Evaluation and management of strabismus in children

INTRODUCTION — Strabismus is the condition of misalignment of the eyes. Strabismus can be horizontal, vertical, torsional, or a combination of these.

The evaluation and management of strabismus in children will be reviewed here. The causes of strabismus are discussed separately. (See "Causes of horizontal strabismus in children" and "Causes of vertical strabismus in children".)

TERMINOLOGY — The terms used to describe strabismus depend upon the direction of eye deviation, the conditions under which it is present, and whether it changes with the position of gaze.

The prefix of the term describes the direction of eye deviation (figure 1):

●"Eso" − Deviation nasally (inward) relative to the fixating eye

●"Exo" − Deviation temporally (outward) relative to the fixating eye

●"Hyper" – Upward deviation

●"Hypo" − Downward deviation

The suffix of the term describes the conditions under which it is present:

●"Phoria" − Latent strabismus (ie, present only when binocular fusion is disrupted, such as when one eye is covered).

●"Tropia" − Manifest strabismus (ie, present when there is no disruption of binocular fusion). Manifest strabismus can be constant or intermittent, occurring only when fusional capabilities are exceeded (eg, when the child is tired) [1]. Manifest strabismus can be uniocular (deviation always involves the same eye) or alternating (either eye may deviate).

Other terms:

●"Comitant" – Deviation is the same size in all positions of gaze.

●"Incomitant" – Deviation size is different depending upon the position of gaze. This type of eye deviation is characteristic of paralytic or restrictive strabismus, though it can be present in other forms of strabismus.

FUNCTIONS OF EXTRAOCULAR MUSCLES — There are six extraocular muscles for each eye (figure 2). These muscles work together to move the eyes vertically, horizontally, and torsionally. The functions of the extraocular muscles are as follows (table 1):

●The medial rectus is responsible for adduction

●The lateral rectus is responsible for abduction

●The superior rectus is primarily responsible for supraduction (upward vertical movement)

●The inferior rectus is primarily responsible for infraduction (downward vertical movement)

●The superior oblique is primarily responsible for incyclotorsion

●The inferior oblique is primarily responsible for excyclotorsion

●The vertical rectus muscles and the oblique muscles have secondary and tertiary functions as well (table 1)

The superior oblique muscle is innervated by cranial nerve IV (the trochlear nerve), the lateral rectus muscle by cranial nerve VI (the abducens nerve), and all the others by cranial nerve III (the oculomotor nerve) (table 1).

The understanding of strabismus requires knowledge of the two major principles that govern ocular motility [2]:

●Hering's law of equal innervation − Agonist muscles in both eyes receive equal innervation to ensure coordinated binocular eye movements. For example, when the right lateral rectus muscle is activated to abduct the right eye, the left medial rectus muscle is equally activated to adduct the left eye.

●Sherrington's law of reciprocal innervation − Agonist/antagonist muscle pairs within each eye receive reciprocal innervation [3]. For example, when the right medial rectus muscle contracts to adduct the right eye, its ipsilateral antagonist, the right lateral rectus muscle, relaxes.

The cardinal positions of gaze isolate the yoke muscles, which allows the examiner to identify specifically which extraocular muscle(s) are causing the strabismus (figure 3).

EPIDEMIOLOGY — Strabismus occurs in approximately 2 to 4 percent of the population [4-6]. Risk factors for strabismus include [7-12]:

●Family history of strabismus.

●Preterm birth and/or low birth weight.

●Other ocular conditions – Conditions that predispose to strabismus include [13,14]:

•Vision deprivation (eg, retinopathy of prematurity, corneal scars, cataracts, severe ptosis, and longstanding vitreous hemorrhage)

•Hyperopia

•Anisometropia

•Amblyopia

•Impairment of binocular fusion

Strabismus can even be a presenting sign of retinoblastoma when it involves the fovea and thus causes vision deprivation in an eye [15]. (See "Retinoblastoma: Clinical presentation, evaluation, and diagnosis", section on 'Clinical presentation'.)

●Certain neuromuscular conditions (eg, cerebral palsy, muscular dystrophy). (See "Cerebral palsy: Classification and clinical features", section on 'Vision problems' and "Duchenne and Becker muscular dystrophy: Clinical features and diagnosis".)

CAUSES — Congenital and acquired causes of strabismus are summarized in the table (table 2) and discussed in detail separately:

●(See "Causes of horizontal strabismus in children".)

●(See "Causes of vertical strabismus in children".)

MIMICS OF STRABISMUS — In infants, true strabismus must be differentiated from pseudostrabismus and ocular instability of infancy.

●Pseudostrabismus – Pseudoesotropia is the most common form of pseudostrabismus. It is the false appearance of eye crossing that most commonly occurs in infants and children with a wide nasal bridge and/or large epicanthal folds during the first few years of life. It is an optical illusion in which the wide nasal bridge or epicanthal folds cover the nasal sclera, making the eye appear esotropic, particularly when the child looks in lateral gaze (picture 1). Normal ocular alignment is demonstrated by symmetric corneal light reflexes and the cover and cover/uncover tests. The use of a diagram may help in explaining the concept of pseudoesotropia to parents/caregivers [16]. (See 'General physical examination' below.)

Pseudoexotropia also can occur. Pseudoexotropia is most commonly seen in children with temporal dragging of the macula secondary to retinal traction. Retinopathy of prematurity is the most common cause of pseudoexotropia. Other causes include vascular abnormalities, choroiditis, macular scars, and other peripheral retinal disorders that cause traction (eg, familial exudative vitreoretinopathy, toxocara retinitis, incontinentia pigmenti) [17]. As with pseudoesotropia, pseudoexotropia can be differentiated from true strabismus with the cover/uncover test and alternate cover test. (See 'General physical examination' below.)

Pseudostrabismus can also be caused by orbital deformities or tumors that cause dystropia but not true strabismus.

●Ocular instability of infancy – This refers to the unsteady ocular alignment that is often present in normal newborns during the first few months of life [18]. It is characterized by intermittent exo or eso deviation of the eyes and typically is not seen after four to six months of age.

EVALUATION — Pediatric health care providers can detect strabismus with several simple clinical tests. It is most important to detect manifest deviations because they have greater potential to cause amblyopia, a functional reduction in the visual acuity of an eye caused by disuse or misuse during the critical period of visual development. Latent deviations are rarely associated with amblyopia. In addition, it is important to rule out causes of sensory strabismus that can be life-threatening (eg, retinoblastoma); after leukocoria, esotropia is the most common presenting sign of retinoblastoma [15]. (See "Amblyopia in children: Classification, screening, and evaluation", section on 'Definition' and "Retinoblastoma: Clinical presentation, evaluation, and diagnosis", section on 'Clinical presentation'.)

History — When evaluating a child with ocular misalignment, the history focuses on characterizing the symptoms and identifying an underlying cause (table 2). Questions to ask include:

●What is the developmental/birth history?

●Is there a family history of strabismus?

●Has the deviation been present since early infancy?

●Is there any history of head or eye trauma?

●Are there any other medical problems (eg, neuromuscular or genetic disorders)?

●Is there a history of exposure to toxins or medications?

●What is the duration and severity of the deviation?

●When is the deviation present? (eg, constant or intermittent? with fatigue? only in certain positions of gaze?)

●Are there other symptoms (headaches, abnormal head posture, diplopia, asthenopia [eye strain])?

●Does the child complain of double vision or behave as though double vision may be present (closing one eye, misjudging objects, etc)?

General physical examination — The physical examination should include assessment of general health and neurologic status, including an assessment of development. The presence of abnormal head posture (eg, tilt or turn) should be noted. The presence of an anomalous head posture is suggestive of paralytic, restrictive, or pattern strabismus.

Eye examination — The primary care provider's ophthalmologic examination should include assessment of visual function, pupillary reactivity, eyelid position, and extraocular movements (ductions/versions), as well as the corneal light reflex test, the cover test, and the and cover/uncover test [19].

Corneal light reflex — The corneal light reflex test, also called the Hirschberg test, often is used as an initial screen for strabismus. In this test, an accommodative target (eg, a small toy) is held several feet in front of the child's face and a penlight is held next to the toy. If ocular alignment is normal, the light reflex is positioned centrally and symmetrically in each eye (figure 4). Deflection of the corneal light reflex in one eye is noted if a moderate to large ocular misalignment is present. Each millimeter of deflection is associated with approximately 7 to 10 degrees of deviation [20]. Because the corneal light reflex test can overlook small deviations, it should be used in conjunction with the cover test and the cover/uncover test.

Cover test — The cover test is one of the most important tests used in the detection of manifest strabismus (tropia). In this test, the child is asked to visually fixate on a target at distance or near. The examiner briefly covers one eye while observing the opposite eye for movement. If the child has normal ocular alignment, no movement is detected when covering either eye (orthotropia). Manifest strabismus (tropia) is present if the eye that is not occluded with the cover test shifts to refixate on the target when the fellow previously fixating eye is covered. The test should be repeated on each eye. The child should be referred to a pediatric ophthalmologist if manifest strabismus is detected.

Cover/uncover test — The cover/uncover test is used to detect latent strabismus (phoria). If the cover test detects a tropia, the primary care provider need not perform additional testing with the cover/uncover test, since the abnormal cover test alone is sufficient basis for referral to an ophthalmologist. In the cover/uncover test, the child is asked to visually fixate on a target at distance or near. A cover is placed over one eye for a few seconds, and then it is rapidly removed. The eye that was under the cover is observed for refixation movement. If a phoria is present, this previously covered eye will shift back into the orthotropic (straight-ahead) position to reestablish sensory fusion with the other eye. If such movement is detected, latent strabismus is present (figure 5). Latent strabismus is held in check by ocular fusion. Small, barely perceptible phorias are common and not pathologic. Large phorias can be associated with asthenopia (eye strain) and diplopia and should be evaluated by an ophthalmologist.

Brückner test — The Brückner test, also known as the simultaneous red reflex test, is another test that is useful in detecting small-angle strabismus [21,22]. In this test, the examiner positions himself or herself 18 to 20 inches away from the child's face and uses a direct ophthalmoscope with the largest diameter of light to view both of the child's red reflexes simultaneously. The lenses on the ophthalmoscope are adjusted until the skin around the eyes is in focus, and the child's attention is directed at a target adjacent to the direct ophthalmoscope. This permits both pupillary red reflexes to be examined at the same time. They should be identical in size, shape, color, and brightness (figure 6).

The child should be referred to a pediatric ophthalmologist if a difference in size, shape, color, or brightness between the two eyes is noted. Asymmetry of the red reflexes on Brückner testing may indicate a serious ocular disorder, including strabismus, significant anisometropia (imbalance of refractive error), or media opacity that is obstructing the visual axis (eg, cataract, anterior chamber or vitreous disorder, coloboma, or retinal tumor) [19]. (See "Approach to the child with leukocoria", section on 'Referral'.)

Additional evaluation — The need for further evaluation depends upon the suspected etiology of strabismus. Blood tests (including complete blood count, erythrocyte sedimentation rate, or C-reactive protein) and/or neuroimaging studies may be indicated but are rarely required for routine strabismus. Neuroimaging studies should be considered in children with craniofacial malformations, neurologic disorders, findings on neurologic examination, head or orbit trauma, or acute onset of paralytic or restrictive strabismus. (See "Causes of horizontal strabismus in children" and "Causes of vertical strabismus in children".)

INDICATIONS FOR REFERRAL — Infants and children should be referred for ophthalmologic evaluation if any of the following are present [23]:

●Constant strabismus at any age

●Intermittent manifest strabismus after four to six months of age

●Persistent esodeviations after four months of age

●Corneal light reflex test or cover test demonstrating a strabismic deviation

●Asymmetry of the pupil appearance (size, shape, color, and brightness) on the Brückner simultaneous red reflex test (figure 6)

●Deviation size that changes depending upon the position of gaze (incomitant strabismus)

●Torticollis that is not explained on a musculoskeletal basis (see "Acquired torticollis in children")

●Complaints of diplopia or asthenopia (eye fatigue with near work [ie, reading])

●Parental concern about ocular alignment

The ophthalmologist's examination should be comprehensive and include cycloplegic refraction to determine if there is a need for refractive correction. This is especially important in esotropia to rule out accommodative esotropia.

COMPLICATIONS — The complications of strabismus include:

●Amblyopia (occurs in up to one-half of younger children with strabismus). (See "Amblyopia in children: Classification, screening, and evaluation" and "Amblyopia in children: Management and outcome".)

●Diplopia (in acquired strabismus in patients typically ≥4 years old).

●Secondary contracture of the extraocular muscles, limiting extraocular motility and binocular visual fields; secondary contracture may develop over a course of weeks to months if a strabismus that is associated with a fixation preference for one eye is not treated.

●Adverse psychosocial and vocational consequences [24-28].

OVERVIEW OF MANAGEMENT — The treatment for strabismus depends upon the etiology. General principles of strabismus management are reviewed below. Additional aspects of treatment in specific strabismus types are discussed separately:

●Idiopathic infantile esotropia (see "Causes of horizontal strabismus in children", section on 'Idiopathic infantile esotropia')

●Accommodative esotropia (see "Causes of horizontal strabismus in children", section on 'Accommodative esotropia')

●Hypo- and hyperdeviations (see "Causes of vertical strabismus in children")

Improved ocular alignment and binocularity (including stereopsis) are the goals of therapy [29]. A trial of nonsurgical intervention may precede surgical therapy in some cases.

Vision impairment — The initial management of strabismus addresses vision impairment caused by amblyopia. Therapy may include the refractive error correction with glasses or contact lenses and/or occlusion therapy or pharmacologic or optical penalization of the preferred eye. In addition, surgical procedures may be required to correct conditions that obstruct the visual axis (eg, cataract, ptosis, hemangioma). (See "Refractive errors in children", section on 'Optical correction' and "Amblyopia in children: Management and outcome" and "Cataract in children", section on 'Management'.)

Alignment — Management strategies for strabismus include observation with regular follow-up or medical and surgical approaches. Observation with regular follow-up by an ophthalmologist is appropriate for children in whom the deviation is small (ie, <5 to 8 degrees), intermittent, and moderately or well controlled, and in whom fusion or stereopsis can be demonstrated.

Both surgical and nonsurgical interventions are used to correct ocular alignment [30].

●Nonsurgical therapies – Nonsurgical therapies include the prescription of spectacles and/or contact lenses, prism therapy, miotic drops to manipulate accommodation, occlusion therapy, and visual training exercises (orthoptics).

●Surgery – Surgical procedures to improve ocular alignment include recession, resection, and transposition of the extraocular muscles and a variety of other procedures that are beyond the scope of this topic review.

•Extraocular muscle recession involves repositioning of the muscle insertion posterior to the original insertion on the sclera, which effectively weakens its effect on globe position.

•Extraocular muscle resection involves shortening the muscle, which permits it to act as a passive restraint, effectively increasing its effect on globe position.

●Postoperative recovery – As a general rule, recovery from strabismus surgery is rapid and serious complications are rare. Nausea and vomiting are not uncommon on the first postoperative day and sometimes require treatment with antiemetics. Pain is typically mild and can be managed with acetaminophen or ibuprofen. A small amount of blood-tinged discharge from the operated eye(s) for the first two to four days is normal. Postoperative subconjunctival hemorrhage and conjunctival injection typically resolve by two to three weeks after surgery. Temporary double vision may be experienced by some patients.

●Postoperative complications – Temporary diplopia is not uncommon but typically resolves after a few days. Less commonly, bacterial conjunctivitis can occur postoperatively; it is typically mild and readily clears with topical antibiotics. More serious postoperative infections, preseptal cellulitis and endophthalmitis, are rare. Warning signs of infection include marked chemosis and injection of the conjunctiva and lids, decreased vision, purulent discharge, and occasionally severe pain. Children who develop these findings should be seen by the ophthalmologist emergently. (See "Bacterial endophthalmitis".)

INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5^th to 6^th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10^th to 12^th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.

Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)

●Basics topic (see "Patient education: Crossed eyes and lazy eye (The Basics)")

SUMMARY AND RECOMMENDATIONS

●Definition – Strabismus is the term used to describe an anomaly of ocular alignment. Strabismus can occur in one or both eyes and in any direction. (See 'Introduction' above and 'Terminology' above.)

●Functions of extraocular muscles – There are six extraocular muscles in each eye that are responsible for eye movement (figure 2 and table 1). Evaluation of the cardinal positions of gaze helps the examiner isolate which extraocular muscle(s) are causing the strabismus (figure 3). (See 'Functions of extraocular muscles' above.)

●Causes – Causes of strabismus are summarized in the table (table 2) and discussed in detail separately. (See "Causes of horizontal strabismus in children" and "Causes of vertical strabismus in children".)

●Mimics of strabismus – Ocular instability of infancy is frequently present in healthy newborns during the first few months after birth. Pseudostrabismus is also common in the first year of life. Pseudoesotropia is the false appearance of eye crossing caused by a wide nasal bridge or epicanthal folds obscuring the nasal sclera (picture 1). Normal ocular alignment is demonstrated by the corneal light reflex and the cover and cover/uncover tests. (See 'Mimics of strabismus' above.)

●History – Important aspects of the history include developmental/birth history; family history of strabismus; onset of deviation (eg, early infancy); history of head or eye trauma; other medical problems (eg, neuromuscular or genetic disorders); exposure to toxins or medications; duration and severity of the deviation; whether the deviation is constant or intermittent and, if intermittent, what exacerbates it (eg, fatigue, positions of gaze); and other symptoms (headaches, abnormal head posture, diplopia, eye strain). (See 'History' above.)

●General examination – Important aspects of the primary care provider's physical examination include assessment of general health and neurologic status and the presence of abnormal head posture. (See 'General physical examination' above.)

●Eye examination

•By the primary care provider – The primary care provider's eye examination should include an assessment of visual function, pupillary reactivity, eyelid position, extraocular movements (ductions/versions), corneal light reflex test (figure 4), cover test, cover/uncover test (figure 5), and the Brückner simultaneous red reflex test (figure 6).

•By the ophthalmologist – The ophthalmologist's examination should be comprehensive and include cycloplegic refraction to determine if there is a need for refractive correction. This is especially important in esotropia to rule out accommodative esotropia. (See 'General physical examination' above.)

●Referral – Indications for ophthalmologic referral include (see 'Indications for referral' above):

•Constant strabismus at any age

•Intermittent manifest strabismus after four to six months of age

•Persistent esodeviations after four months of age

•The corneal light reflex test or cover test demonstrates deviation

•Asymmetry of appearance on the Brückner simultaneous red reflex test (figure 6)

•Deviation that changes depending upon the position of gaze (incomitant strabismus)

•Torticollis that is not explained on a musculoskeletal basis (see "Acquired torticollis in children")

•Complaints of diplopia or asthenopia (eye fatigue with near work [ie, reading]) or signs that diplopia is present (tendency to keep one eye closed)

•Parental concern about ocular alignment

●Complications – Complications of strabismus include amblyopia, diplopia, secondary contracture of the extraocular muscles, and adverse psychosocial and vocational consequences. (See 'Complications' above.)

●Management – The treatment for strabismus depends upon the etiology. The goals of treatment are improved ocular alignment and binocularity (including fusion and stereopsis). (See 'Overview of management' above.)