The Five Senses and Beyond: The Encyclopedia of Perception - Jennifer L. Hellier 2017


Strabismus is the medical term for crossed eyes. This is when a person’s eyes will not look at the same place at the same time, which can cause the person to have double vision. One eye may be turned inward (esotropia), outward (exotropia), upward (hypertropia), or downward (hypotropia) compared to the other eye.

Signs and Symptoms

Strabismus occurs when the six extraocular muscles are weak and have poor motor control or when a person has severe farsightedness. The extraocular muscles are controlled by three cranial nerves: oculomotor (cranial nerve III), trochlear (cranial nerve IV), and abducens (cranial nerve VI). These nerves work together to keep a person’s eyes focused on the same location. Strabismus can cause double vision or diplopia in both eyes (binocular diplopia) as well as uncoordinated eye movements, a loss of vision, and/or a loss of depth perception. This occurs because the extraocular muscles do not align the eyes properly so that convergence cannot occur. For instance, one eye will focus on an object but the other eye is turned inward or outward and will focus on a completely different object. Thus, two different images are sent to the brain, which can be confusing for visual perception. In young children, their brains may learn to ignore the image from the weaker eye—usually the turned eye. If the turned eye is only slightly askew, then both eyes may focus on the same object but the images are focused on different regions of the two retinas.


In general, strabismus is the result of an underlying systemic disease, damage to the cranial nerves serving the eye muscles, or inherited. Some diseases resulting in strabismus include but are not limited to cerebral palsy, Down syndrome, stroke, and trauma to the head. Persons with strabismus may have the same eye always turned in the same direction. This can be present all the time or only occurs when the person is tired or ill. In other cases, some patients’ eyes alternate in turning.

In some cases, a person may have “lazy eye,” or amblyopia, where the eye does not focus well. If amblyopia is untreated, it may cause strabismus. As previously stated, the brain may ignore images from the turned eye, which can cause that eye to never see well. Thus, it is imperative to provide treatment as soon as possible.

Diagnoses and Treatments

A health care provider will determine the severity of the strabismus. The provider will perform a general eye exam that tests a person’s visual acuity and corneal light reflex, and perform a retinal exam. The health care provider may also perform a general physical exam to determine if there is an underlying cause for the strabismus.

Treatments for strabismus depend on the cause of the crossed eyes. The underlying cause must be treated first for best results. Many persons with strabismus are prescribed eyeglasses or contact lenses to correct the farsightedness. Treatment for amblyopia will include a patch to be worn over the strong eye. This will force the weaker eye to work hard and should improve its vision. An optometrist may also prescribe eye exercises (vision therapy), prism lenses (to reduce the amount of light into the eye so that it does not turn as much), and/or eye surgery (for severe cases).

In the majority of cases, strabismus can be corrected if treatment is provided as soon as possible. However, if treatment is delayed, then permanent vision loss in the weak eye can occur. In cases of strabismus caused by amblyopia, patching of the good eye should be done prior to age 11. Otherwise the amblyopia may become a permanent condition.

Jennifer L. Hellier

See also: Amblyopia; Cranial Nerves; Diplopia; Visual Perception

Further Reading

American Association for Pediatric Ophthalmology and Strabismus. (2014). Strabismus. Retrieved from

Blumenfeld, Hal. (2010). Neuroanatomy through clinical cases. Sunderland, MA: Sinauer.

Olitsky, S. E., D. Hug, L. S. Plummer, & M. Stass-Isern. (2011). Disorders of eye movement and alignment. In R. M. Kliegman, R. E. Behrman, H. B. Jenson, & B. F. Stanton (Eds.). Nelson Textbook of Pediatrics, 19th ed. (Chapter 615). Philadelphia, PA: Elsevier Saunders.