Strabismus

Overview

Definition

Strabismus is the misalignment of the eyes in any direction (vertical, horizontal). Colloquially, it is referred to as “crossed eyes.”

Classification

Strabismus can be classified as:

• Infantile
• Acquired

Medical terminology describes the direction of eye deviation:

• Horizontal strabismus:
  • Esotropia: inward (nasal) deviation of the eye
  • Exotropia: outward (temporal) deviation of the eye
• Vertical strabismus:
  • Hypertropia: upward deviation of the eye
  • Hypotropia: downward deviation of the eye

Other considerations:

• A “-tropia” is detectable with both eyes Both Eyes Refractive Errors open:
  • May be constant or intermittent
  • Can affect one or both eyes Both Eyes Refractive Errors
• A “-phoria” describes latent strabismus that is present only when 1 eye is covered (e.g., esophoria).

Epidemiology

• Prevalence Prevalence The total number of cases of a given disease in a specified population at a designated time. It is differentiated from incidence, which refers to the number of new cases in the population at a given time. Measures of Disease Frequency in the United States: 
  • 2%–5% of the population
  • 5 million–15 million people
• Affects boys and girls equally
• Age:
  • Infantile esotropia typically starts at < 6 months of age. 
  • Intermittent esotropia can present at any age. 

Etiology

Most strabismus results from an abnormality of the neuromuscular control of eye movement. Less commonly, there is a problem with the extraocular muscles.

• Infantile strabismus:
  • Familial in approximately 30% of children
  • Idiopathic Idiopathic Dermatomyositis
  • Preterm birth Preterm birth Preterm labor refers to regular uterine contractions leading to cervical change prior to 37 weeks of gestation; preterm birth refers to birth prior to 37 weeks of gestation. Preterm birth may be spontaneous due to preterm labor, preterm prelabor rupture of membranes (PPROM), or cervical insufficiency. Preterm Labor and Birth and/or low birth weight
  • Family history Family History Adult Health Maintenance of strabismus
  • Genetic disorders (e.g., Down syndrome Down syndrome Down syndrome, or trisomy 21, is the most common chromosomal aberration and the most frequent genetic cause of developmental delay. Both boys and girls are affected and have characteristic craniofacial and musculoskeletal features, as well as multiple medical anomalies involving the cardiac, gastrointestinal, ocular, and auditory systems. Down syndrome (Trisomy 21))
  • Prenatal drug exposure
  • Congenital Congenital Chorioretinitis eye defects
• Acquired strabismus:
  • Uncorrected refractive errors Refractive errors By refraction, the light that enters the eye is focused onto a particular point of the retina. The main refractive components of the eye are the cornea and the lens. When the corneal curvature, the refractive power of the lens, does not match the size of the eye, ametropia or a refractive error occurs. Refractive Errors
  • Cranial nerve palsy Palsy paralysis of an area of the body, thus incapable of voluntary movement Cranial Nerve Palsies:
    • 3rd cranial nerve (oculomotor palsy Palsy paralysis of an area of the body, thus incapable of voluntary movement Cranial Nerve Palsies)
    • 4th cranial nerve ( superior oblique Superior oblique Orbit and Extraocular Muscles: Anatomy palsy Palsy paralysis of an area of the body, thus incapable of voluntary movement Cranial Nerve Palsies)
    • 6th cranial nerve ( lateral rectus Lateral rectus Orbit and Extraocular Muscles: Anatomy palsy Palsy paralysis of an area of the body, thus incapable of voluntary movement Cranial Nerve Palsies)
  • Neurologic conditions:
    • Cerebral palsy Palsy paralysis of an area of the body, thus incapable of voluntary movement Cranial Nerve Palsies
    • Spina bifida
    • Hydrocephalus Hydrocephalus Excessive accumulation of cerebrospinal fluid within the cranium which may be associated with dilation of cerebral ventricles, intracranial. Subarachnoid Hemorrhage
    • Encephalitis Encephalitis Encephalitis is inflammation of the brain parenchyma caused by an infection, usually viral. Encephalitis may present with mild symptoms such as headache, fever, fatigue, and muscle and joint pain or with severe symptoms such as seizures, altered consciousness, and paralysis. Encephalitis/ meningitis Meningitis Meningitis is inflammation of the meninges, the protective membranes of the brain, and spinal cord. The causes of meningitis are varied, with the most common being bacterial or viral infection. The classic presentation of meningitis is a triad of fever, altered mental status, and nuchal rigidity. Meningitis
    • Brain Brain The part of central nervous system that is contained within the skull (cranium). Arising from the neural tube, the embryonic brain is comprised of three major parts including prosencephalon (the forebrain); mesencephalon (the midbrain); and rhombencephalon (the hindbrain). The developed brain consists of cerebrum; cerebellum; and other structures in the brain stem. Nervous System: Anatomy, Structure, and Classification tumors
    • Stroke (the leading cause of adult strabismus)
    • Multiple sclerosis Sclerosis A pathological process consisting of hardening or fibrosis of an anatomical structure, often a vessel or a nerve. Wilms Tumor
  • Can be a presenting sign of retinoblastoma Retinoblastoma Retinoblastoma is a rare tumor but the most common primary intraocular malignancy of childhood. It is believed that the condition arises from a neuronal progenitor cell. Retinoblastoma can be heritable or non-heritable. Retinoblastoma
  • Head injuries
  • Graves’ disease Graves’ disease A common form of hyperthyroidism with a diffuse hyperplastic goiter. It is an autoimmune disorder that produces antibodies against the thyroid stimulating hormone receptor. These autoantibodies activate the TSH receptor, thereby stimulating the thyroid gland and hypersecretion of thyroid hormones. These autoantibodies can also affect the eyes (Graves ophthalmopathy) and the skin (Graves dermopathy). Thyrotoxicosis and Hyperthyroidism

Pathophysiology

• During forward gaze, both eyes Both Eyes Refractive Errors normally fixate on an object together.
• Regulated by the 6 extraocular muscles 
• These 6 extraocular muscles operate under: 
  • Hering’s law of equal innervation: equal innervation occurs through synergistic agonist muscles in both eyes Both Eyes Refractive Errors.
  • Sherrington’s law of reciprocal innervation: ↑ innervation to a muscle is accompanied by an equal ↓ in innervation to the antagonist muscle.
• Any process that results in a deviation from these results in strabismus.

Clinical Presentation

Strabismus presents as:

• Misalignment of the eyes: 
  • Unilateral or bilateral 
  • Intermittent or constant
• Manifest strabismus: evident without covering the eye
• Latent strabismus: evident only with the eye-cover test
• Diplopia Diplopia A visual symptom in which a single object is perceived by the visual cortex as two objects rather than one. Disorders associated with this condition include refractive errors; strabismus; oculomotor nerve diseases; trochlear nerve diseases; abducens nerve diseases; and diseases of the brain stem and occipital lobe. Myasthenia Gravis:
  • Vertical (present in vertical strabismus) 
  • Horizontal (present in horizontal strabismus) 
• Amblyopia (↓ vision Vision Ophthalmic Exam in one eye) can develop.
• Patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship may alter head positioning to compensate.

Diagnosis

There are several historical factors to consider in determining the cause and treatment of strabismus.

History

• Onset:
  • Age at onset
  • History of birth trauma
  • Sudden or gradual onset
• Family history Family History Adult Health Maintenance of strabismus may be a contributing factor.
• Exposure to toxins
• Symptoms: 
  • May have no subjective symptoms
  • Diplopia Diplopia A visual symptom in which a single object is perceived by the visual cortex as two objects rather than one. Disorders associated with this condition include refractive errors; strabismus; oculomotor nerve diseases; trochlear nerve diseases; abducens nerve diseases; and diseases of the brain stem and occipital lobe. Myasthenia Gravis
  • Hyperopia Hyperopia Refractive Errors ( farsightedness Farsightedness Refractive Errors)
  • Difficulty reading
  • Eyestrain
  • Headaches

Physical exam

• In infants, look for: 
  • Closing or covering 1 eye when looking at a near object
  • Closing 1 eye when viewing faraway objects
  • Tilting or turning the head
• Assess visual acuity Visual Acuity Clarity or sharpness of ocular vision or the ability of the eye to see fine details. Visual acuity depends on the functions of retina, neuronal transmission, and the interpretative ability of the brain. Normal visual acuity is expressed as 20/20 indicating that one can see at 20 feet what should normally be seen at that distance. Visual acuity can also be influenced by brightness, color, and contrast. Ophthalmic Exam in children or adults.
• Note clinical features:
  • Strabismus in 1 or alternating between eyes
  • Severity
  • Constant or intermittent
  • Asymmetric red reflex Red Reflex Cataracts in Children

Other diagnostic testing

• Asymmetric corneal light reflex
  • Initial screen for strabismus
  • Hold an object several feet in front of a child’s face with a penlight Penlight Ophthalmic Exam next to it.
  • If ocular alignment is normal, the light reflex is positioned centrally and symmetrically in each eye.
  • With strabismus, the reflection of the corneal light reflex will show ocular misalignment.
• Cover test:
  • Cover 1 of the patient’s eyes.
  • Observe the opposite eye for movement.
• Cover/uncover test:
  • Used to detect latent strabismus
  • Each eye is sequentially covered.
  • Refixation movements are observed in the eye affected with strabismus.
  • Small, barely perceptible phorias are common and not pathologic.
• Neuroimaging Neuroimaging Non-invasive methods of visualizing the central nervous system, especially the brain, by various imaging modalities. Febrile Infant studies are rarely needed, but can be considered in children with:
  • Craniofacial malformations
  • Abnormal neurologic exam
  • Head or orbit trauma

Management

Management

Abnormal eye examination or strabismus noted on testing in a child should be referred to a pediatric ophthalmologist.

• Correction of refractive errors Refractive errors By refraction, the light that enters the eye is focused onto a particular point of the retina. The main refractive components of the eye are the cornea and the lens. When the corneal curvature, the refractive power of the lens, does not match the size of the eye, ametropia or a refractive error occurs. Refractive Errors (e.g., myopia Myopia Refractive Errors, hyperopia Hyperopia Refractive Errors):
  • Glasses
  • Contacts
• Amblyopia management:
  • Penalization therapy:
    • Atropine Atropine An alkaloid, originally from atropa belladonna, but found in other plants, mainly solanaceae. Hyoscyamine is the 3(s)-endo isomer of atropine. Anticholinergic Drugs drops causes pupil Pupil The pupil is the space within the eye that permits light to project onto the retina. Anatomically located in front of the lens, the pupil’s size is controlled by the surrounding iris. The pupil provides insight into the function of the central and autonomic nervous systems. Pupil: Physiology and Abnormalities dilation → blurring the vision Vision Ophthalmic Exam in normal eye
    • Eye with strabismus is forced to receive light signals and transmit them to the brain Brain The part of central nervous system that is contained within the skull (cranium). Arising from the neural tube, the embryonic brain is comprised of three major parts including prosencephalon (the forebrain); mesencephalon (the midbrain); and rhombencephalon (the hindbrain). The developed brain consists of cerebrum; cerebellum; and other structures in the brain stem. Nervous System: Anatomy, Structure, and Classification to improve vision Vision Ophthalmic Exam.
  • Occlusion therapy:
    • Patch Patch Nonpalpable lesion > 1 cm in diameter Generalized and Localized Rashes the normal eye
    • Eye with strabismus is forced to receive light signals and transmit them to the brain Brain The part of central nervous system that is contained within the skull (cranium). Arising from the neural tube, the embryonic brain is comprised of three major parts including prosencephalon (the forebrain); mesencephalon (the midbrain); and rhombencephalon (the hindbrain). The developed brain consists of cerebrum; cerebellum; and other structures in the brain stem. Nervous System: Anatomy, Structure, and Classification.
• Surgery to adjust the extraocular muscles

Complications

• Amblyopia: 
  • Permanently reduced vision Vision Ophthalmic Exam in 1 eye caused by failure of the brain Brain The part of central nervous system that is contained within the skull (cranium). Arising from the neural tube, the embryonic brain is comprised of three major parts including prosencephalon (the forebrain); mesencephalon (the midbrain); and rhombencephalon (the hindbrain). The developed brain consists of cerebrum; cerebellum; and other structures in the brain stem. Nervous System: Anatomy, Structure, and Classification to process visual input
  • Over time, only 1 eye is used for vision Vision Ophthalmic Exam.
• Diplopia Diplopia A visual symptom in which a single object is perceived by the visual cortex as two objects rather than one. Disorders associated with this condition include refractive errors; strabismus; oculomotor nerve diseases; trochlear nerve diseases; abducens nerve diseases; and diseases of the brain stem and occipital lobe. Myasthenia Gravis (with acquired strabismus in children > 9 years of age)
• Secondary contracture of the extraocular muscles
• Adverse psychosocial and vocational consequences

Differential Diagnosis

• Ocular instability of infancy: physiologic intermittent misalignment of the eyes during the first few months of life. This instability occurs because of normal initial weakness of infantile extraocular muscles. Ocular instability of infancy may present either with exotropia or esotropia. Diagnosis is clinical. Management is to reassure the parents. In contrast, eye misalignment that is constant or lasts > 4–6 months is pathologic and warrants further investigation.
• Pseudostrabismus: appearance of misalignment of eyes in infants due to epicanthal skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Skin: Structure and Functions fold. An epicanthal skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Skin: Structure and Functions fold covering the medial sclera Sclera The white, opaque, fibrous, outer tunic of the eyeball, covering it entirely excepting the segment covered anteriorly by the cornea. It is essentially avascular but contains apertures for vessels, lymphatics, and nerves. Eye: Anatomy may make the eye appear deviated; however, corneal light reflex testing showing a light reflection on the corneal center excludes true strabismus. Diagnosis is clinical. Management is to reassure the parents. 
• Internuclear ophthalmoplegia Ophthalmoplegia Paralysis of one or more of the ocular muscles due to disorders of the eye muscles, neuromuscular junction, supporting soft tissue, tendons, or innervation to the muscles. Orbital and Preseptal Cellulitis ( INO INO Internuclear ophthalmoplegia (INO) is an ocular movement disorder that affects the conjugate horizontal gaze, meaning the eyes are incapable of moving in a simultaneous and coordinated manner on the horizontal plane. Internuclear Ophthalmoplegia): inability to adduct the eye during voluntary horizontal gaze Horizontal Gaze Internuclear Ophthalmoplegia. Internuclear ophthalmoplegia Ophthalmoplegia Paralysis of one or more of the ocular muscles due to disorders of the eye muscles, neuromuscular junction, supporting soft tissue, tendons, or innervation to the muscles. Orbital and Preseptal Cellulitis is caused by a lesion of the medial longitudinal fasciculus Medial Longitudinal Fasciculus Internuclear Ophthalmoplegia. Bilateral INO INO Internuclear ophthalmoplegia (INO) is an ocular movement disorder that affects the conjugate horizontal gaze, meaning the eyes are incapable of moving in a simultaneous and coordinated manner on the horizontal plane. Internuclear Ophthalmoplegia is commonly seen in multiple sclerosis Sclerosis A pathological process consisting of hardening or fibrosis of an anatomical structure, often a vessel or a nerve. Wilms Tumor and is a clinical diagnosis. However, investigations involving neuroimaging Neuroimaging Non-invasive methods of visualizing the central nervous system, especially the brain, by various imaging modalities. Febrile Infant, especially MRI, help establish the diagnosis. Management of INO INO Internuclear ophthalmoplegia (INO) is an ocular movement disorder that affects the conjugate horizontal gaze, meaning the eyes are incapable of moving in a simultaneous and coordinated manner on the horizontal plane. Internuclear Ophthalmoplegia varies depending on the cause. Prognosis Prognosis A prediction of the probable outcome of a disease based on a individual’s condition and the usual course of the disease as seen in similar situations. Non-Hodgkin Lymphomas mainly depends on the etiology.
• Opsoclonus-myoclonus syndrome Opsoclonus-myoclonus syndrome A neurological condition that is characterized by uncontrolled rapid irregular movements of the eye (opsoclonus) and the muscle (myoclonus) causing unsteady, trembling gait. It is also known as dancing eyes-dancing feet syndrome and is often associated with neoplasms, viral infections, or autoimmune disorders involving the nervous system. Neuroblastoma: rare ocular motility Motility The motor activity of the gastrointestinal tract. Gastrointestinal Motility disorder characterized by involuntary, repetitive, rapid conjugate eye movements occurring in all directions of gaze. This syndrome is more common in children than in adults and can be idiopathic Idiopathic Dermatomyositis or a paraneoplastic disorder. Opsoclonus-myoclonus syndrome Opsoclonus-myoclonus syndrome A neurological condition that is characterized by uncontrolled rapid irregular movements of the eye (opsoclonus) and the muscle (myoclonus) causing unsteady, trembling gait. It is also known as dancing eyes-dancing feet syndrome and is often associated with neoplasms, viral infections, or autoimmune disorders involving the nervous system. Neuroblastoma presents with other neurologic symptoms, such as ataxia Ataxia Impairment of the ability to perform smoothly coordinated voluntary movements. This condition may affect the limbs, trunk, eyes, pharynx, larynx, and other structures. Ataxia may result from impaired sensory or motor function. Sensory ataxia may result from posterior column injury or peripheral nerve diseases. Motor ataxia may be associated with cerebellar diseases; cerebral cortex diseases; thalamic diseases; basal ganglia diseases; injury to the red nucleus; and other conditions. Ataxia-telangiectasia and movement disorders, and diagnosis includes ruling out neuroblastoma Neuroblastoma Neuroblastoma is a malignancy that arises from the neural crest cell derivatives along the sympathetic chain (neuroblasts) and is most commonly located in the adrenal medulla. The tumor often presents in childhood with a flank mass that crosses the midline. Neuroblastoma as an underlying cause. There is no definitive treatment, but steroids Steroids A group of polycyclic compounds closely related biochemically to terpenes. They include cholesterol, numerous hormones, precursors of certain vitamins, bile acids, alcohols (sterols), and certain natural drugs and poisons. Steroids have a common nucleus, a fused, reduced 17-carbon atom ring system, cyclopentanoperhydrophenanthrene. Most steroids also have two methyl groups and an aliphatic side-chain attached to the nucleus. Benign Liver Tumors and immunologic agents have been used.