This form of esotropia is present within the first six months of life. Generally, the amount of crossing, or angle of deviation, is large, measuring 15 degrees or more. The classic pattern is one of cross fixation, where objects to the right side are viewed with the left eye, and vice versa. This condition is a syndrome of likely associated conditions. The crossing of the eyes is the earliest manifest and the most obvious. Other features tend to present somewhat later, and include over or underaction of oblique muscles. The most common of these—present in about 75% of children with infantile esotropia—is over action of the inferior oblique muscle, and is recognized in side gaze. The eye looking toward the nose elevates higher than the opposite eye. When present bilaterally, a “V” pattern is present, meaning the eyes are more crossed in down gaze than up. Less commonly, overaction of the superior obliques—with over depression of the eye looking toward the nose—will result in an “A” pattern, meaning the eyes are more crossed in up gaze than down. In addition to oblique muscle dysfunctions, there is a tendency for one eye to drift upwardly and sometimes outwardly, a condition known as Dissociated Vertical Deviation (or DVD). These movements tend to occur if amblyopia (decreased vision in one eye) is present, and when affected persons are tired, ill or inattentive. These additional portions of the syndrome may require additional surgery, after correction of the initial crossing. Other features of the infantile esotropia syndrome are more variable and include amblyopia, for which patching may be required, and latent nystagmus (rhythmic or irregular, dancing or shaking movements of the eyes), for which no treatment is likely required or possible. Generally the first indicated operation for infantile esotropia is recession of the medial rectus muscle of each eye.  

Accommodative esotropia is acquired somewhat later in childhood, typically age two to five years, and is treated with eyeglasses. Many children with this condition will also require patching of the dominant eye to improve vision in the crossing (or amblyopic) eye. In certain individuals, eyeglasses, even eyeglasses with bifocals, will not fully correct the crossing. In these cases, surgery is generally performed to correct the crossing that is not corrected by wearing glasses. Attempts to correct all crossing, including that corrected by glasses, may be misguided in young children, because to the degree that these children will outgrow their farsightedness, they will partially outgrow the need for their glasses. In effect, doing enough surgery to correct all crossing may increase the likelihood that children will need further surgery for over correction, or outward deviation of the eyes (consecutive exotropia). Generally, the first indicated operation for partially accommodative esotropia is recession of one or more medial rectus muscle(s). 

Exotropia refers to eyes that drift apart, one eye staying centered, while the other drifts to the outside or toward the temple. Affected persons will often squint one eye closed (generally the eye that drifts), especially in bright light or when tired or performing prolonged near visual tasks. The usual pattern, no matter the age of onset, is intermittency. One eye will drift apart at times of fatigue, if the person is ill, “under the influence”, or even daydreaming. It is generally more noticed when looking at the distance, rather than near. It will typically self-correct if attention is called to the deviation, or if a near object is viewed. Progression is typically manifested by an increase in the frequency and duration of the deviation. The total angle of deviation usually is an individual matter, and does not increase over time. The principal functional risk is the loss of binocular vision. The condition becomes symptomatic (increased eye strain and fatigue) with age. Double vision is not usually a prominent symptom, although it can be intermittently bothersome while driving, especially at night. Think of this problem as essentially being a problem of an abnormal, divergent position of rest of the eyes; that is, the eyes will tend to drift apart when effort is not being or able to be made to control the divergent angle. This is not a condition that typically self-corrects. While patching in very young children (under the age of two), eyeglasses with prisms (for small deviations in older persons who wear glasses) and convergence exercises (for older children and adults with small deviations who wish to try and will be compliant) may have some benefit, that benefit is often temporary and typically does not fundamentally change the position of rest. Surgery is the one modality that will change that position. Although conditions may vary, surgery is indicated when the condition is progressive and seen every day. While there is no emergency, there is typically no particular benefit to deferring surgery, once the indication for it is secure. However, delay will generally not cause an adverse outcome unless the deviation has become constant. Typically, the initial procedure performed is recession of one or both lateral recti.

In general, poor vision in infancy causes the eyes to converge; thereafter, if poor vision occurs in one eye, that eye will drift outwardly. This is known as sensory exotropia. Sometimes surgery performed for crossed eyes (esotropia) overcorrects the condition and the eyes drift outwardly. This is known as consecutive exotropia. One special form of this condition occurs when there is slippage of a muscle, typically the previously operated nose side, or medial rectus muscle. The muscle may not adequately attach to the eye and therefore be disinserted; alternatively, the muscle may gradually slip within its capsule (or sleeve) or gradually stretch/elongate with time, called a slipped or stretched muscle. When this occurs the opposing muscle, typically the lateral rectus muscle, contracts and becomes overly tight. For these conditions, surgery is often performed only on the affected eye and may consist of a recession of the lateral (or temple side) muscle, with or without a resection (tightening) of the medial (nose side) rectus muscle. When slipping, stretching or disinsertion of a muscle is suspected, that muscle generally explored and reattached at the appropriate place. The “appropriate place” is generally dictated by findings at the time of surgery and guided by the judgment of an experienced strabismus surgeon. If a muscle is detached and “lost” (unable to be retrieved and typically a medial rectus muscle), pulling force may be borrowed from other muscles in the form of a transposition of all or some of the vertical (superior and inferior) rectus muscles. Sometimes such decisions must be made at the time of surgery, and your surgeon will explain and ask for your prior permission to do the appropriate thing based on findings at surgery. Your doctor will share, and you should understand the range of possibilities ahead of time; in part this is to permit your surgeon the latitude to do the proper procedure.

Vertical misalignment of the eyes may be present and equal in all fields of gaze, called a comitant deviation. More frequently, vertical misalignment ia greater in one or a few fields of gaze, called an incomitant deviation. Three variations are described below.

These conditionsmay be effectively treated in a number of ways. One common approach is to recess the muscle; and the recession may be graded in response to the degree of overaction. Despite some potential limitations, some surgeons prefer to sever the muscle (myotomy) or remove a portion of the belly of the muscle (myectomy). If dissociated vertical deviation is present, a recession of the muscle may be modified to transpose the insertion of the muscle forward (called and anterior transposition); this operation serves the dual purpose of weakening the overacting muscle while holding the eye down against the tendency to drift upward. It is often preferred as the primary inferior oblique procedure in the context of infantile esotropia. If over action of the inferior oblique is persistent, despite anterior transposition of the muscle, a nasal myectomy of the muscle may be performed. In very rare circumstances—where there is absence of the opposing superior oblique, in selected instances of extreme over action of the inferior oblique and under action of the superior oblique, and large torsional deviations—anterior and nasal transposition of the inferior oblique may be performed. A few surgeons will remove the muscle entirely for extreme over action of the muscle; however, this is an operation of last resort because it forecloses any other surgical options on the oblique (as above). When the muscle is under acting or weak, its antagonist (superior oblique) may be weakened to balance the forces (please see below).

Over action of the superior oblique has lead to a number of techniques to weaken the superior oblique that mimic similar operations on the inferior oblique. The anatomy differs in that the surgery is performed only on the reflected tendon and not muscle. The most commonly performed weakening procedure is either severing the tendon (tenotomy) or removing a segment of the tendon (tenectomy). When good binocular vision is present with stereopsis, a posterior partial tenectomy may be performed. In other cases, to preserve binocular function in the face of marked over action or tightness (for example, Brown’s Syndrome), the tendon may be lengthened by placement of a silicone spacer. Some recommend a recession of the superior oblique tendon. 

When weakness, or under action, of the superior oblique is present, the tendon may be tucked (or imbricated); alternatively, the antagonist muscle (inferior oblique) may be weakened as above.

All strabismus surgery outcomes are improved with good technique; and this is particularly meaningful in the context of oblique muscle surgery, particularly the superior oblique. It is the most challenging type of surgery to perform properly.

When there is over or under action of the vertical rectus muscles (superior and inferior), a vertical imbalance occurs. These muscles may be tight, such as in inferior rectus fibrosis, thyroid eye disease involving muscles or fibrosis following injection with local anesthetic during cataract or other surgery under local anesthesia. In these cases the muscles act like a leash, mechanically restricting full motion of the eyes. Treatment is directed at releasing the leash or restrictive effect, generally by recession of the affected “tight” muscle. 

Less commonly, as in conditions such as Dissociated Vertical Deviation, the muscles may apparently overact. In this condition, one may consider either recession of the superior rectus (to weaken vertical movement) or resection of the inferior rectus (to hold the eye down).

One relatively common vertical muscle misalignment is caused by weakness of the trochlear (or fourth cranial nerve). In this case the muscle is receiving inadequate enervation from its brain stem nerve. The condition may be congenital (meaning present at or around birth, whether or not it is hereditary) or acquired, particularly as a consequence of closed head trauma. The most common strategy is to weaken the antagonist inferior oblique muscle, as above. In severe cases, particularly congenital fourth nerve palsy with a large head tilt, the superior oblique muscle may be tucked.

If a person assumes an abnormal position of the head, it may be secondary to a number of ocular conditions. There are a few eye problems that cause abnormal head positions. Strabismus may cause tilting of the head toward one shoulder, turning the face to one side (to turn the eyes in the opposite horizontal direction, e.g., face right for eyes left), and/or elevating or depressing the chin (to turn the eyes in the opposite vertical direction, e.g., cgin up for eyes down). In the above conditions, one or more of these compensatory positions may be assumed. 

Duane’s Syndrome comes in three types, and if abnormal head positions are assumed, the usual direction is a horizontal turn of the face; there also may be associated vertical up and down shoots of the eyes observed. To change the head position, depending on the type, either recession of the medial (usually) or lateral rectus (less commonly) muscle is appropriate. 

In Brown’s syndrome, the malpositioning of the head usually involves a chin up position, in an effort to avoid pulling against a tight superior oblique tendon. Tendon lengthening with silicone spacer is a commonly performed procedure. 

In fourth nerve palsy, the head position is more complicated, with head tilt, turn and chin depression combined; a long standing head position can lead to developmental changes in the face, with hypertrophy (overgrowth, or enlargement) f one side of the face. As noted above, a common procedure is to recess the antagonist inferior oblique muscle; in large or long-standing deviations, recession of one or more vertical rectus muscle(s) on either eye may be added or substituted for the foregoing.

Nystagmus is a special case. Some children will have calming of the motions of the eyes in one position, called the null point. The null point is a neurologically driven phenomenon, and the head positioning is a strategy to achieve the best possible vision. Improved vision is a powerful driver of a head position in these children. Nystagmus surgery is designed to move the head by moving the neurological null point to a place closer to or at straight ahead. Generally, large amounts of surgery on multiple muscles are required to move the eyes—and their null point—to a different position. A common procedure performed for this condition is the so-called Kestenbaum procedure, where simultaneous recession and resection procedures of large amounts are performed on the appropriate medial and lateral rectus muscles. The purpose is to move the eyes in the direction of the face turn, and away from the preoperative gaze (or eye) position.

Thyroid eye disease typically has three components: protrusion or bulging of the eyes, retraction of the eyelids (making the protrusion appear more prominent), and strabismus. The strabismus is the result of low grade inflammation of the extraocular muscles. Imaging studies may show thickening of the muscles. As a consequence of the inflammation there is stiffening, restriction and retraction of the muscles. With retraction, the eyes are pulled out of alignment. The most commonly involved muscles are the medial and inferior rectus muscles, although any may be involved. The most common operation performed is recession of one or more of the affected muscles. Eye muscle surgery may make retraction and bulging of the eyes more noticeable. Thyroid eye disease can be difficult to manage, as the condition may progress or change, and with it the alignment of the eyes; consequently additional operations are frequently required on eye muscles and eye lids.

• iinjuries that sever or lead to swelling of and hemorrhage into the muscle,
• injection of local anesthetics such as those used in cataract surgery,
• injuries to muscles during other surgery such as sinus drainage and plastic surgical procedures, and
• so-called “blow out” fractures of the orbit (bony socket in which the eye sits).

The first challenge in trauma is to carefully define the problem, its extent and effects. Imaging studies, such as computed tomography (CT) and magnetic resonance imaging (MRI), may be appropriate. 

If strabismus occurs, particularly with diplopia, initial steps should involve primary repair (if appropriate and possible) of the original injury. After swelling has diminished and healing of the injury has occurred, strabismus surgery may be indicated. In general, the effects of injury cause scarring and restriction of eye movements, and therefore surgery is directed at releasing the restriction to permit alignment. Like some other complicated strabismus problems, the surgery is intended to improve the condition, but may, and likely will not completely reverse the effects of the original insult. Consequently, “perfect” outcomes are rare, and multiple surgeries may be required.

The most common “complication” of eye muscle surgery is that the first procedure did not effectively align the eyes, either short or long term. There are reasons for this. First, the “problem” of primary (no obvious cause) strabismus is complex, involving multiple areas of the brain. Simplistically, one may say that it is “caused” by and abnormal pattern of nerve impulses sent from eye movement centers at the base of the brain. Current knowledge cannot contemplate “rearranging” these brain centers, and thus treatment is directed to the end organs, or eye muscles. In effect, we have a mechanical solution to a complex neuromuscular interaction. There is bound to be (and there is) significant imprecision in achieving desired effects. Second, the outcome of surgery is substantially related to the potential for binocular vision. If it can be established, or retrieved, long-term motor (or physical) alignment is more likely to be achieved and sustained.; and not vice versa. And thirdly, anticipated effects and improvements are derived from experience. That experience is derived from performing similar procedures on prior patients with the same condition of the same degree. How a given person will respond to that experience has a statistical variation that is only partially related to technique. Much of the variation is carried as a fact of nature in the human specie. For some, multiple procedures are required to achieve desired alignment. Only general statements may be made about the likelihood of needing additional surgery: complicated strabismus, neurological problems, and absence of binocular potential are risk factors for additional procedures.

The bottom line message is that reoperations are commonly necessary, either for over/ under corrections or for new problems that may arise. Bear in mind that, for most conditions, additional surgery is generally available and effective (within the above bounds). For most individuals, odds accumulated in their favor; meaning that (complicating factors notwithstanding) additional surgery carries a positive expectation of outcome.

Congenital malformations involving abnormalities in the formation or position of eye muscles are at once uncommon and challenging. Often, these problems accompany others, such as craniofacial malformations. Two examples are rotation of the eye muscles (so that they do not pull in the anticipated directions), and absence of the superior oblique tendon/ muscle. Imaging studies such as a computed tomographic (CT) scan can assist your surgeon is designing an appropriate approach.

New knowledge about the anatomy and function of orbital tissues, including muscles, is emerging. Aided by detailed magnetic resonance imaging (MRI), specialized elements of muscles and their surrounding attachments (called “pulleys”) are gaining better understanding. Early basic information is beginning to be clinically applied to an emerging understanding of the potential role of these microstructures in clinical strabismus. This information holds significant promise for the future, particularly in complicated forms of adult strabismus.

Doctors Beauchamp and Mitchell are pediatric ophthalmologists and strabismologists (quite a mouthful!), practicing respectively in Dallas/ Fort Worth, Texas and Hartford, Connecticut. They are members of the American Ophthalmological Society and were trained in the specialty at Children’s National Medical Center in Washington, DC. Both are actively involved in clinical practice, teaching and research.

Dr. Beauchamp is Professor of Clinical Ophthalmology at the University of Texas Southwestern Medical Center, Dallas and in clinical practice. He serves as Chairman of the Board of the National Children’s Eye Care Foundation, Director at Large of the American Association for Pediatric Ophthalmology and Strabismus and Chair of its Outcomes and Policy Committee. He has previously served as Chairman of the Ethics Committee of the American Academy of Ophthalmology and Director of the American Board of Ophthalmology.