What causes crossed eyes (strabismus) in children?

TLDR: Strabismus in children is caused by a complex interaction of factors including uncorrected refractive errors, muscle imbalances, neurological conditions, and genetics, and understanding the cause is essential to choosing the right treatment.

The Mechanics of Eye Alignment

The eyes are moved by six extraocular muscles — three pairs that work in opposition — controlled by three cranial nerves (III, IV, and VI). Precise, coordinated eye alignment requires that these muscles receive accurate signals from brain centers that process visual feedback continuously. The superior colliculus, the brainstem, the cerebellum, and the visual cortex all contribute to the neural control of eye alignment. When any part of this system is disrupted — in the muscles themselves, in the nerves, or in the brain — the result can be strabismus.

Strabismus is not a single condition but a family of related disorders defined by the direction and pattern of misalignment. An eye turning inward is called esotropia. An eye turning outward is exotropia. Upward deviation is hypertropia and downward is hypotropia. The deviation may be constant (present all the time) or intermittent (appearing only under certain conditions like fatigue, illness, or sustained near focus). Each type has its own set of causes and treatment implications.

Refractive Error as a Driver of Esotropia

The most common cause of acquired childhood esotropia (inward eye turning that develops between ages 1 and 4) is uncorrected hyperopia — farsightedness. In a farsighted eye, the natural resting focus is behind the retina, requiring the focusing system (accommodation) to work constantly to produce clear vision. Accommodation and convergence (inward eye turning) are neurologically linked — activating one tends to activate the other. In farsighted children, the excessive accommodative effort required to see clearly at any distance drives an equivalent burst of convergence, which can push one or both eyes inward.

This type is called accommodative esotropia, and the treatment is elegantly simple in many cases: correcting the farsighted prescription with glasses removes the need for excess accommodation, reduces the convergence drive, and can partially or fully straighten the eyes. Glasses for accommodative esotropia must be worn consistently — they are not just for seeing more clearly, they are the active treatment for the eye turn.

Muscle Imbalance and Neurological Factors

Some children are born with a structural imbalance in the extraocular muscles — one muscle may be too tight or too weak relative to its partner, pulling the eye out of alignment from birth. Infantile esotropia, presenting within the first 6 months of life, typically involves a large inward angle not explained by refractive error and is thought to have a neurological rather than purely muscular origin. It often runs in families, suggesting a genetic component to the neural development of the vergence system.

Palsy or weakness of specific cranial nerves produces characteristic patterns of strabismus. A sixth nerve palsy, for example, weakens the lateral rectus muscle and causes an inward deviation of the affected eye that is worse when looking toward the affected side. This can be congenital or acquired, and acquired cases always warrant investigation for an underlying cause such as elevated intracranial pressure, tumor, or vascular event.

Duane syndrome is a congenital condition caused by abnormal development of the sixth cranial nerve, resulting in characteristic limitations of eye movement and sometimes a head turn that the child adopts to maintain single vision. Brown syndrome involves a mechanical restriction of the superior oblique tendon that prevents the eye from turning upward in adductor gaze. These structural and neurological causes are less common than refractive or idiopathic causes but are important to identify through a thorough evaluation.

The Role of Genetics

Family history is a significant risk factor for strabismus. A child with one parent who had a childhood eye turn has approximately a four-fold higher risk of developing strabismus compared to the general population. The genetic contribution is complex — multiple genes appear to be involved, and the same family may show different types of strabismus (esotropia vs. exotropia) across affected members. Certain genetic syndromes, including Down syndrome and cerebral palsy, are associated with much higher rates of strabismus due to effects on neurological development.

Prematurity is another important risk factor. Premature infants have higher rates of strabismus, amblyopia, and refractive error than full-term babies, likely due to the disruption of neurological development that occurs when the infant is born before the visual system has fully matured in utero. Any premature infant should have early ophthalmologic screening.

New-Onset Strabismus: When to Act Quickly

While many forms of childhood strabismus develop gradually and can be managed with scheduled evaluations, new-onset strabismus in a child with previously aligned eyes should always be evaluated urgently. A sudden eye turn can be a sign of a serious underlying condition — increased intracranial pressure (as from a brain tumor or hydrocephalus), nerve palsy from an infectious or inflammatory cause, thyroid eye disease in older children, or a vascular event affecting the brainstem.

Parents who notice a new eye turn appearing acutely — particularly if accompanied by headaches, vomiting, double vision, or any change in the child's neurological status — should seek prompt medical evaluation. Once serious causes are ruled out, the management of the strabismus itself can proceed with appropriate care and optimism.

Ready to Protect Your Child's Vision?

At Lumen Vision, we specialize in pediatric optometry, vision therapy, and myopia control. Our team is passionate about catching vision problems early and giving every child the visual foundation they need to thrive. We proudly serve families across the region with comprehensive, compassionate eye care.

Call us at 701-404-9096, visit us online at www.lumen.vision, or schedule your child's appointment directly at scheduleyourexam.com/v3/index.php/6654.