Strabismus and Ocular Motility Disorders

Strabismus is misalignment of the eyes, in which the two eyes do not point in the same direction, while ocular motility disorders more broadly involve abnormalities of eye movement. These conditions disturb binocular vision and, in children, can interfere with the normal development of sight, making the eyes turn inward, outward, up, or down.

Definition

Strabismus is a misalignment of the visual axes of the two eyes, and ocular motility disorders are abnormalities in the control or range of eye movement; together they reflect failures of the system that keeps the eyes aligned and moving in coordination.

Scope

This entry covers strabismus and disorders of ocular motility as a group: the loss of normal alignment and coordinated movement of the eyes, the distinction between comitant and incomitant deviations, the developmental consequences in children such as amblyopia and loss of binocular vision, and the neural and mechanical causes of abnormal eye movement. It is educational reference material and not clinical guidance.

Core questions

• How is comitant strabismus, in which the deviation is similar in all directions of gaze, distinguished from incomitant strabismus that varies with gaze?
• How does childhood strabismus relate to amblyopia and the development of binocular vision?
• When does an acquired motility disorder signal a cranial nerve or neurological problem?

Key concepts

• Ocular alignment and the visual axes
• Comitant versus incomitant deviation
• Esotropia, exotropia, hypertropia
• Binocular vision and fusion
• Amblyopia
• Cranial nerve palsies (III, IV, VI)
• Diplopia

Mechanisms

Normal alignment depends on coordinated action of the extraocular muscles under neural control, allowing the two eyes to fuse a single binocular image. Strabismus arises when this balance fails: comitant deviations, common in childhood, show a similar angle of misalignment in all directions of gaze and often reflect disorders of the sensory and motor coordination of binocular vision, whereas incomitant deviations vary with gaze direction and frequently reflect a specific muscle restriction or a palsy of one of the ocular motor nerves (third, fourth, or sixth). In children, persistent misalignment can lead the brain to suppress one image, producing amblyopia and loss of binocular function (von Noorden, 2002).

Clinical relevance

Strabismus and motility disorders matter both for visual development in children and as potential signs of neurological disease in adults, since an acquired ocular motor palsy can reflect a cranial nerve or brainstem problem. Recognizing the pattern of misalignment is part of how clinicians distinguish a developmental from a neurological cause. This entry describes the entities and the evidence around them and is not a basis for individual diagnostic or treatment decisions.

Epidemiology

Strabismus is among the more common eye disorders of childhood, and intermittent exotropia and esotropia are frequent forms in pediatric populations, as reflected in the trial populations of the Pediatric Eye Disease Investigator Group (Cotter, 2014; Mohney, 2015). Acquired motility disorders in adults often follow ocular motor nerve palsies.

Evidence & guidelines

Randomized trials by the Pediatric Eye Disease Investigator Group (Cotter, 2014; Mohney, 2015) provide high-quality evidence on the natural history and management of intermittent exotropia in children. The standard textbook synthesis of binocular vision and strabismus is von Noorden and Campos (2002), which frames the theory and classification of ocular misalignment.

History

The study of strabismus and binocular vision matured over the twentieth century, integrating the optics of alignment, the neurology of eye-movement control, and the developmental neuroscience of amblyopia, synthesized in reference works such as von Noorden's Binocular Vision and Ocular Motility. More recently, multicenter randomized trials by the Pediatric Eye Disease Investigator Group have supplied controlled evidence on common childhood deviations (Cotter, 2014; Mohney, 2015).

Debates

How should common childhood deviations such as intermittent exotropia be managed and when does intervention help?

Trials comparing observation with active treatment for intermittent exotropia have informed but not fully settled questions about which children benefit from early intervention and what the natural history of the condition is, leaving the optimal approach an area of continued study.

Seminal works

• von-noorden-2002
• cotter-2014

Frequently asked questions

What is the difference between comitant and incomitant strabismus?

In comitant strabismus the angle of misalignment is about the same in every direction the eyes look, which is typical of childhood deviations, whereas in incomitant strabismus the misalignment changes with gaze direction, which more often points to a restricted muscle or a palsy of one of the nerves that move the eye.

Why is strabismus in children linked to amblyopia?

When a child's eyes are misaligned, the brain may suppress the image from one eye to avoid double vision, and if this persists during visual development that eye can fail to develop normal sight, a condition called amblyopia; this is why childhood strabismus is closely tied to amblyopia and binocular development.