Schielen

Schielen, medically known as strabismus, is a condition in which the eyes do not align and point at the same object. The misalignment can be latent (phoria) or manifest (tropia), and can be constant or intermittent. In practical terms, one eye may drift inwards (esotropia), outwards (exotropia), or one eye may be higher or lower than the other (hypertropia or hypotropia).

Causes include imbalances or weakness of the eye muscles, refractive errors (notably uncorrected hyperopia), congenital factors, neurological conditions, or trauma. Genetic predisposition is common, and a family history of strabismus increases risk.

Diagnosis is made by an ophthalmologist or optometrist through a comprehensive eye exam. Tests commonly used include the cover test, the Hirschberg test (light reflex), ocular motility assessment, and, when needed, measurements with prism diopters to quantify the deviation. Amblyopia assessment is important in children.

Treatment depends on type and age. Corrective glasses address refractive error, and occlusion therapy (patching) treats amblyopia. Vision therapy and prism glasses can reduce mild misalignment. Surgery to adjust the eye muscles is considered when non-surgical measures are insufficient, and botulinum toxin injections are an alternative in some cases.

Prognosis is better with early detection and consistent treatment; many patients achieve good alignment and binocular vision, though late treatment increases the risk of persistent misalignment and amblyopia.

Epidemiology: Strabismus affects an estimated 2–3% of children; onset is usually in early childhood and is more common in those with a family history or neurodevelopmental conditions.