1.1. General considerations*

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the chin up (Figure 24).

**Figure 24.** Correct head position.

I may be of assistance as a guide in deciding on measurements.

It is important to choose a proper conjunctival incision, as this can have an impact on your strabismus surgery as emphasized as one of the 10 commandments for strabismus surgery by Dr. Wright [12]. The limbal incision is made at the limbus (Figure 25) and is suitable for older patients over 40 years, as the conjunctiva is friable. For patients under 40 years, both limbal and fornix incisions are usable for rectus surgery. The fornix incision is 8 mm posterior to the limbus in the inferior fornix (Figure 26) and should therefore always be preferred for inferior and superior oblique surgery. Fornix incision is preferred to a Swan incision, which is over the muscle insertion, as Swan can leave a conjunctival scar making future surgery difficult, and careful closure is therefore required.

**Figure 25.** The limbal incision.

**Figure 26.** The fornix incision.

#### *6.1.3. Avoid fat adherence syndrome*

Posterior Tenon's capsule separates orbital fat from the extraocular muscles and sclera (Figure 27). If during periocular surgery one ruptures posterior Tenon's capsule, fat will prolapse and scar attaches to the extraocular muscle and/or the sclera (Figure 28). The scar is an adhesion that contracts causing restriction of ocular rotations (restrictive strabismus), called fat adher‐ ence, first described by Marshall M. Parks MD.

**Figure 27.** Anatomy of the posterior Tenon's capsule.

**Figure 28.** Anatomy of the posterior Tenon's capsule.

#### *6.1.4. Scleral thickness, avoid perforation*

*6.1.3. Avoid fat adherence syndrome*

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ence, first described by Marshall M. Parks MD.

**Figure 27.** Anatomy of the posterior Tenon's capsule.

**Figure 28.** Anatomy of the posterior Tenon's capsule.

Posterior Tenon's capsule separates orbital fat from the extraocular muscles and sclera (Figure 27). If during periocular surgery one ruptures posterior Tenon's capsule, fat will prolapse and scar attaches to the extraocular muscle and/or the sclera (Figure 28). The scar is an adhesion that contracts causing restriction of ocular rotations (restrictive strabismus), called fat adher‐ The scleral thickness behind the rectus muscle insertion is extremely thin, measuring only 0.3 mm. Because of the thin sclera, perforation into the globe is a significant risk during the scleral needle pass when suturing the muscle to sclera. Therefore, proper needle selection is important to reduce the risk of perforation. The preferred *side cutting or spatulated needle* has a flat top and bottom (Figure 29). The flat bottom reduces the chance of inadvertent perforation deep into the globe and the flat top prevents cutting into the roof of the scleral tunnel above. Furthermore, to avoid inadvertent perforation of the globe, it is critical that the scleral needle pass is shallow and controlled keeping the tip up and passing the needle horizontally during the scleral needle pass in a flat and straight manner.

**Figure 29.** Side cutting or spatulated needle is preferred.

#### *6.1.5. Avoid partially slipped muscle*

To hook a rectus muscle successfully, keep a small hook perpendicularly and firmly to the sclera. Then pass the hook under the rectus insertion, keeping the perpendicular orientation until the hook is under the muscle (Figure 30). This will prevent splitting of the rectus muscle as the tip of the hook stays on the sclera. After hooking the muscle, replace the small hook with the large hook as a Jameson or Helveston hook.

The pole test should then be performed to ensure the entire rectus muscle is hooked. A small hook is placed at the tip of the larger hook holding the muscle. The small hook is then pulled supero anteriorly with the tip perpendicular to the sclera (Figure 30). If the muscle is split (Figure 31), the residual fibers will restrict the small hook from moving anteriorly.

After hooking the entire rectus muscle, avoiding rupture of the posterior Tenon's capsule as previously described, it is important to secure the muscle by full-thickness locking bites, centrally and then at each edge of the muscle for three point fixation (Figure 32). Fullthickness pass at the edges is very important, as a partial thickness pass will result in a partially slipped muscle occurring at the edge that was not secured with full-thickness bite (Figure 33).

**Figure 30.** When hooking the muscle, remember perpendicular orientation of the hook.

**Figure 31.** The pole test, disclose a split muscle.

**Figure 32.** Secure the muscle by full-thickness locking bites.

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**Figure 33.** Partial thickness pass will result in a partially slipped muscle.

#### *6.1.6. Weakening and tightening procedures*

Rectus muscle recession is a weakening procedure, where the rectus muscle is detached from the globe and replaced further from the limbus. The muscle is detached from its insertion and recessed some specific mm and sutured to sclera. This shortens the distance between the origin and the insertion of the muscle and therefore has a weakening effect (Figure 34).

**Figure 34.** Recession.

**Figure 32.** Secure the muscle by full-thickness locking bites.

**Figure 31.** The pole test, disclose a split muscle.

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**Figure 30.** When hooking the muscle, remember perpendicular orientation of the hook.

If a rectus muscle is not widely splayed, there will be redundant muscle and central sag causing a larger recession than intended. Prevent central sag by adequately separating the muscle poles and by securing the center of the muscle with a central security knot. Central sag can be corrected with the same suture that holds the muscle (Figure 35)

**Figure 35.** The center of the muscle is secured with a central security knot.

Rectus muscle resection tightens the muscle by removing a segment of the muscle then advancing the muscle to the original insertion (Figure 36). Tightening effect increases when the eye rotates away from the resected muscle because the muscle gets tighter.

Rectus muscle plication has the same effect as resection as it tightens the muscle. Sutures are attached to the muscle posterior to the insertion then passes thorough sclera anterior to the insertion (Figure 37, top). The sutures are pulled up to fold the muscle (Figure 37, bottom). Plication tightens the muscle without the need for muscle disinsertion; thus, it is safer than resection. Plication spares the anterior ciliary vessels, thus reducing the risk of anterior segment ischemia. The rectus plication was invented by professor and coauthor Dr. Kenneth Wright during his fellowship and published in 1991 (Figure 37).

**Figure 36.** Resection.

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**Figure 37.** Plication.

and by securing the center of the muscle with a central security knot. Central sag can be

Rectus muscle resection tightens the muscle by removing a segment of the muscle then advancing the muscle to the original insertion (Figure 36). Tightening effect increases when

Rectus muscle plication has the same effect as resection as it tightens the muscle. Sutures are attached to the muscle posterior to the insertion then passes thorough sclera anterior to the insertion (Figure 37, top). The sutures are pulled up to fold the muscle (Figure 37, bottom). Plication tightens the muscle without the need for muscle disinsertion; thus, it is safer than resection. Plication spares the anterior ciliary vessels, thus reducing the risk of anterior segment ischemia. The rectus plication was invented by professor and coauthor Dr. Kenneth Wright

the eye rotates away from the resected muscle because the muscle gets tighter.

corrected with the same suture that holds the muscle (Figure 35)

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**Figure 35.** The center of the muscle is secured with a central security knot.

during his fellowship and published in 1991 (Figure 37).

**Figure 36.** Resection.

To perform rectus muscle recessions, resections, and plications, replace the standard hook (Jameson or Helveston hook) with the titanium *Wright grooved hook* (Figure 38). This hook allows for suturing the muscle insertion over the groove (Figure 39), thus preventing inad‐ vertent scleral perforation and making it easy to get full-thickness locking bites and keep suture placement precise and consistent: not too posterior—not too anterior. Especially when suturing tight muscles, the Wright hook helps pulling the muscle to the surgical field and provides space to suture the muscle (Figure 40). Dr. Wright holds a U.S. patent on the hook design.

**Figure 38.** Wright groove hook.

**Figure 39.** Suturing rectus muscle insertion over groove hook.

**Figure 40.** Suturing rectus muscle insertion over groove hook.

#### *6.1.7. Avoid anterior segment ischemia*

The two long posterior ciliary arteries and the anterior ciliary arteries supply circulation to the anterior segment. Each group contributes about 50% of the anterior segment blood flow. The anterior ciliary arteries course with the rectus muscles (Figure 41). The MR, SR, and IR muscles having 2 arteries and are major suppliers, while the RL has one artery and contributes little to anterior segment circulation. Removing a rectus muscle will permanently disrupt the blood flow from the corresponding anterior ciliary arteries, and the arteries do not recanalize. In children, the long posterior ciliary arteries can maintain enough flow, so even if all the rectus muscles were removed, the child will not get anterior segment ischemia. In senior adults, however, the posterior ciliary supply can be compromised from small vessel disease, and removing the 3 major supplier rectus muscles (i.e., MR, SR, and IR) can result in anterior segment ischemia. Anterior segment ischemia can cause uveitis, hypotonia, and corneal edema. Anterior ischemia is usually transient, lasting a few weeks to a couple of months; however, severe cases can result in vision loss. Treatment is low dose topical corticosteroid drops. Anterior segment ischemia has been reported to occur 10 to 20 years after strabismus surgery. The iris angiogram (Figure 42) shows hypoperfusion of the superior iris, indicating the superior rectus muscle has been removed and its ciliary vessels gone. Once a rectus muscle is removed, its ciliary vessels are permanently destroyed. Over 3 months, the collateral circulation improves especially in young persons, and the iris angiogram can revert to normal. There is no formula for the number of rectus muscles that can be safely detached. As a general rule, do not detach more than two rectus muscles at one time, unless absolutely necessary. As the two vertical and the medial rectus muscles provide the major anterior ciliary blood supply to the anterior segment, try to preserve at least one of these muscles.

**Figure 41.** The anterior ciliary arteries course with the rectus muscles.

**Figure 39.** Suturing rectus muscle insertion over groove hook.

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**Figure 40.** Suturing rectus muscle insertion over groove hook.

The two long posterior ciliary arteries and the anterior ciliary arteries supply circulation to the anterior segment. Each group contributes about 50% of the anterior segment blood flow. The anterior ciliary arteries course with the rectus muscles (Figure 41). The MR, SR, and IR muscles having 2 arteries and are major suppliers, while the RL has one artery and contributes little to anterior segment circulation. Removing a rectus muscle will permanently disrupt the blood flow from the corresponding anterior ciliary arteries, and the arteries do not recanalize. In children, the long posterior ciliary arteries can maintain enough flow, so even if all the rectus muscles were removed, the child will not get anterior segment ischemia. In senior adults,

*6.1.7. Avoid anterior segment ischemia*

**Figure 42.** The iris angiogram shows hypoperfusion localized to the superior iris due to resection of the superior rectus muscle.

#### **6.2. Surgery for oblique muscle dysfunction**

#### *6.2.1. Inferior oblique weakening*

Inferior oblique overaction, both primary and secondary, can be treated by weakening the IO muscle. The three most frequently performed procedures to weaken the inferior oblique muscle is illustrated in Figure 43 and include inferior oblique (A) myectomy—remove a segment of muscle, (B) recession—move insertion toward the origin to slacken the muscle, and (C) anteriorization—move insertion anterior to equator to change the vector of forces so the IO is no longer an elevator; it is more or less vertically neutral. If the IO is placed anterior to the inferior rectus, then the IO will pull the front of the eye down and cause limited elevation, e.g., "antielevation." It is a complication of placing the inferior oblique too anterior but can be used to treat DVD. Avoid IO myotomy, as it is not effective, because the cut ends of the muscle inevitably reunite or scar to sclera, causing residual IOOA.

**Figure 43.** The three most frequently performed procedures to weaken the inferior oblique muscle: (A) myectomy, (B) recession, and (C) anteriorization.

The ciliary nerve courses with the IO nerve, so trauma during IO surgery to the nerve can rarely cause the complication of pupil dilatation and reduced accommodation. Avoid this by using direct visualization of the posterior border of the IO muscle during hooking off the muscle. Avoid "deep blind" posterior passes to hook the muscle and use the Wright grooved hook for suturing the inferior oblique muscle insertion while protecting the sclera in the area of the macular (Figure 44).

**6.2. Surgery for oblique muscle dysfunction**

inevitably reunite or scar to sclera, causing residual IOOA.

Inferior oblique overaction, both primary and secondary, can be treated by weakening the IO muscle. The three most frequently performed procedures to weaken the inferior oblique muscle is illustrated in Figure 43 and include inferior oblique (A) myectomy—remove a segment of muscle, (B) recession—move insertion toward the origin to slacken the muscle, and (C) anteriorization—move insertion anterior to equator to change the vector of forces so the IO is no longer an elevator; it is more or less vertically neutral. If the IO is placed anterior to the inferior rectus, then the IO will pull the front of the eye down and cause limited elevation, e.g., "antielevation." It is a complication of placing the inferior oblique too anterior but can be used to treat DVD. Avoid IO myotomy, as it is not effective, because the cut ends of the muscle

**Figure 43.** The three most frequently performed procedures to weaken the inferior oblique muscle: (A) myectomy, (B)

*6.2.1. Inferior oblique weakening*

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recession, and (C) anteriorization.

**Figure 44.** The Wright grooved hook used in IO recession protects the sclera in the area of the macular.

A neurovascular bundle attaches to the posterior aspect of the IO muscle. If the posterior fibers of the IO muscle are anteriorized to the level of the inferior rectus insertion, this will stretch the neurovascular bundle and cause a "J" deformity of the IO muscle (Figure 45). The tight neurovascular bindle attached to the IO muscle will pull the eye down and limit elevation (antielevation). A better surgical technique is to keep the posterior muscle fibers posterior to avoid antielevation, unless some limitation of elevation is desired such as the case of treating DVD.

**Figure 45.** The posterior fibers of the IO muscle are anteriorized to the level of the inferior rectus insertion, stretching the neurovascular bundle and causing a "J" deformity of the IO muscle.

#### *6.2.2. Superior oblique tightening*

Two procedures that tighten the SO tendon include the full tendon tuck and the Harada–Ito procedure, which is a tightening of the anterior tendon fibers by a partial tuck or advancement of the anterior tendon fibers.

#### *6.2.2.1. Superior oblique tuck*

Extorsion associated with acquired SO palsy can be treated by tightening the anterior SO tendon fibers. The anterior SO tendon fibers are responsible for intorsion, while the posterior fibers cause depression and abduction. The SO full tendon tuck (Figure 46) tightens the tendon by pinching and folding the entire tendon. This results in intorsion, depression, and abduction. It can be used in cases of lax SO tendon causing an SOP and is therefore useful for correcting extorsion, hyperdeviation, and convergence in down gaze. If the full tendon tuck is made too tight, it will cause limited elevation worse in adduction due to tightening of the posterior tendon fibers, termed iatrogenic Brown's syndrome. Care must be taken to balance the superior oblique tightening against an induced Brown's syndrome by performing intraoperative forced ductions of the superior oblique tendon after tucking.

**Figure 46.** The SO full tendon tuck.

#### *6.2.2.2. Harada–Ito procedure*

There are clinical situations that require selective correction of extorsion without a significant change in vertical or horizontal alignment. A full tendon tuck in this situation is not appropriate as it would induce a hypotropia and iatrogenic Brown's syndrome. The Harada–Ito procedure is designed to selectively correct extorsion, as it tightens the anterior tendon thus intorting the eye. Specifically, the procedure corrects extorsion, usually caused by an SOP, as only the anterior tendon fibers of the SO are tightened so there is little depressor or abduction effect. Iatrogenic Brown's syndrome is uncommon. Harada–Ito is the procedure of choice to correct extorsion without significant vertical strabismus. Figure 47 shows the Harada–Ito as the anterior fibers in red are pulled temporally toward the lateral rectus muscle to intort the eye as shown by the red arrow.

**Figure 47.** Harada–Ito procedure includes anterior fibers of SO pulled temporally toward the LR.

There are two ways to perform the Harada–Ito as illustrated in Figure 48: (A) remove the anterior 1/3 of the fiber and advance temporally toward the lateral rectus; (B) the classic Harada–Ito procedure—leave the tendon insertion intact but split the anterior fibers and pull them temporally toward the lateral rectus muscle (plication).

**Figure 48.** Two ways to perform the Harada–Ito procedure.

*6.2.2. Superior oblique tightening*

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of the anterior tendon fibers.

*6.2.2.1. Superior oblique tuck*

**Figure 46.** The SO full tendon tuck.

*6.2.2.2. Harada–Ito procedure*

ductions of the superior oblique tendon after tucking.

Two procedures that tighten the SO tendon include the full tendon tuck and the Harada–Ito procedure, which is a tightening of the anterior tendon fibers by a partial tuck or advancement

Extorsion associated with acquired SO palsy can be treated by tightening the anterior SO tendon fibers. The anterior SO tendon fibers are responsible for intorsion, while the posterior fibers cause depression and abduction. The SO full tendon tuck (Figure 46) tightens the tendon by pinching and folding the entire tendon. This results in intorsion, depression, and abduction. It can be used in cases of lax SO tendon causing an SOP and is therefore useful for correcting extorsion, hyperdeviation, and convergence in down gaze. If the full tendon tuck is made too tight, it will cause limited elevation worse in adduction due to tightening of the posterior tendon fibers, termed iatrogenic Brown's syndrome. Care must be taken to balance the superior oblique tightening against an induced Brown's syndrome by performing intraoperative forced

There are clinical situations that require selective correction of extorsion without a significant change in vertical or horizontal alignment. A full tendon tuck in this situation is not appropriate as it would induce a hypotropia and iatrogenic Brown's syndrome. The Harada–Ito procedure is designed to selectively correct extorsion, as it tightens the anterior tendon thus intorting the The anterior SO tendon fibers are looped with a suture and displaced laterally without disinsertion (Figure 49, left drawing). The anterior fibers are sutured to sclera 8 mm posterior to the superior border of the lateral rectus muscle (Figure 33, right photo). This procedure has the advantage of being easy reversible. To undo the classic Harada–Ito, simply cut the suture and the tendon will be back to normal. This must be done within 24 to 48 h after surgery, or the tendon will scar in place.

**Figure 49.** The classic Harada–Ito (plication) method where the anterior fibers are looped with a suture and sutured to sclera laterally.

#### *6.2.2.3. Anesthesia*

General anesthesia is used most frequently in strabismus surgery. All strabismus surgery on children requires general anesthesia. Patient anxiety, reoperations, and SO surgery are also indications for general anesthesia. An experienced anesthesiologist, familiar with pediatric anesthesia and potential life-threatening complications like malignant hyperthermia, is an essential member of the surgical team.

Local anesthesia can be used in cooperative adults for unilateral surgery. A retrobulbar injection of 4 ml of lidocaine is given. If the patient experiences intraoperative pain, it can be treated with an additional local injection of lidocaine near the muscle being careful not to inject directly into the muscle. Topical anesthesia and sub-Tenon anesthesia is a good option for adult patients requiring a unilateral or bilateral recession or even resection procedures. With gentle manipulation, avoiding pulling on the muscle, topical anesthesia strabismus surgery can be done with minimal pain, without bearing the risk of general anesthesia.

#### *6.2.2.4. Sutures*

A 5-0 vicryl suture with S-24 double-arm spatula needles, or a 6-0 vicryl suture with S-29 spatula needles, are the usual sutures of choice for strabismus surgery. A 5-0 mersilene suture (nonabsorbable) is indicated for muscles that may develop a postoperative stretched scar, advancement of a slipped muscle, the Harada*–*Ito procedure, and Wright's silicone tendon expander procedure.

#### *6.2.2.5. Magnification and light source*

Magnification of 2 times is helpful or use the lowest magnification of a surgery microscope. High magnification should be avoided as it significantly limits depth of focus and field size. A head lamp is advised if a surgery microscope is not used.

#### *6.2.2.6. Postoperative care*

Immediate recovery: NPO is necessary for 2 h after surgery, depending on the age of the patient. Restricting all oral intake helps reduce nausea and vomiting postoperatively. Do not use eye patches unless an adjustable suture was used or it was a multiple reoperation.

#### *6.2.2.7. Outpatient follow-up*

Prescribe antibiotic-steroid ointment, b.i.d. × 10 days. No swimming for 2 weeks, and schedule a follow-up postoperative visit in the first week, then a second postoperative visit usually in 6 weeks, depending on the patient's condition and age. Young patients with intended overcorrection of intermittent exotropia need to be followed more frequent. Patients should be warned of the possibility of periocular infection and to return immediately if redness or swelling persists.

If you want to dig even deeper into strabismus surgery, we suggest you to read the books and papers mentioned below.

### **7. Conclusion**

**Figure 49.** The classic Harada–Ito (plication) method where the anterior fibers are looped with a suture and sutured to

General anesthesia is used most frequently in strabismus surgery. All strabismus surgery on children requires general anesthesia. Patient anxiety, reoperations, and SO surgery are also indications for general anesthesia. An experienced anesthesiologist, familiar with pediatric anesthesia and potential life-threatening complications like malignant hyperthermia, is an

Local anesthesia can be used in cooperative adults for unilateral surgery. A retrobulbar injection of 4 ml of lidocaine is given. If the patient experiences intraoperative pain, it can be treated with an additional local injection of lidocaine near the muscle being careful not to inject directly into the muscle. Topical anesthesia and sub-Tenon anesthesia is a good option for adult patients requiring a unilateral or bilateral recession or even resection procedures. With gentle manipulation, avoiding pulling on the muscle, topical anesthesia strabismus surgery

A 5-0 vicryl suture with S-24 double-arm spatula needles, or a 6-0 vicryl suture with S-29 spatula needles, are the usual sutures of choice for strabismus surgery. A 5-0 mersilene suture (nonabsorbable) is indicated for muscles that may develop a postoperative stretched scar, advancement of a slipped muscle, the Harada*–*Ito procedure, and Wright's silicone tendon

Magnification of 2 times is helpful or use the lowest magnification of a surgery microscope. High magnification should be avoided as it significantly limits depth of focus and field size.

can be done with minimal pain, without bearing the risk of general anesthesia.

sclera laterally.

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*6.2.2.3. Anesthesia*

*6.2.2.4. Sutures*

expander procedure.

*6.2.2.5. Magnification and light source*

A head lamp is advised if a surgery microscope is not used.

essential member of the surgical team.

The most important rule for the strabismus surgeon is to continue learning from experience. Surgery should be done carefully and should preoperatively be planned and thought out logically. Unexpected results should be questioned. Procedures that do not measure up to the surgeon's expectations should be altered. The surgeon should work on improving his or hers skills and develop his or hers own set of guidelines. However, it is apparent that not all surgeons will have the opportunity to operate on a sufficient number of patients to be inno‐ vative. In that case, the surgeon should select his or her authority carefully and remain ap‐ propriately skeptical and positively critical. It is not about "how many" but rather "how" you perform. Our patients deserve no less than this.
