Complex Strabismus Pearls
Laura B. Enyedi, MD
GENERAL PEARLS FOR COMPLEX STRABISMUS
If you do not know which surgery to perform, select the one that is easier and/or has fewer complications.
Always think ahead. Have a plan B (and C!). Consider staging surgery if very complex.
Think about comitance and matching deficits.
Patients usually accept undercorrection better than overcorrection.
Do not “flip the hyper,” especially in downgaze (see below discussion in thyroid eye disease [TED]).
If there is a muscle restriction, do a surgery that relieves the restriction.
Recheck forced ductions intraoperatively after a restricted muscle is removed. Sometimes restrictions will remain even after the muscle is completely off the eye because of orbital tissue involvement (ie, TED). This problem is very difficult to correct.
If you cannot relieve the restriction, consider matching the deficit on the fellow eye.
Make sure you understand the patient’s goals for surgery (eg, do they want to “look normal” or are they hoping to regain stereopsis or improve vision), and during the preoperative discussion, carefully communicate what is realistically attainable (see Chapter 58).
Identify if the patient has any special needs for work or hobbies (eg, diplopia in upgaze is a problem for competitive cyclists or skydivers).
Adjustable sutures (see Chapter 48) can be a great option in unpredictable situations. BUT…:
Choose patients for adjustable sutures carefully. A “rehearsal” with q-tips preoperatively can yield valuable information.
Be prepared for bradycardia, asystole, fainting, and vomiting during adjustment procedures. If the patient has a vagal response, have the patient lean the head forward between the knees or lay the examination chair flat with the feet elevated. An alcohol wipe directly under the nose can sometimes alleviate nausea. Be wary of vagal responses in family members present during adjustment.
If you cannot make things perfect at the end of a muscle adjustment, leave the patient with the easier deviation to correct during the next surgery.
Operating on the “good eye” is sometimes necessary for the best outcome.
Consider the “Law of Diminishing Returns,” an economic theory that applies to complex reoperations: The more surgery done on a patient, the lower the expectation for a great result.
The patient did not respond to the other surgeries as expected.
The anatomy is distorted from the previous surgeries making results even less predictable.
You cannot fix everyone, and some eyes do not want to be straight!
In the words of Edward G. Buckley, MD, “Once you operate on a patient, their problem becomes your problem.”
STRABISMUS IN THYROID EYE DISEASE (TED)
TED is one of the most common and most challenging forms of incomitant restrictive strabismus.
General guidelines
Smoking is a modifiable risk factor for strabismus in TED. Encourage patients to stop or reduce smoking!
Patients often need multiple surgeries (orbital, strabismus, lid).
Orbital decompression is done first because it can affect strabismus.
Strabismus surgery is done next.
Can impact lid position.
• Especially worsened lid retraction with vertical muscle recessions.
• Warn patients about worsening of dry eye and cosmesis.
Eyelid surgery is the last step.
Avoid operating on patients in the active phase of disease.
Patients are often eager for their surgery and may pressure you to do surgery expediently.
TED is often disfiguring, and diplopia can be very disabling for patients.
Depression and anxiety are common in patients with TED.
Strabismus measurements should be stable for 4-6 months pre-op.
While awaiting stability, the goal is to help the patient function with diplopia (see Chapter 56).
Incomitance limits the use of prisms to correct diplopia.
Fresnel prisms are often used because of the size and variability of the deviation.
For some patients, the size of the deviation makes suppression or ignoring the second image easier. When the strabismus improves and the images
come closer together, the brain may have more difficulty ignoring the second image. Discuss this with patients preoperatively.
Patching or use of occlusive foils can be helpful.
Consider oral steroids for a short time (days-week) before and after strabismus surgery if the patient has had a difficult course (very severe, difficult to control, relapses) or still seems inflamed.
Using a clinical activity score can be helpful in determining if a patient has active disease. Signs of active disease vary and may include conjunctival chemosis and injection, lid swelling, lid retraction, proptosis, strabismus, exposure keratopathy, and optic neuropathy. If a patient has moderate to severe active disease consider treatment with IV pulse steroid administration (commonly used in Europe). In addition, teprotumumab (insulinlike growth factor-1 receptor inhibitory antibody) has shown promising results in clinical trials for reducing proptosis and alleviating diplopia.
Some patients with dysthyroid optic neuropathy do not show signs of active disease. Abnormal color vision, exophthalmometry >20 mm, and visual field defects (arcuate or altitudinal defects, central/paracentral scotomas, or generalized depression) are common. Most of these patients have normal-appearing optic nerves. Apical muscle crowding is usually seen in patients with dysthyroid optic neuropathy. If there is a delay in treatment, patients can develop permanent optic nerve atrophy and irreversible vision loss.
Set realistic goals for surgery with the patient.
Focus on achieving orthotropia in primary and reading position.
Expand binocular field of single vision.
Decrease anomalous head position.
Alleviate torsion.
Patient may still be able to “find” diplopia.
Incomitance is common postoperatively.
Patients may need prism postoperatively.
Consider comitance and torsion:
The most important fields for most patients are primary gaze and down gaze.
Beware of “flipping the vertical” in downgaze!
Patients do NOT tolerate reversing the hypertropia and will usually be more comfortable undercorrected than overcorrected.
The amount of prism the patient can tolerate in downgaze helps determine how much inferior rectus (IR) recession can be done without causing reversal of the hypertropia.
Consider torsion especially with involvement of vertical muscles.
Consider torsion if the patient cannot fuse with prism at the corrected angle.
The normal strabismus tables (see Chapter 42) are guidelines for surgical amounts but often do not apply well in TED.
May need big surgery for small deviations and small surgery for big deviations:
Small vertical deviations may require asymmetric bilateral surgery in larger amounts than would be expected for the size of the deviation.
Small recessions of very tight muscles may give larger than anticipated effects, especially if antagonist muscles are involved.
Results are unpredictable and reoperation rates are high (40%-60%):
Some need for postoperative prism is common.
Consider the use of adjustable sutures (see Chapter 48):
The deviation can change days to weeks after surgery.
Late overcorrections are the most common postoperative change.
Especially problematic with IR recession to “flip the hyper.”
In general, patients tolerate undercorrection of hypertropia better than any overcorrection.
Leave patients undergoing IR recession undercorrected by several prism diopters, especially if they can fuse with a slight chin up.
• If you do overcorrect these patients and reverse the hypertropia:
Consider advancing the recessed IR rather than recessing a superior rectus (SR) so that you can get the desired correction in downgaze.
Consider posterior fixation suture (“adjustable Faden”) on the contralateral eye (see Chapter 49).
Because of the tendency for late overcorrection in these cases possibly due to scar elongation and slippage, there has been debate regarding the use of adjustable verses nonadjustable suture techniques and absorbable verses nonabsorbable suture in TED. It is felt that the use of absorbable and adjustable sutures might impede anchorage of the muscle to the sclera. However, multiple studies have found better success rates with adjustable suture use.
Forced duction testing (FDT) is important to evaluate restrictions and guide the surgical approach and surgical amounts.
Patients often have dry eye and exposure; keep the cornea well lubricated during strabismus surgery. A small moistened Weck-cell sponge can be placed over the cornea to keep it from drying out during surgery.
Strabismus is often complex with multiple muscles involved in one or both eyes.
Imaging may help guide diagnosis and surgical approach (see Chapter 57).
The most common muscles involved are the IR and medial rectus (MR).
The SR and lateral rectus (LR), and rarely the oblique muscles may also be involved.
Most patients have bilateral but asymmetric involvement.
Orbital tissues are also involved and can contribute to the restrictive strabismus. Taking the muscle off the eye may not completely relieve the restriction.
Consider effects of restriction and strabismus surgery on the secondary and tertiary actions of the muscle as well as the primary action.
IR involvement may worsen esotropia.
Be cautious with MR recession at same time as IR recession—because of A-pattern exotropia (XT) postoperatively (see below).
Be particularly cognizant of torsional effects and pattern strabismus.
Extorsion is common and often relieved with IR recession.
Intorsion is less common and can be difficult to treat.
Superior oblique (SO) involvement (uncommon) may cause more intorsion (or less extorsion) than one would expect with tight IR’s.
SO tenotomies may not have as much torsional effects in TED as one would normally expect because of orbital tissue involvement.
DelMonte described inferior oblique (IO) advance and superior transposition (see Chapter 46) as an effective technique for intorsion in TED (Fig. 59.1,
Video 59.1).
Transpose the IO under the LR and suture the IO at the superior edge of the LR and 8-mm posterior to LR insertion.
Corrects about 10 degrees intorsion per eye.
Can do bilaterally for more torsion effect.
Collapses A-pattern.
For vertical deviations with small amounts of torsion, consider combining IR recession w/contralateral SR recession (also see below).
Balances torsional effects.
Reduces the amount of IR recession needed (and potentially avoids overcorrecting the hyper in downgaze).
FIGURE 59.1. Inferior oblique advancement under the lateral rectus to treat intorsion in TED.
Bilateral IR recession can create A-pattern XT in downgaze.
To avoid this problem, consider unilateral IR recession if possible.
For bilateral IR involvement with hypertropia:
Do bilateral asymmetric recessions of IR, and leave patient fusing with a slight chin up position.
Consider nasal transposition or nasal collapse of the IR (this may worsen the intorsion).
Consider superior transposition of the MR (this may worsen the intorsion).
Be aware of masked restrictions.
SO involvement can be masked by tight IR’s.
Difficult to assess the SO with FDT in the presence of tight IR’s.
SO involvement may contribute to postoperative A-pattern following IR recession.
LR involvement may give bigger than expected results with MR recession.
SR involvement may contribute to large vertical deviations.
Consider IR recession w/contralateral SR recession:
Will limit torsional effect (balancing extorter and intorter).
Will help prevent overcorrection in downgaze.
Will help correct esotropia (ET) (weakening 2 adductors).
Typically avoid resections in TED, BUT sometimes a small resection of an LR or SR is a better option than overrecession of the MR or IR, respectively.
Remember myasthenia gravis (MG) in TED patients:
STRABISMUS SURGERY AFTER SCLERAL BUCKLE (SB)
Strabismus after SB can be challenging and unpredictable.
Obtain operative report from SB procedure if possible.
Consider preoperative examination by a retina specialist to ensure that the retina is attached on the buckle and whether or not the buckle can be partially or completely removed.
If the patient is amenable, surgery on the fellow, non-SB, eye is usually easier and more predictable.
If there is significant restriction in the eye with the SB, then surgery on the buckled eye may be necessary.
Results are unpredictable so consider use of adjustable sutures (see chapter 48).
Be prepared for anatomic challenges:
Conjunctival scarring makes access and closing challenging.
Expect adhesions between muscles and between the muscle and the buckle.
The buckle may be located where the muscle should attach.
The muscle tissue overlying the buckle may be friable, increasing the risk of muscle damage or slippage (see Chapter 54).
The sclera around the implant may be thin, impacting where and how deep scleral passes are made:
Increased risk of muscle slippage (see Chapter 54).
Increased risk of scleral perforation (see Chapter 54).
Sensory challenges (see Chapter 56):
Fusion may be disrupted.
The patient may have torsion.
The muscle and buckle can be thoroughly exposed and cleaned, and sutures and the muscle can be passed underneath the buckle and be permanently attached or left for adjustment. If using this technique on an adjustable suture, be sure that the muscle slides well under the buckle (Fig. 59.2).
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