**4. Horizontal concomitant deviations**

complications are concerns of the chapter. Our hope is that this book chapter will help surgeons

The actions of the extraocular muscles and the relative contributions of each muscle to the various ocular positions are important to understand for planning surgery. The muscles act

The horizontal recti have only one primary action, while the vertical and obliques each have three actions, which vary depending on the horizontal position of the eye. The relative strengths of these actions depend upon the direction of gaze. In abduction, the vertical muscles

The superior rectus acts as an intortor in extreme adduction, but in abduction, intorsion is lost and exchanged by its elevating primary function. The inferior rectus acts as an extorter when

The superior oblique acts as an intortor, depressor, and abductor. It is the principal intortor of the eye produced by the anterior fibers of the tendon. The posterior fibers mediate depression. In adduction, it becomes a pure depressor; in abduction, it is a pure intortor. The inferior oblique acts as extorter, elevator, and abductor. It is the principal extorter of the eye. In extreme

These muscles act in concert with cooperation between ipsilateral and contralateral groups of muscles, abiding Sherrington's and Hering's laws. Sherrington's law of reciprocal innervation describes that contraction of a muscle is accompanied by relaxation of its ipsilateral antagonist muscle ensuring smooth movements of the eye. Hering's law of equal innervation regards binocular movements and explains that equal contractions occur in the muscles that are contralateral synergists and ensures that equal movements of the two eyes occur, if both

The indications for strabismus surgery fall into two categories: binocular function and cosmetic appearance with psychosocial impact. The indication and surgical goal should be based on the patients need prior to surgery and direct the surgical plan in order to achieve a successful result. Therefore, prior to surgery, the strabismus surgeon needs to establish the treatment goals by asking "Why are we operating"? Is it to establish binocular fusion, eliminate diplopia, expand the field of binocular vision, correct a compensatory head position, or improve

Signs of binocular fusion potential include intermittent strabismus, acquired strabismus, binocular fusion after neutralizing the deviation with prisms, child <2 years old, equal vision,

have a vertical action only, but in adduction, they become tortors of the eye.

the eye is in adduction; when the eye is abducted, it acts as a pure depressor.

adduction, it becomes a pure elevator; in abduction, it is a pure extortor.

**3. Surgical indication and planning for success**

of diverse experience and improve the care of strabismus patients.

**2. The actions of the extraocular muscles**

250 Advances in Eye Surgery

together in order to produce smooth eye movements.

muscles are normal.

cosmetic appearance?

Concomitant eso- and exodeviations are deviations with full ductions and the same deviation in all fields of gaze. Many horizontal deviations have an accommodative element.

Different horizontal concomitant strabismus types require different considerations when planning for successful strabismus surgery outcome and are therefore important to diagnose exactly. A table guide in planning strabismus surgery is given in Table 1. The numbers have been derived from Parks, with professor Dr. Kenneth Wright's personal modifications according to the professors own surgical experience [11, 13]. The measurement recommended is only for concomitant deviations and should be altered based on the surgeon's personal results.



a When a lateral rectus resection is done for residual esotropia after a large medial rectus recession (6 mm or larger), these numbers should be lowered.

b Avoid large LR recessions if lateral incomitance is present.

c If the horizontal angle is greater for near deviation than distance deviation, relatively more should be done to the me‐ dial rectus than the lateral rectus and vice versa.

**Table 1.** Surgical numbers

For angles >50, diopters perform bilateral surgery to more than 2 horizontal recti. This three muscle surgeries may be planned for the primary operation. The amount of surgery may be judged from the above tables. In adults, adjustable suture technique is recommended, placed on the eye where two muscles are being operated.

Strabismus can be congenital or develop later in life giving rise to different consideration for correct surgical strategy to choose. In the following, we will describe how to handle the most common strabismus types of early and later onset strabismus.

#### **4.1. Infantile esotropia (congenital esotropia)**

**Binocular surgery**

252 Advances in Eye Surgery

**Monocular surgery**

*Esotropia*

*Exotropia*

a

b

c

these numbers should be lowered.

**Table 1.** Surgical numbers

Avoid large LR recessions if lateral incomitance is present.

dial rectus than the lateral rectus and vice versa.

**MR OU Recession LR OU resectiona**

**LR OU recessionb MR OU resection**

**MR recession LR resectionb**

**LR recessionb MR resection**

When a lateral rectus resection is done for residual esotropia after a large medial rectus recession (6 mm or larger),

If the horizontal angle is greater for near deviation than distance deviation, relatively more should be done to the me‐

40<sup>Δ</sup> 5.5 mm 7.0 mm 50<sup>Δ</sup> 6.0 mm 8.0 mm

<sup>Δ</sup> 4.0 mm 3.0 mm <sup>Δ</sup> 5.0 mm 4.0 mm <sup>Δ</sup> 6.0 mm 5.0 mm <sup>Δ</sup> 7.0 mm 5.5 mm <sup>Δ</sup> 7.5 mm 6.0 mm <sup>Δ</sup> 8.0 mm 6.5 mm <sup>Δ</sup> 9.0 mm 7.0 mm

<sup>Δ</sup> 3.0 mm 3.5 mm <sup>Δ</sup> 3.5 mm 4.0 mm <sup>Δ</sup> 4.0 mm 5.0 mm <sup>Δ</sup> 4.5 mm 5.5 mm <sup>Δ</sup> 5.0 mm 6.0 mm <sup>Δ</sup> 5.5 mm 6.5 mm <sup>Δ</sup> 6.0 mm 7.0 mm

<sup>Δ</sup> 4.0 mm 3.0 mm <sup>Δ</sup> 5.0 mm 4.0 mm <sup>Δ</sup> 6.0 mm 4.5 mm <sup>Δ</sup> 6.5 mm 5.0 mm <sup>Δ</sup> 7.0 mm 5.5 mm <sup>Δ</sup> 7.5 mm 6.0 mm <sup>Δ</sup> 8.5 mm 6.5 mm

*Esotropia*

*Exotropia*

Infantile esotropia is an esotropia present during the first 6 months of life. This includes several types, with the most common being: small angle neonatal esotropia, accommodative infantile esotropia, Ciancia's syndrome, and congenital esotropia. The latter is described below.

The etiology of congenital esotropia is unknown, but genetic aspects are suspected. Congenital esotropia (CE) is characterized by a large angel constant esotropia of 40 PD or more (Figure 1) and later developing motor dysfunctions, including inferior oblique overaction (IOOA) (60%), dissociated vertical deviation (DVD) (40%), and latent nystagmus (40%). Low hyper‐ metropia is often present in an extent not giving indication for glasses. Amblyopia is present in 50% of patients with CE, however vision screening in childhood may lower this occurrence as described by Høeg et al. [17]. Smooth pursuit asymmetry is also often present as described by Wright [14]. Spontaneous resolution is rare (<4%), as shown by the Congenital Esotropia Observational Study (CEOS) if the angle is stable or increasing [6], which makes congenital esotropia a surgical disease requiring strabismus surgery.

**Figure 1.** Infantile esotropia

**Figure 2.** Ciancia's syndrome

#### *4.1.1. The management and preoperative evaluation*

The management and preoperative evaluation includes examination of the following:


The timing of surgery for congenital esotropia is controversial, as no randomized clinical controlled trials have never been conducted due to ethical aspects and low incidence. There‐ fore, different approaches are used in different continents. In the United States, early surgery (before 2 years of age) is performed routinely when the CEOS [6,7] parameters are present (i.e., angle ≥ 40 PD esotropia, constant, or increasing) supported by Wiesel and Hubel's [10] famous study regarding binocular interaction in the striate cortex of kittens reared with artificial squint that showed loss of binocular cells. In addition, most references recommend that surgery should be performed between 6 months and 1 year of age in order to achieve peripheral fusion and low-grade stereo acuity. Furthermore, one of the authors reported results from very early surgery showing high-grade stereo acuity after surgical correction between 3 and 4 months of age [15].

The surgical procedure of choice depends on age, fusion potential, and visual acuity. Bilateral medial rectus (MR) muscle recession using the near deviation as the target angle is the preferred strategy in infants without amblyopia. Patients with irreversible dense amblyopia should have monocular surgery on the amblyopic eye (recession-tightening procedure) to avoid surgical risk to the sound eye.

The goal of surgery is to align the eyes early to within 8 to 10 PD to stimulate the development of binocular fusion, as described by Dr. Marshall Parks. Larger esotropia will not allow binocular fusion. Therefore, a residual esotropia of 10 PD or larger should be considered for further treatment. The standard surgical chart (Appendix I) numbers are designed to give infants with possible fusion potential a slight immediate overcorrection (5–10 PD exotropia). This is desired as fusional convergence will pull the eyes together to become straight, fusing the small exotropia. However, patients with poor prognosis for binocular fusion (e.g., older patients >2 years old, and patients with dense irreversible amblyopia 20/50 or worse) due to long-standing congenital esotropia should be considered for surgery based on cosmetic indications. In these older patients with poor fusion potential, the surgeon should aim to slightly undercorrect and leave an esotropia of 6 to 8 PD. Using the chart numbers will correctly result in a desired slight undercorrection in older patients with poor fusion potential that predisposes to drift outward to exotropia with time. Therefore, the surgical chart numbers can be used for all patients as they self-adjust for age and fusion potential. In general, patients older than 2 years with uncorrected infantile esotropia have a poorer prognosis for binocular fusion. Even older patients, however, will occasionally show an outcome of good binocular function and some degree of stereo acuity; this could be caused by an inaccurate anamnesis.

*4.1.1. The management and preoperative evaluation*

254 Advances in Eye Surgery

nerve palsy, and infantile myasthenia gravis.

used as the surgical measure.

avoid surgical risk to the sound eye.

age [15].

**2.** Versions, to evaluate the presence of IOOA and V patterns

the full hypermetropic correction, surgery is indicated.

The management and preoperative evaluation includes examination of the following:

**1.** Ductions, which often has a mild limitation of abduction (-1), with intact abduction saccades shown by doll head maneuver or vestibular stimulation. If limited abduction and abduction saccadic movement, consider following differential diagnosis listed by decreasing incidence: Ciancia's syndrome with abduction deficiency and compensatory head turn (Figure 2), Duane's syndrome, congenital fibrosis syndrome, congenital VI

**3.** Amblyopia, which is revealed by strong fixation preference for one eye. Treat amblyopia before surgery by patching the dominant eye 4 h per day and follow-up every 1 to 2 weeks for small kids under 1 year (longer interval for older kids typically in Europe), until the patient holds fixation with the nondominant eye. The patients' cross-fixates usually

**4.** Deviation size by prism alternate cover test at near and distance deviations if possible, verified by Krimsky testing. The near deviation measure is most reliable and therefore

**5.** Cycloplegic refraction using cyclopentolate 1% one or two doses, 5 min apart, followed by refraction 30 min after last dose. If the cycloplegic refraction shows >+3.00 sphere, then prescribe the full hypermetropic correction. Repeat the cycloplegia if fluctuating readings is found on retinoscopy. After wearing the full correction constantly for 1 month, evaluate the patient for fixation preference. If an esodeviation of >10 PD persists after prescribing

The timing of surgery for congenital esotropia is controversial, as no randomized clinical controlled trials have never been conducted due to ethical aspects and low incidence. There‐ fore, different approaches are used in different continents. In the United States, early surgery (before 2 years of age) is performed routinely when the CEOS [6,7] parameters are present (i.e., angle ≥ 40 PD esotropia, constant, or increasing) supported by Wiesel and Hubel's [10] famous study regarding binocular interaction in the striate cortex of kittens reared with artificial squint that showed loss of binocular cells. In addition, most references recommend that surgery should be performed between 6 months and 1 year of age in order to achieve peripheral fusion and low-grade stereo acuity. Furthermore, one of the authors reported results from very early surgery showing high-grade stereo acuity after surgical correction between 3 and 4 months of

The surgical procedure of choice depends on age, fusion potential, and visual acuity. Bilateral medial rectus (MR) muscle recession using the near deviation as the target angle is the preferred strategy in infants without amblyopia. Patients with irreversible dense amblyopia should have monocular surgery on the amblyopic eye (recession-tightening procedure) to

indicate the absence of amblyopia, unless strong fixation preference is present.

Residual esotropia of at least 10 PD first repeat the cycloplegic refraction and prescribe the full hypermetropic correction if 1.5 sphere or more to correct ET to within 10 PD. If there persists a residual ET of 15 PD or more after prescribing glasses, then consider further surgery. If the primary surgery was bilateral MR recession of 5 mm or less, both medial rectus muscles can be further recessed. However, if the primary bilateral MR recessions were >5 mm, both lateral recti would be resect with reduced standard numbers of 1.5 mm to avoid consecutive exotropia, which is a common occurrence after LR resections for residual esotropia.

Consecutive exotropia of ≥ 15 PD that does not improve over 2–3 months may be surgically corrected. If there is full ductions, slipped medial rectus muscle is ruled out and bilateral medial rectus recession should be performed. If there is limited adduction, slipped muscle or stretch scar of the medial rectus muscles is suspected and should be addressed by exploring the medial muscle and advancing the muscle if it is found to be slipped using nonabsorbable suture to avoid re-slippage [4].

Inferior oblique overaction (IOOA) is often bilateral and associated with IE, developing after 1.5 years of age. If significant IOOA (≥ +2) is present, a weakening inferior-graded anteriori‐ zation of the IO is indicated concurrent with the horizontal surgery, performed as a one stage surgery without modifying the amount of horizontal surgery. This IO weakening procedure reduces the V pattern, eliminates the IOOA, and reduces the dissociated vertical deviation (DVD), which will be described later in this chapter.

Prognosis for motor alignment and binocularity is good for surgical cases in hands of trained surgeons. Alignment to within 10 PD of orthotropia can be achieved in 80%. If this is achieved before 2 years of age, about 70% achieve some degree of peripheral fusion and gross stereopsis (monofixation syndrome). Very early surgery (3–4 months of age) increases the chance of binocular fusion and high-grade stereo acuity. Late surgery (after 2 years of age) minimizes the chance of obtaining binocular fusion.

#### **4.2. Acquired esotropia (accommodative esotropia)**

Acquired esotropia is a subacute emergency that requires urgent consult for two reasons: (1) fusion potential diminishes in proportion to the duration of ET while early intervention is important to restore high-grade binocular fusion. Prompt dispensing of hypermetropic spectacle correction is therefore important to correct the esotropia totally or partially and reduce the occurrence of amblyopia. (2) Acquired esotropia can be the presenting sign of intracranial (brain tumor, Arnold–Chiari malformation) or neurological disease (myasthenia gravis or chronic progressive external ophthalmoplegia) causing a sixth nerve paresis, which can be concomitant in the beginning as described by Buch Hesgaard and Vinding [1].

The most common types of acquired esotropia are the accommodative, the nonaccommoda‐ tive, the cyclic, and the sensory esotropia. These often have an intermittent beginning. More seldom acute acquired concomitant esotropia develops [1]. Only the most frequent type, i.e., accommodative esotropia, will be described. Accommodative esotropia can have an infantile onset at 2 months to 1 year of age but typically develop between 1 and 3 years of age. It is characterized by initially intermittent with progression to constant moderate to large angle of deviation (20–50 PD) associated with hypermetropia (+2.00 to +6.00 sphere). The deviation is often initially intermittent and becomes constant.

The etiology is related to hypermetropia that necessitates increased accommodation for the child to achieve a clear image. This overaccommodation results in overconvergence and esotropia, depending on the AC/A ratio and divergence amplitudes.

The goal is to establish straight eyes within 8 to 10 PD of orthotropia to stimulate binocular fusion. This can be achieved in some patients with optical correction alone, and surgery is not indicated then. The patients that do not get straight eyes wearing full hypermetropic correc‐ tion, as the child in Figure 3, needs urgent surgery. Therefore, these patients should be aggressively treated with early optical correction and surgery if indicated to avoid or treat amblyopia and stimulate binocular function in the small kids (2 months to 2 years), restore binocularity in older children (2 years to 6 years), and eliminate diplopia and regain stereo acuity in the children over 6 years of age. The younger the children the more vulnerable is the binocularity, and visibility could be lost if treatment is delayed. These authors agree with the late Dr. Marshall Parks that recent onset accommodative esotropia is an ophthalmic emergen‐ cy, and the patient should be seen at an urgent appointment.

**Figure 3.** Partially accommodative esotropia

#### *4.2.1. The management and preoperative evaluation*

**4.2. Acquired esotropia (accommodative esotropia)**

256 Advances in Eye Surgery

often initially intermittent and becomes constant.

esotropia, depending on the AC/A ratio and divergence amplitudes.

cy, and the patient should be seen at an urgent appointment.

**Figure 3.** Partially accommodative esotropia

Acquired esotropia is a subacute emergency that requires urgent consult for two reasons: (1) fusion potential diminishes in proportion to the duration of ET while early intervention is important to restore high-grade binocular fusion. Prompt dispensing of hypermetropic spectacle correction is therefore important to correct the esotropia totally or partially and reduce the occurrence of amblyopia. (2) Acquired esotropia can be the presenting sign of intracranial (brain tumor, Arnold–Chiari malformation) or neurological disease (myasthenia gravis or chronic progressive external ophthalmoplegia) causing a sixth nerve paresis, which

can be concomitant in the beginning as described by Buch Hesgaard and Vinding [1].

The most common types of acquired esotropia are the accommodative, the nonaccommoda‐ tive, the cyclic, and the sensory esotropia. These often have an intermittent beginning. More seldom acute acquired concomitant esotropia develops [1]. Only the most frequent type, i.e., accommodative esotropia, will be described. Accommodative esotropia can have an infantile onset at 2 months to 1 year of age but typically develop between 1 and 3 years of age. It is characterized by initially intermittent with progression to constant moderate to large angle of deviation (20–50 PD) associated with hypermetropia (+2.00 to +6.00 sphere). The deviation is

The etiology is related to hypermetropia that necessitates increased accommodation for the child to achieve a clear image. This overaccommodation results in overconvergence and

The goal is to establish straight eyes within 8 to 10 PD of orthotropia to stimulate binocular fusion. This can be achieved in some patients with optical correction alone, and surgery is not indicated then. The patients that do not get straight eyes wearing full hypermetropic correc‐ tion, as the child in Figure 3, needs urgent surgery. Therefore, these patients should be aggressively treated with early optical correction and surgery if indicated to avoid or treat amblyopia and stimulate binocular function in the small kids (2 months to 2 years), restore binocularity in older children (2 years to 6 years), and eliminate diplopia and regain stereo acuity in the children over 6 years of age. The younger the children the more vulnerable is the binocularity, and visibility could be lost if treatment is delayed. These authors agree with the late Dr. Marshall Parks that recent onset accommodative esotropia is an ophthalmic emergen‐

The management and preoperative evaluation includes the same examination procedures as patients with infantile esotropia, including the examination of ductions, versions, and evaluation for and treatment of amblyopia after full hypermetropic correcting spectacles is prescribed, following the same method as described previously. Then if residual esotropia persists (>10 PD), surgery is indicated. However, important additional preoperative orthoptic considerations and examinations are necessary:


Lens gradient formula:


Dev org.-Dev w lens AC/A= Lens power

For AC/A formulas, exodeviations are minus and esodeviations are plus:

Normal AC/A ratio = 4 to 5 PD/D

Example: The patient, in Figure 4, has a deviation of ET 20 with full hypermetropic correction but without extra lenses. When +3.00 lenses are placed over both eyes, as illustrated in Figure 5, the patient does not have to accommodate 3 diopter-inducing divergence so the deviation now measures ET 5. The AC/A ratio is calculated below and is 5 PD/D:

> AC/A = +20 PD – +5 PD / +3D ( ) +20 PD-5 / +3D +15 PD /+3D =5 PD/D

**Figure 4.** ET without extra lenses.

**Figure 5.** Less ET with +3.00 lenses placed over the eyes.

**3.** Test for binocularity and stereo acuity using Bagolini-striated test, Titmus, Lang, or TNO test with correcting prism bar, depending on the age of the child and level of stereo acuity present. The surgeon should aim to slightly overcorrect those patients with binocular potential but undercorrect those patients with no binocular function, e.g., long-standing acquired esotropia, which is often seen in Europe. Since accommodative esotropia is acquired, and the eyes are aligned during the early period of visual development, most patients have good binocular potential at the onset of the esotropia.

The goal is to achieve orthotropia within 10 PD of esotropia to establish high-grade stereo acuity. The surgical goal for *partially accommodative esotropia* is not to operate patients out of glasses but to achieve alignment and fusion with full hypermetropic correction. Patients having cycloplegic refraction of +2.5 sphere or more will require their hypermetropic spectacles after surgery to maintain a stable angle. Surgery is indicated if residual esotropia of >10 PD persists with full hypermetropic correction worn for 2 months. Surgery is urgent as the longer the esotropia persists, the worse the prognosis for establishing binocular fusion. For infants, distance measurements are difficult to obtain; try to get this measurement but base the surgery on the near deviation. Therefore, surgery for *infantile partially accommodative esotropia* requires bilateral medial rectus recessions augmented surgery (Wright and Bruce-Lyle 1998) using the augmented formula, i.e., for a target angle between the deviation with and without hyperme‐ tropic correction. Average the near deviation with correction and the near deviation without correction or bilateral MR recessions 5.5 mm (see Appendix I on surgical numbers). Bilateral medial rectus recessions are also the treatment of choice for partially accommodative esotropia in older children. It is recommended to use the "augmented surgery formula" developed by Professor Wright to achieve alignment. This formula have improved outcome by increasing the alignment success rate from 70% to 90% by increasing the amount of surgery [16].

For AC/A formulas, exodeviations are minus and esodeviations are plus:

now measures ET 5. The AC/A ratio is calculated below and is 5 PD/D:

+20 PD-5 / +3D

**Figure 4.** ET without extra lenses.

258 Advances in Eye Surgery

**Figure 5.** Less ET with +3.00 lenses placed over the eyes.

+15 PD /+3D =5 PD/D

Normal AC/A ratio = 4 to 5 PD/D

Example: The patient, in Figure 4, has a deviation of ET 20 with full hypermetropic correction but without extra lenses. When +3.00 lenses are placed over both eyes, as illustrated in Figure 5, the patient does not have to accommodate 3 diopter-inducing divergence so the deviation

AC/A = +20 PD – +5 PD / +3D ( )

**3.** Test for binocularity and stereo acuity using Bagolini-striated test, Titmus, Lang, or TNO test with correcting prism bar, depending on the age of the child and level of stereo acuity present. The surgeon should aim to slightly overcorrect those patients with binocular potential but undercorrect those patients with no binocular function, e.g., long-standing acquired esotropia, which is often seen in Europe. Since accommodative esotropia is acquired, and the eyes are aligned during the early period of visual development, most

patients have good binocular potential at the onset of the esotropia.

Surgery is indicated in *high AC/A ratio accommodative esotropia* if there is a significant esotropia in the distance that disrupts fusion, even if a bifocal add results in fusion at near deviation. A relatively small distance deviation and large near measurement is more difficult to manage as the near distance discrepancy tends to persists postoperatively. It is recommended to perform bilateral medial recessions using a target angle based on the augmented formula with slight reduction in the numbers to prevent consecutive exotropia at distance. The patients should be informed that bifocal spectacles may be required after surgery.

There are 3 methods for determining the target angle for partially accommodative ET. These are described in the following examples:

> Nsc ET 60 Ncc ET 40 Dsc ET 50 Dcc ET 30


on prisms over full hypermetropic correction and return in 1 week. At follow-up visit, there is no change in the deviation, after placing the 30 PD base put prism; target angle: 30 PD; surgery: BMR recessions 4.50 mm.

#### *4.2.2. Postoperative management of partially accommodative esotropia*

A residual esotropia larger than 10 PD will not allow binocular fusion and should be consid‐ ered for further treatment as described above, by repeating cycloplegic refraction, prescribe full hypermetropic correction, and if there persists a residual esotropia at distance and near deviations of >10 PD, then consider further surgery if the patient has fusion potential.

Patients with preoperative high AC/A ratio will often have a residual esotropia at near deviation after surgery. To establish fusion at near deviation, bifocal add (+2.00 to +3.00 sphere) is required if the residual esotropia at near deviation is >10 PD, but the eyes are aligned at distance.

On the other hand, if a small consecutive exotropia of >10 PD results from surgery, try reducing the hypermetropic correction but not more than +2D as this leads to alignment instability. If the exotropic angle persists more than 3 months, reoperation should be considered. If the exotropia is large and associated with even mild adduction deficit, stretched scar or slipped muscle should be suspected, and the medial muscle should be explored and advanced if there is an insertion dehiscence. Surgery plan is the same as for consecutive exotropia as described above in congenital esotropia.

#### **4.3. Exotropia (intermittent exotropia)**

The normal eye position of rest is divergent due to the divergent positioning of the orbits. Therefore, small exophorias <10 PD are considered normal and the innate fusional convergence is strong (25 PD), facilitating fusion of small exodeviations.

Intermittent exotropia is a large exophoria (usually between 20 and 40 PD) that is difficult to fuse and intermittently breaks down and manifests especially when fatigued, daydreaming, or takes sedatives or drinking alcohol. Patients with intermittent exotropia have perfect stereoacuity when aligned (phoria phase), but no stereoacuity when tropic because the patient suppress the image from the deviated eye (tropia phase). Rarely patients will see double or have ARC when tropic. This is the case in patients with late onset exotropia during late childhood or adulthood. Patients with intermittent exotropia do not get strabismuc amblyopia because they have intermittent binocular fusion with high-grade stereoacuity that provides binocular visual stimulation. Patients with intermittent exotropia can have anisometropic amblyopia with the same incidence as the general population. Approximately 80% of inter‐ mittent exotropia patients will show progressive loss of fusion control and increase in the exotropia with time.

Figures 6 and 7 show a child with intermittent exotropia and straight eyes when the deviation is fused (phoria phase), and moments later, where the patient lost concentration, fusion broke and exodeviation became manifest (tropia phase).

Principles of Strabismus Surgery for Common Horizontal and Vertical Strabismus Types http://dx.doi.org/10.5772/61849 261

**Figure 6.** Intermittent exotropia, tropia phase.

on prisms over full hypermetropic correction and return in 1 week. At follow-up visit, there is no change in the deviation, after placing the 30 PD base put prism; target angle:

A residual esotropia larger than 10 PD will not allow binocular fusion and should be consid‐ ered for further treatment as described above, by repeating cycloplegic refraction, prescribe full hypermetropic correction, and if there persists a residual esotropia at distance and near

Patients with preoperative high AC/A ratio will often have a residual esotropia at near deviation after surgery. To establish fusion at near deviation, bifocal add (+2.00 to +3.00 sphere) is required if the residual esotropia at near deviation is >10 PD, but the eyes are aligned at

On the other hand, if a small consecutive exotropia of >10 PD results from surgery, try reducing the hypermetropic correction but not more than +2D as this leads to alignment instability. If the exotropic angle persists more than 3 months, reoperation should be considered. If the exotropia is large and associated with even mild adduction deficit, stretched scar or slipped muscle should be suspected, and the medial muscle should be explored and advanced if there is an insertion dehiscence. Surgery plan is the same as for consecutive exotropia as described

The normal eye position of rest is divergent due to the divergent positioning of the orbits. Therefore, small exophorias <10 PD are considered normal and the innate fusional convergence

Intermittent exotropia is a large exophoria (usually between 20 and 40 PD) that is difficult to fuse and intermittently breaks down and manifests especially when fatigued, daydreaming, or takes sedatives or drinking alcohol. Patients with intermittent exotropia have perfect stereoacuity when aligned (phoria phase), but no stereoacuity when tropic because the patient suppress the image from the deviated eye (tropia phase). Rarely patients will see double or have ARC when tropic. This is the case in patients with late onset exotropia during late childhood or adulthood. Patients with intermittent exotropia do not get strabismuc amblyopia because they have intermittent binocular fusion with high-grade stereoacuity that provides binocular visual stimulation. Patients with intermittent exotropia can have anisometropic amblyopia with the same incidence as the general population. Approximately 80% of inter‐ mittent exotropia patients will show progressive loss of fusion control and increase in the

Figures 6 and 7 show a child with intermittent exotropia and straight eyes when the deviation is fused (phoria phase), and moments later, where the patient lost concentration, fusion broke

deviations of >10 PD, then consider further surgery if the patient has fusion potential.

30 PD; surgery: BMR recessions 4.50 mm.

distance.

260 Advances in Eye Surgery

above in congenital esotropia.

exotropia with time.

**4.3. Exotropia (intermittent exotropia)**

is strong (25 PD), facilitating fusion of small exodeviations.

and exodeviation became manifest (tropia phase).

*4.2.2. Postoperative management of partially accommodative esotropia*

**Figure 7.** Intermittent exotropia, phoria phase.

#### *4.3.1. The management and preoperative evaluation*

For the most part, the treatment of intermittent exotropia is surgical. The indication for surgery is poor fusion control. Large deviations over 20 PD will eventually need surgery as they are difficult to fuse and will increase over time.

Small to moderate exodeviations (<20 PD) are usually well controlled and do not need treatment but can temporally be treated nonsurgically, but this is rarely effective in the long term. Nonsurgical options is not effective except for convergence exercises for convergence insufficiency, which is the preferred management in that disorder. Convergence exercises consist of pencil push-ups, which improve fusional convergence for near deviation, useful for convergence insufficiency, but will not reduce the distance exodeviation. Other nonsurgical treatment options is over minus glasses and monocular occlusion. Over minus glasses reduce the exotropia by stimulating accommodative convergence, which is not well tolerated because it requires the patient to constantly overaccommodate. It can be used for small angle exotropia (<15 PD) associated with concurrent myopia. Increase myopic correction by -2.5 sphere over existing correction. Monocular occlusion by patching the dominant eye for 2 to 4 h a day has been described, but recent prospective study shows no significant effect [8].

A surgical indication is poor fusion control. If the deviation is difficult to control and becomes manifest more than 50% of waking hours, then surgery is indicated. In general, it is preferable to operate after 4 years of age. This is because a small consecutive esotropia can occur after surgery, and as young children have the ability to suppress and develop amblyopia, they can loose stereoacuity after surgery. Older children with deviations greater than 20 PD are difficult to fuse and can causes eye strain, so these patients should be considered for surgery.

#### *4.3.2. Surgical plan*

The procedure of choice for intermittent exotropia is bilateral rectus recessions. Monocular recess/resect procedures induce incomitance and cause diplopia in side gaze. A small consec‐ utive esotropia (4–8 PD) immediately after surgery is desirable as the late recurrence of the exotropia is common. This consecutive exotropia will cause diplopia but usually resolve in a few days. The standard surgical number chart (Appendix I) have this small overcorrection built in.

The pattern of the deviation is important for determining the surgical plan. Exopatterns are classified based on difference of deviation, distance deviation versus near deviation: (1) basic, (2) convergence insufficiency, and (3) divergence excess divided into pseudo and true divergence excess.

	- **a.** Pseudo (90%) tenacious fusional convergence
	- **b.** True (10%) high AC/A ratio

Tenacious fusional convergence is near convergence that persists for several minutes after monocular occlusion. Patients with pseudo divergence pattern intermittent exotropia have strong tenacious fusional convergence that "falsely" diminishes the near deviation. Patching one eye for 45 min breaks tenacious fusional convergence. If the near exodeviation increases to be similar to the distance angle, e.g., 30 PD X(T) after the patch test, this indicates pseudo divergence excess, and bilateral LR recessions with a target angle of 30 PD is indicated. If the

near exodeviation does not increase with the patch test, this indicates true divergence excess and is associated with a high AC/A ratio. Bilateral LR recessions with target angle somewhere between distance and near deviations; see example below:

Dsc X(T) 30, Nsc X(T) 15 → patch test → Nsc X(T) 15. Target angle = 20–25 PD.

Patients with true divergence excess have a high AC/A ratio, and there is a high incidence of persistent esotropia and diplopia at near after surgery. Therefore, bifocals and more than one surgery are likely, and patients should be told this preoperatively.

#### *4.3.3. Postoperative management*

A surgical indication is poor fusion control. If the deviation is difficult to control and becomes manifest more than 50% of waking hours, then surgery is indicated. In general, it is preferable to operate after 4 years of age. This is because a small consecutive esotropia can occur after surgery, and as young children have the ability to suppress and develop amblyopia, they can loose stereoacuity after surgery. Older children with deviations greater than 20 PD are difficult

The procedure of choice for intermittent exotropia is bilateral rectus recessions. Monocular recess/resect procedures induce incomitance and cause diplopia in side gaze. A small consec‐ utive esotropia (4–8 PD) immediately after surgery is desirable as the late recurrence of the exotropia is common. This consecutive exotropia will cause diplopia but usually resolve in a few days. The standard surgical number chart (Appendix I) have this small overcorrection

The pattern of the deviation is important for determining the surgical plan. Exopatterns are classified based on difference of deviation, distance deviation versus near deviation: (1) basic, (2) convergence insufficiency, and (3) divergence excess divided into pseudo and true

**1.** The basic type of intermittent exotropia is responsible for 60% and have a similar deviation distance and near deviations, e.g., Dsc X (T) 30 and Nsc X(T): 35; target angle = XT 35

**2.** Convergence insufficiency intermittent exotropia type includes patients with weak convergence with a greater esotropia for near deviation. If the eyes are straight for distance, it is best to avoid surgery and treat with convergence exercises. Convergence insufficiency is the one strabismus that can be helped by exercises, e.g., Dsc Ortho. Nsc

**3.** Note: If there is a significant X(T) >15 PD in the distance, then consider bilateral lateral rectus recessions for 5 PD more than the distance angle. Patients will require convergence

**4.** Divergence excess X(T) intermittent is when the exotropia is larger for distance than near, by at least 10 PD, e.g., N X(T) 15. D X(T) 30. There are 2 types of divergence excess:

Tenacious fusional convergence is near convergence that persists for several minutes after monocular occlusion. Patients with pseudo divergence pattern intermittent exotropia have strong tenacious fusional convergence that "falsely" diminishes the near deviation. Patching one eye for 45 min breaks tenacious fusional convergence. If the near exodeviation increases to be similar to the distance angle, e.g., 30 PD X(T) after the patch test, this indicates pseudo divergence excess, and bilateral LR recessions with a target angle of 30 PD is indicated. If the

to fuse and can causes eye strain, so these patients should be considered for surgery.

*4.3.2. Surgical plan*

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divergence excess.

bilateral LR recessions.

X(T) 30; plan: convergence exercises—no surgery.

exercises after surgery for an X(T) at near deviation.

**a.** Pseudo (90%) – tenacious fusional convergence

**b.** True (10%) – high AC/A ratio

built in.

The immediate postoperative goal of surgery for intermittent exotropia is to achieve a small consecutive esodeviation of about 5 PD esotropia; in the long term, it is common for exotropia to recur. Larger consecutive esodeviations will often require further surgery. Children under 4 years of age with a small consecutive esotropia can rapidly develop amblyopia. That is why Dr. Wright suggests to postpone surgery to after 4 years of age if possible. However, if absolutely indicated because of loss of stereoacuity, part-time (2–3 h a day) alternate eye occlusion therapy may prevent amblyopia until the esotropia resolves. In older patients, the initial consecutive esotropia causes diplopia, and therefore it is important to inform the patients that diplopia may be present for some weeks to achieve a better long-term result. Hardesty et al. [2] has suggested prescribing prism glasses in the early postoperative period to neutralize the esodeviation and leave a small esophoria to stimulate divergence. For a persistent esotropia, after a week in a patient of any age, consider prescribing base out prism glasses to eliminate the diplopia and preserve binocular fusion. Give just enough prism to allow fusion while leaving a small esophoria to build divergence. If after 4 to 6 weeks the esotropia persists, then additional strabismus surgery should be considered. Either advance the lateral rectus muscle or recess the medial rectus muscles. Consider the possibility of a slipped lateral rectus muscle if abduction is limited and the esotropia is greater for distance. If the lateral has slipped, resect the stretched scar and replace at the intended recession point.

### **5. Vertical concomitant deviations**

Vertical deviations can be caused in 3 different ways, which will be described as follows: (1) overaction of the rectus muscles, i.e., superior rectus muscles, ipsilateral dissociated vertical deviations (DVD); (2) dysfunction of the horizontal rectus muscles, i.e., pattern deviations (A and V patterns); and (3) overaction of the superior and inferior oblique muscles, i.e., primary or secondary to ipsilateral IV nerve palsy or contralateral superior rectus palsy.

All the preoperative examinations and considerations previously mentioned should be performed, but additionally two important orthoptic tests are necessary to find the correct diagnosis and plan the surgery for successful results. These tests that assist the surgeon in the diagnosis of vertical muscle weakness in patients with vertical strabismus are (1) the threestep test and (2) the Bielchowsky head tilt test.

**1.** Dr. Parks described the classical three-step test for diagnosing a cyclovertical muscle palsy. It helps to differentiate SOP from contralateral superior rectus palsy and to detect bilateral SOP and includes the following:

**Step 1.**cover test identifies which eye is hypertropic. The elevators of the low eye (IO or SR) or the depressors of the high eye (SO or IR) are affected.

**Step 2.**Side gaze to the right and left changes the degree of height. If the height increases when the eyes move away from the high eye, the possible weak muscle is either SO of the adducted eye or the contralateral SR (elevates the eye in abduction). Conversely, if the height increases when the eye move in the direction of the higher eye, it suggests either weak IR of the abducted eye (depresses the eye in abduction) or weak IO of the contralateral adducted eye.

**Step 3.**determine the hypertropia in up- and downgaze by cover test. This identifies which of the contralateral muscles is responsible for the vertical deviation. A modification to make this easier is "Wright's rule" described by Dr. Wright, which is a 2-step process: (1) Do the head tilt test first. If the hypertropia increases on head tilt to the side if the hypertropia, this indicates an oblique muscle palsy, and if the hypertropia increases opposite to the hypertropia, it is a rectus muscle palsy. (2) Test horizontal gaze to see where the hypertropia is greatest and match to the field of action of the cyclovertical muscle in question from step 1.

**2.** The Bielchowsky head tilt test helps to further identify a superior oblique weakness. When the head is tilted to the right, the right eye intorts by action of the intorters (SO and SR) of the eye, and their vertical pulls cancel each other if both are healthy. However, if the SO is weak, the moderately unopposed SR causes a hypertropia to develop in the intorting eye, as illustrated in Figure 8.

**Figure 8.** Explanation of the Bielchowsky head tilt test.

When the correct diagnosis and the weak muscle have been found, a plan for successful strabismus surgery outcome can be made by using the following five-step guideline:


#### **5.1. Dissociated vertical deviation**

**1.** Dr. Parks described the classical three-step test for diagnosing a cyclovertical muscle palsy. It helps to differentiate SOP from contralateral superior rectus palsy and to detect

**Step 1.**cover test identifies which eye is hypertropic. The elevators of the low eye (IO or SR)

**Step 2.**Side gaze to the right and left changes the degree of height. If the height increases when the eyes move away from the high eye, the possible weak muscle is either SO of the adducted eye or the contralateral SR (elevates the eye in abduction). Conversely, if the height increases when the eye move in the direction of the higher eye, it suggests either weak IR of the abducted

**Step 3.**determine the hypertropia in up- and downgaze by cover test. This identifies which of the contralateral muscles is responsible for the vertical deviation. A modification to make this easier is "Wright's rule" described by Dr. Wright, which is a 2-step process: (1) Do the head tilt test first. If the hypertropia increases on head tilt to the side if the hypertropia, this indicates an oblique muscle palsy, and if the hypertropia increases opposite to the hypertropia, it is a rectus muscle palsy. (2) Test horizontal gaze to see where the hypertropia is greatest and match

**2.** The Bielchowsky head tilt test helps to further identify a superior oblique weakness. When the head is tilted to the right, the right eye intorts by action of the intorters (SO and SR) of the eye, and their vertical pulls cancel each other if both are healthy. However, if the SO is weak, the moderately unopposed SR causes a hypertropia to develop in the intorting

When the correct diagnosis and the weak muscle have been found, a plan for successful

strabismus surgery outcome can be made by using the following five-step guideline:

eye (depresses the eye in abduction) or weak IO of the contralateral adducted eye.

to the field of action of the cyclovertical muscle in question from step 1.

bilateral SOP and includes the following:

264 Advances in Eye Surgery

eye, as illustrated in Figure 8.

**Figure 8.** Explanation of the Bielchowsky head tilt test.

or the depressors of the high eye (SO or IR) are affected.

Dissociated vertical deviation (DVD) occurs in patients with infantile esotropia and can occur with any disorder that disrupts normal binocular visual development. DVD is commonly associated with CE in Europe, where late surgery is the timing of choice. However, the incidence of surgery demanding severe DVD has dropped in the United States, probably due to early surgery with better sensory outcome. DVD is typically latent. However, when one eye is occluded (Figure 9), or when the patient is fatigued or daydreaming, it manifests, having three components: elevation, abduction, and extorsion. The vertical component is predomi‐ nant. DVD is characterized by slow drift of one eye up and out with extorsion. It is usually bilateral and asymmetric and can be distinguished from a true hypertropia by the lack of a corresponding hypotropia in the contralateral eye, when the hypertropic eye returns to primary position. The indication for surgery for DVD is primarily based on the patients psychosocial requirements.

**Figure 9.** Bilateral DVD with a right hypertropia with the right eye covered and left hypertropia with the left eye cov‐ ered.

Surgery is indicated if the deviation is larger than 10 PD, increases in frequency, and becomes obvious or symptomatic. Surgery for DVD is ipsilateral large superior rectus recession often between 5 mm to a maximum of 9 mm (fixed suture technique) as suggested by professor Dr. K. Wright.

Most cases require bilateral surgery. If the DVD is asymmetric, perform asymmetric superior rectus recessions. Unilateral surgery is indicated in patients with amblyopia >2 lines, which will not fixate with the amblyopic eye, where ipsilateral superior rectus recession is indicated. If DVD and inferior oblique overaction coexist, an inferior oblique anteriorization procedure is indicated and sufficient in most cases. Only in severe cases combined surgery of inferior oblique anteriorization and superior rectus recession is necessary. In this case, the superior rectus recession should be minimized to avoid limitation of up gaze.

#### **5.2. Pattern (A and V) deviations**

These are patterns of strabismus in which the horizontal deviation alters on upgaze and downgaze so that the pattern resembles the letter A or V and is considered significant if the horizontal angle varies by more than 10 PD (A pattern) or 15 PD (V pattern) diopters between up- and downgaze. An example of a V pattern esotropia is shown in Figure 10. The underlying cause may be as follows: (1) horizontal muscle dysfunction caused by abnormal insertion or action of the medial/lateral recti (spontaneously or secondary to surgery); (2) vertical rectus dysfunction (tight superior rectus/inferior rectus muscle weakness for A pattern and vice versa for V pattern), or (3) oblique muscles dysfunction (inferior oblique under action/superior oblique overaction for A patterns and vice versa for V patterns).

**Figure 10.** An example of a V pattern esotropia with arrow pattern.

#### **5.3. Treatment of A and V patterns**

Surgery is indicated if the deviation is larger than 10 PD, increases in frequency, and becomes obvious or symptomatic. Surgery for DVD is ipsilateral large superior rectus recession often between 5 mm to a maximum of 9 mm (fixed suture technique) as suggested by professor Dr.

Most cases require bilateral surgery. If the DVD is asymmetric, perform asymmetric superior rectus recessions. Unilateral surgery is indicated in patients with amblyopia >2 lines, which will not fixate with the amblyopic eye, where ipsilateral superior rectus recession is indicated. If DVD and inferior oblique overaction coexist, an inferior oblique anteriorization procedure is indicated and sufficient in most cases. Only in severe cases combined surgery of inferior oblique anteriorization and superior rectus recession is necessary. In this case, the superior

These are patterns of strabismus in which the horizontal deviation alters on upgaze and downgaze so that the pattern resembles the letter A or V and is considered significant if the horizontal angle varies by more than 10 PD (A pattern) or 15 PD (V pattern) diopters between up- and downgaze. An example of a V pattern esotropia is shown in Figure 10. The underlying cause may be as follows: (1) horizontal muscle dysfunction caused by abnormal insertion or action of the medial/lateral recti (spontaneously or secondary to surgery); (2) vertical rectus dysfunction (tight superior rectus/inferior rectus muscle weakness for A pattern and vice versa for V pattern), or (3) oblique muscles dysfunction (inferior oblique under action/superior

rectus recession should be minimized to avoid limitation of up gaze.

oblique overaction for A patterns and vice versa for V patterns).

**Figure 10.** An example of a V pattern esotropia with arrow pattern.

K. Wright.

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**5.2. Pattern (A and V) deviations**

If the pattern is small, not affecting fusion and not causing a compensatory head position, then it can be observed. If the pattern is significant and symptom producing, the treatment of choice is either by inducing an abnormal head posture to maintain binocular vision or by interfering with maintenance of binocular function binocular surgery. The surgical procedure depends on underlying muscle dysfunction. If the pattern is due to horizontal rectus muscle dysfunction without oblique and vertical rectus muscle dysfunction, surgery should be carried out to the horizontal rectus muscles and should be combined with recession ± resection of these muscles to treat any associated eso- or exotropia in primary position. In bilateral surgery, the surgeon needs to elevate or depress the positions of medial or lateral rectus insertions. This is done by symmetrical full tendon vertical transposition surgery to contralateral MRs or LRs. The surgeon needs to move MRs toward the apex of the pattern (upward in A pattern and downward for V pattern, i.e., in the direction of the greatest esodeviation) or LRs away from the apex of the pattern (downward for A pattern and upward for V pattern, in the direction of the greatest exodeviation), as illustrated in Figure 11. The pattern breaking effect can be increased by recessing the upper or lower margin of the appropriate transposed horizontal muscle insertion 2 mm more in the direction where more weakening is required.

**Figure 11.** Move MRs toward the apex of the pattern or LRs away from the apex of the pattern.

When unilateral recess/resect surgery is indicated, i.e., cases with unilateral amblyopia, or strabismus with equal near and distance angles, the horizontal rectus muscles are transposed elevating RL and depressing MR in V pattern and vice versa for A pattern. To increase the effect, the rectus muscles can be resutured to the globe with the upper and lower parts of the insertion placed at different distances from the limbus, e.g., place the lower margin of the medial rectus in a preferentially weaker position than upper margin, and vice versa for lateral rectus muscles in V patterns. Some authors [5] even prefer this repositioning to elevating or depressing the insertions as it reduces the risk of inducing unwanted torsion effects.

Each horizontal muscle is resected or recessed as specified by the magnitude of the horizontal deviation. Half width elevation or depression collapses pattern by 10 to 15 PD diopters. Fullwidth elevation or depression collapses pattern by up to 25 diopters. The latter is used for patterns exceeding 25 PD. Expect relatively more effect for the surgical amounts for larger pattern deviations.

If oblique overaction is present, appropriate oblique muscle surgery should be performed.

#### **5.4. Inferior oblique overaction and superior oblique palsy**

Inferior oblique overaction (IOOA) is a common form of strabismus. It can be primary (idiopathic) or secondary caused by a superior oblique palsy (SOP). The clinician can give the right diagnose by performing the head tilt test. With primary IOOA, head tilt test is negative, and with SOP, head tilt is positive.

Figure 12 shows a +3 left IOOA with left upshoot on right gaze. Right eye is fixing, allowing the left adducting eye to elevate. Bilateral IOOA is associated with a V pattern because the inferior oblique muscles are abductors in the field of action in upgaze.

**Figure 12.** IOOA left eye.

#### *5.4.1. Primary IOOA*

Primary IOOA is usually bilateral and asymmetrical. It is often associated with horizontal strabismus, typically infantile esotropia (60%), but it can occur isolated. Signs of IOOA are upshoot in adduction, V pattern, and extorsion on fundus examination. The V pattern associated with primary IOOA is a Y with little or no change in the horizontal deviation from primary to downgaze. This patient had an upgaze preference and adopted chin down posturing to obtain binocular fusion (Figure 13).

#### *5.4.2. Secondary IOOA (superior oblique palsy)*

Secondary IOOA is most commonly due to a unilateral congenital SOP and less commonly bilateral acquired SOP. Differences and characteristics of unilateral and bilateral SOP are summarized in Table 2. Since the SO muscle is a depressor, a weak SO muscle can cause an ipsilateral IOOP and hypertropia in primary. A bilateral SOP will have cancelling hypertropia, so typically there is a small or no hypertropia in primary position. The key sign of SOP is hypertropia with the hypertropia increasing on tilt to the same side as the hypertropia and hypertropia increasing on horizontal gaze opposite to the hypertropia, as shown on photos

**Figure 13.** V pattern esotropia with compensatory chin down head posture.

below. In addition, patients with unilateral SOP will adopt a compensatory head tilt opposite to the side of the SOP to facilitate binocular fusion (R-SOP compensates with tilt left). In primary IOOA, the head tilt is negative, but the extorsion can be seen on fundus exam. Patients with congenital SOP do not have subjective extorsion. However, patients with acquired SOP will experience torsional diplopia that can be measured on Maddox rod testing.


**Table 2.** Unilateral versus bilateral superior oblique paresis

#### *5.4.3. Congenital SO palsy*

patterns exceeding 25 PD. Expect relatively more effect for the surgical amounts for larger

If oblique overaction is present, appropriate oblique muscle surgery should be performed.

Inferior oblique overaction (IOOA) is a common form of strabismus. It can be primary (idiopathic) or secondary caused by a superior oblique palsy (SOP). The clinician can give the right diagnose by performing the head tilt test. With primary IOOA, head tilt test is negative,

Figure 12 shows a +3 left IOOA with left upshoot on right gaze. Right eye is fixing, allowing the left adducting eye to elevate. Bilateral IOOA is associated with a V pattern because the

Primary IOOA is usually bilateral and asymmetrical. It is often associated with horizontal strabismus, typically infantile esotropia (60%), but it can occur isolated. Signs of IOOA are upshoot in adduction, V pattern, and extorsion on fundus examination. The V pattern associated with primary IOOA is a Y with little or no change in the horizontal deviation from primary to downgaze. This patient had an upgaze preference and adopted chin down

Secondary IOOA is most commonly due to a unilateral congenital SOP and less commonly bilateral acquired SOP. Differences and characteristics of unilateral and bilateral SOP are summarized in Table 2. Since the SO muscle is a depressor, a weak SO muscle can cause an ipsilateral IOOP and hypertropia in primary. A bilateral SOP will have cancelling hypertropia, so typically there is a small or no hypertropia in primary position. The key sign of SOP is hypertropia with the hypertropia increasing on tilt to the same side as the hypertropia and hypertropia increasing on horizontal gaze opposite to the hypertropia, as shown on photos

**5.4. Inferior oblique overaction and superior oblique palsy**

inferior oblique muscles are abductors in the field of action in upgaze.

pattern deviations.

268 Advances in Eye Surgery

**Figure 12.** IOOA left eye.

*5.4.1. Primary IOOA*

posturing to obtain binocular fusion (Figure 13).

*5.4.2. Secondary IOOA (superior oblique palsy)*

and with SOP, head tilt is positive.

Congenital SO palsy is usually unilateral with a relatively large hypertropia (10–30 PD), which is intermittently binocular fused so the eyes appear well aligned, facilitated by a compensatory head tilt and face turn away from the hypertropia. Therefore, facial asymmetry is common with the smaller side opposite to the SO palsy, as shown in Figure 14.

Patients with congenital SO palsy usually have excellent stereoacuity and have exaggerated vertical fusion amplitudes, and they can fuse large hyperdeviations up to 25 to 30 PD, whereas

**Figure 14.** Congenital SOP, compensatory head tilt, and face turn away from the hypertropia.

normal vertical fusion amplitudes are at 2–3 PD. The hypertropia will manifest when the patient is fatigued, much like patients with intermittent exotropia. When tropic, patients usually suppress diplopia, but some will note double vision. There is usually a significant IOOA with minimal under action of the SO. The etiology of congenital SO palsy is unknown, but some cases have been associated with a lax or absent SO tendon (rare).

Patients typically have control over the deviation in younger age, but as fusional control weakens over time, they may present late even as senior adults with intermittent vertical strabismus and manifest the hyperdeviation when they are fatigued. Typically, patients with decompensated congenital SO palsy present with large HT in primary with the HT increasing on head tilt to the affected side and in gaze to the contralateral side (Figures 15–19). Patients with intermittent vertical strabismus, facial asymmetry, and long-standing head tilt, which can be documented on early childhood family photos, have congenital SOP until proven otherwise. Unfortunately, patients with congenital SO palsy are misdiagnosed and receive multiple consultations, CT, MRI scans, and even surgery for the torticollis. Avoid this by knowing the 7 key findings of congenital SOP, which are as follows: (1) large vertical fusion amplitudes, (2) ipsilateral IO overaction, (3) positive head tilt (>hyper on tilt to the hyper), (4) torticollis (compensatory head tilt opposite to SOP), (5) minimal or no vertical diplopia before it decompensates, (6) no torsion on Maddox rod, and (7) facial asymmetry.

**Figure 15.** Congenital SO palsy with large RHT in primary with the RHT increasing on head tilt right and in left gaze (R-IOOA).

Principles of Strabismus Surgery for Common Horizontal and Vertical Strabismus Types http://dx.doi.org/10.5772/61849 271

**Figure 16.** Congenital SO palsy with large RHT in primary with the RHT increasing on head tilt right and in left gaze (R-IOOA).

normal vertical fusion amplitudes are at 2–3 PD. The hypertropia will manifest when the patient is fatigued, much like patients with intermittent exotropia. When tropic, patients usually suppress diplopia, but some will note double vision. There is usually a significant IOOA with minimal under action of the SO. The etiology of congenital SO palsy is unknown,

Patients typically have control over the deviation in younger age, but as fusional control weakens over time, they may present late even as senior adults with intermittent vertical strabismus and manifest the hyperdeviation when they are fatigued. Typically, patients with decompensated congenital SO palsy present with large HT in primary with the HT increasing on head tilt to the affected side and in gaze to the contralateral side (Figures 15–19). Patients with intermittent vertical strabismus, facial asymmetry, and long-standing head tilt, which can be documented on early childhood family photos, have congenital SOP until proven otherwise. Unfortunately, patients with congenital SO palsy are misdiagnosed and receive multiple consultations, CT, MRI scans, and even surgery for the torticollis. Avoid this by knowing the 7 key findings of congenital SOP, which are as follows: (1) large vertical fusion amplitudes, (2) ipsilateral IO overaction, (3) positive head tilt (>hyper on tilt to the hyper), (4) torticollis (compensatory head tilt opposite to SOP), (5) minimal or no vertical diplopia before it

**Figure 15.** Congenital SO palsy with large RHT in primary with the RHT increasing on head tilt right and in left gaze

but some cases have been associated with a lax or absent SO tendon (rare).

**Figure 14.** Congenital SOP, compensatory head tilt, and face turn away from the hypertropia.

decompensates, (6) no torsion on Maddox rod, and (7) facial asymmetry.

(R-IOOA).

270 Advances in Eye Surgery

**Figure 17.** Congenital SO palsy with large RHT in primary with the RHT increasing on head tilt right and in left gaze (R-IOOA).

**Figure 18.** Congenital SO palsy with large RHT in primary with the RHT increasing on head tilt right and in left gaze (R-IOOA).

**Figure 19.** Congenital SO palsy with large RHT in primary with the RHT increasing on head tilt right and in left gaze (R-IOOA).

Masked bilateral SOP can look like a unilateral SOP as only one eye will show significant IOOA. The presence of a V-pattern and bilateral extorsion on fundus examination also suggests bilateral involvement in patients with a presumed unilateral SOP. In these cases of masked bilateral SOP, if surgery is performed on one eye, the contralateral SOP will become evident postoperatively

#### *5.4.4. Traumatic SO palsy*

Traumatic SO palsy is caused by closed head trauma. It is almost always bilateral as the 4th nerves exit the brain close together, so both nerves get traumatized with a traumatic shift of the tentorium. Since the strabismus is acquired, patients complain of torsional, vertical, and horizontal diplopia, worse in downgaze (SO field of action). Because both SO muscles are weak, the verticals cancel each other so there is minimal to no hypertropia in primary position. These patients have significant torsional diplopia because there is bilateral extorsion, which can be seen on fundus exam and on double Maddox rod testing. The fundus photos will show bilateral extorsion with the foveae below the lower pole of the optic disc. The pattern of strabismus for bilateral SO palsy is reversing hypertropia: (1) RHT on tilt right and LHT on tilt left and (2) RHT in left gaze and LHT on right gaze and a V pattern with esotropia in downgaze (Table 3).


**Table 3.** Example of measurements of bilateral SOP.

Bilateral SOP has a characteristic V pattern that is an arrow subtype. Since the SO muscles are abductors in downgaze, bilateral SOP causes lack of abduction in down gaze, thus causing an esotropia in downgaze. This causes a V-arrow pattern because most of the eso-shift occurs from primary position to downgaze. The big eso-shift from primary position to downgaze typical of an arrow pattern, which is virtually pathognomonic for bilateral SOP, as shown in Figure 10.

#### *5.4.5. The management of inferior oblique muscle dysfunction*

Selection of the appropriate surgical procedure is based on the amount of inferior oblique dysfunction. Inferior oblique overaction is clinically estimated on a scale of +1 through +4. Quantify the upshoot by bringing the fixing eye straight across to the lateral canthus and observe the adducting eye for upshoot (Figure 20).

Quantification of upshot in inferior oblique overaction: the abducting eye is fixating. The adducting eye is free to manifest the overaction. (A) Minimal upshoot (+1). (B) Upshoot (+2) of the adducting eye is obvious when the abducting eye looks straight across the lateral Principles of Strabismus Surgery for Common Horizontal and Vertical Strabismus Types http://dx.doi.org/10.5772/61849 273

**Figure 20.** Quantifying the IOOA on a scale of +1 through +4.

Masked bilateral SOP can look like a unilateral SOP as only one eye will show significant IOOA. The presence of a V-pattern and bilateral extorsion on fundus examination also suggests bilateral involvement in patients with a presumed unilateral SOP. In these cases of masked bilateral SOP, if surgery is performed on one eye, the contralateral SOP will become evident

Traumatic SO palsy is caused by closed head trauma. It is almost always bilateral as the 4th nerves exit the brain close together, so both nerves get traumatized with a traumatic shift of the tentorium. Since the strabismus is acquired, patients complain of torsional, vertical, and horizontal diplopia, worse in downgaze (SO field of action). Because both SO muscles are weak, the verticals cancel each other so there is minimal to no hypertropia in primary position. These patients have significant torsional diplopia because there is bilateral extorsion, which can be seen on fundus exam and on double Maddox rod testing. The fundus photos will show bilateral extorsion with the foveae below the lower pole of the optic disc. The pattern of strabismus for bilateral SO palsy is reversing hypertropia: (1) RHT on tilt right and LHT on tilt left and (2) RHT in left gaze and LHT on right gaze and a V pattern with esotropia in

**Tilt R–RH 12 Tilt L–LH 10 R-gaze** Ortho **L-gaze** LH 8 RH 4 RH 10 ET 10

Bilateral SOP has a characteristic V pattern that is an arrow subtype. Since the SO muscles are abductors in downgaze, bilateral SOP causes lack of abduction in down gaze, thus causing an esotropia in downgaze. This causes a V-arrow pattern because most of the eso-shift occurs from primary position to downgaze. The big eso-shift from primary position to downgaze typical of an arrow pattern, which is virtually pathognomonic for bilateral SOP, as shown in

Selection of the appropriate surgical procedure is based on the amount of inferior oblique dysfunction. Inferior oblique overaction is clinically estimated on a scale of +1 through +4. Quantify the upshoot by bringing the fixing eye straight across to the lateral canthus and

Quantification of upshot in inferior oblique overaction: the abducting eye is fixating. The adducting eye is free to manifest the overaction. (A) Minimal upshoot (+1). (B) Upshoot (+2) of the adducting eye is obvious when the abducting eye looks straight across the lateral

postoperatively

272 Advances in Eye Surgery

*5.4.4. Traumatic SO palsy*

downgaze (Table 3).

Figure 10.

**Table 3.** Example of measurements of bilateral SOP.

*5.4.5. The management of inferior oblique muscle dysfunction*

observe the adducting eye for upshoot (Figure 20).

canthus. (C) Severe upshoot (+3) of adducting eye. (D) Very severe upshoot (+4) of adducting eye.

The basic rule of thumb is that patients with +2 or more IOOA are candidates for an inferior oblique surgery, and those with +1 or less can be followed except those with significant V pattern (>15 PD). These should be considered for IO weakening procedure even with only +1 IOOA. In cases of asymmetric overaction, bilateral surgery should be done, even when one eye only displays +1 overaction, to avoid unmasking the minimal overaction. If amblyopia is present (greater than 2 Snellen lines), it is safer to restrict surgery to the amblyopic eye. Monocular surgery is sufficient in these amblyopic cases as the sound eye is always fixing and will not manifest an upshoot.

Weakening procedure of the IO muscle is the treatment for IO overaction, that is, IO recession (Figure 21), myectomy (Figure 22), or anteriorization (Figure 23). Inferior oblique overaction can be reduced by surgically moving the insertion anterior toward the equator and nasally so it is closer to the inferior rectus muscle (see the red arrow in the drawing below). Moving IO insertion nasally toward the inferior rectus slackens the IO, thus weakening its function and is called an IO recession. Myectomy weakens the inferior oblique, as removing a portion of muscle reduces the chance of local reattachment. Moving the IO insertion anterior to the equator changes the IO from an elevator to more of a depressor, and this is called IO anterior transposition. The graded anteriorization procedure is the authors' procedure of choice for mild to severe inferior oblique overaction. The basis of the graded anteriorization procedure is that the more anterior the inferior oblique insertion, the greater the weakening effect, tailoring the amount of IOOA to the amount of anteriorization. The IO muscle is placed 4 mm posterior to the inferior rectus insertion for +1 IOOA, and 3 to 4 mm to IR for +2 IOOA, 1 to 2 mm to IR for +3 IOOA, and at IR insertion for +4 IOOA. Severe bilateral DVD and IOOA needs the "J" deformity full anteriorization of the entire IO insertion, including the posterior fibers. The "J" deformity limits elevation of the eye.

**Figure 21.** Recession.

**Figure 22.** Myectomy.

**Figure 23.** Anteriorization.

In general, avoid antielevation by keeping the IO muscle 2 mm posterior to the IR insertion and avoid "J" deformity by keeping the IO posterior fibers posterior, as described in detail at the end of this chapter.

The final surgical decision must be based on a combination of factors, including the amount of V pattern and the presence of a vertical deviation in primary position. If no vertical deviation is present in primary position, then consider symmetrical surgery. Asymmetric-graded anteriorization is indicated if a hypertropia is present, and more anteriorization of the IO should be done on the side of the hypertropia. A full anteriorization (at the IR insertion, without "J" deformity) corrects about 6 PD hypertropia. An anteriorization with "J" deformity can correct up to 18 PD of hypertropia.

#### *5.4.6. The management of congenital superior palsy*

**Figure 21.** Recession.

274 Advances in Eye Surgery

**Figure 22.** Myectomy.

**Figure 23.** Anteriorization.

Surgery is indicated for a significant head tilt, a hypertropia causing asthenopia, and symp‐ tomatic diplopia. The surgery timing is controversial. In the United States, early surgery is suggested to prevent secondary facial asymmetry, while otters advocate waiting until 2 to 3 years of age. Late surgery is advocated in Europe as strabismus measures are more reliable and binocular function more mature and stable. There is no evidence to clearly choose, as no controlled clinical randomized trials have ever been conducted. The authors' advice is to wait until 2 years of age as long as the head tilt is mild, or if binocular fusion is compromised, early surgery is indicated.

Prisms are usually of limited value because of the incomitance, but in some older adults, prisms can be used to help control the deviation. If prisms are used, undercorrect the deviation to stimulate vertical fusion amplitudes.

The surgical plan depends on the pattern of the strabismus, depending on unilateral or bilateral location. In general, the treatment strategy is based on where the deviation is greatest and designing a surgical plan to correct the deviation in the primary position while reducing the incomitance.

Unilateral SOP with hypertropia <18 PD can be treated with graded anteriorization ipsilateral IO muscle. Unilateral hypertropia >18 PD can be treated by graded anteriorization, ipsilateral IO muscle, and contralateral IR recession (if there is significant hyper in down gaze). Bilateral SOP with hypertropia <8 PD can be treated by bilateral IO-graded anteriorization with greater anteriorization on the hypertropic side. A masked bilateral can be treated by ipsilateral IO anteriorization and contralateral IR recession plus contralateral IO recession. If there is residual head tilt after IO weakening procedure, perform the Harada–Ito procedure on the opposite side to the head tilt. SO tendon tuck is reserved for extreme lax SO tendon.

#### *5.4.7. The management of traumatic superior oblique paresis*

Observe conservatively for at least 6 months, taking serial measurements of the deviation. If, after 6 months of observation, the SOP persists with diplopia, surgery should be considered. Prism glasses are usually not useful because of the torsion and incomitance of the deviation.

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