Strabismus is a condition in which the two eyes are not consistently aligned so that they do not point at the same target simultaneously. One eye may deviate inward, outward, upward or downward, and the deviation can be constant or intermittent. The condition can occur in childhood or adulthood and can result from abnormalities involving ocular alignment, binocular visual development, refractive error, neurological control, extraocular muscles or combinations of these factors. Common terms include esotropia for inward deviation and exotropia for outward deviation, with hypertropia and hypotropia describing vertical deviations.
Normal binocular vision requires coordinated control of the extraocular muscles and visual systems of both eyes. The brain combines the images from the two eyes to produce a unified perception of the visual scene. In Strabismus, misalignment can cause the images to fall on different retinal locations, producing double vision in some circumstances. Young children can suppress the image from the deviating eye, reducing diplopia but potentially interfering with normal development of binocular vision and contributing to amblyopia.
Childhood Strabismus can be associated with refractive errors, developmental factors, neurological conditions, genetic influences and abnormalities of ocular motor control. Some forms occur because the visual system has difficulty maintaining alignment despite otherwise normal eye structures. Adult-onset strabismus can arise from cranial nerve palsies, thyroid-associated eye disease, trauma, neurological disease, decompensation of a previously controlled deviation or other causes. New adult-onset diplopia therefore warrants assessment because the underlying cause may require investigation.
Symptoms and functional effects depend on age of onset and type of deviation. Children may not report double vision because the brain suppresses one image, whereas adults with acquired misalignment commonly experience diplopia, visual confusion, eye strain or difficulty judging depth. Abnormal head posture can sometimes develop as the person attempts to maintain more useful binocular alignment. The visible appearance of the eyes can also have psychosocial consequences, but the medical significance depends on the underlying ocular and neurological circumstances.
Diagnosis involves measuring ocular alignment at different viewing distances and under different fixation conditions. Clinicians may assess eye movements, binocular function, visual acuity, refractive error and the presence of amblyopia. Tests such as cover testing can reveal latent or manifest deviations, while prism measurements quantify the angle of misalignment. In adults, the pattern and onset can guide evaluation for neurological, muscular, orbital or systemic causes.
Treatment is individualised and may include corrective spectacles, management of refractive error, treatment of amblyopia in children, prism correction, selected injections or surgery on the extraocular muscles. Surgery changes the mechanical alignment of the eyes but does not automatically correct every underlying cause or guarantee normal binocular vision. Some patients require treatment primarily to restore functional alignment and relieve diplopia, while others may require intervention because of developmental visual consequences or significant persistent deviation.
Strabismus is distinct from a temporary inability to focus or from ordinary visual fatigue. It is also not synonymous with amblyopia, although the two conditions can be closely associated in childhood. Amblyopia is reduced visual development in an eye or visual system that cannot be explained simply by a structural abnormality, whereas Strabismus concerns ocular alignment. A person can have strabismus without amblyopia and amblyopia without strabismus.
Early identification of childhood Strabismus is important because the developing visual system has time-sensitive opportunities for establishing binocular function. Untreated persistent misalignment can interfere with visual development in susceptible children. Conversely, not every intermittent deviation requires the same treatment, and management depends on age, magnitude, frequency, control, visual acuity, symptoms and underlying cause. Sudden adult-onset strabismus accompanied by neurological symptoms or new persistent double vision requires prompt medical evaluation.
