Strabismus

Strabismus, also known as a squint, is a condition in which the eyes are not aligned and do not look at the same point at the same time. One eye may turn inwards (convergent strabismus or esotropia), outwards (divergent strabismus or exotropia), upwards (hypertropia) or downwards (hypotropia). The deviation may be constant or occur only in certain situations, for example when tired or when looking at objects close up or in the distance.

Strabismus is common in young children, but can also develop later in life. In children, it usually develops in the first few years of life, often before the child is three years old. In adults, strabismus can be caused by neurological disorders, a stroke, eye muscle paralysis, trauma or other causes.

How does strabismus develop?

In normal vision, the eye muscles of both eyes work together so that both eyes look at the same point. The brain combines the images from both eyes into a single three-dimensional image. In strabismus, this coordination is disrupted. The cause may lie in the eye muscles themselves, in the nerves that control the eye muscles, or in the brain, which coordinates eye movements.

In children, the brain can learn to suppress the image from the deviating eye, thereby preventing double vision, but the deviating eye may become lazy (amblyopia). In adults who develop strabismus, however, double vision often does occur because the brain no longer learns so easily to ignore the image from one eye.

Types of strabismus

There are different types of strabismus. In manifest strabismus, the deviation is always visible. In latent strabismus (heterophoria), the eyes are normally aligned, but one eye deviates as soon as the eyes stop working together, for example when you cover one eye. Intermittent strabismus only occurs occasionally, for example when tired or when looking at objects close up or far away.

Strabismus can also be classified according to the direction of the deviation and the age at which it develops. Infantile strabismus develops in the first year of life; accommodative strabismus is associated with long-sightedness and often develops around the age of two or three; and acquired strabismus develops later in life.

Recognition and signs

Strabismus is often visible to the naked eye because one eye is looking in a different direction. In young children, it can sometimes be difficult to assess whether strabismus is present, especially if the deviation is minor or only occurs occasionally. Signs may include: the child squinting one eye in bright light, turning their head to one side to look, or having difficulty with depth perception.

Adults who suddenly develop a squint often experience double vision. This may be accompanied by headaches, tiredness or difficulties with reading and driving. Sudden strabismus in adults is a reason to contact an ophthalmologist promptly, as it may indicate an underlying neurological cause.

Examination and diagnosis

A diagnosis of strabismus is made by an ophthalmologist or orthoptist. The examination involves measuring the alignment of the eyes, testing eye movements and assessing the visual acuity of both eyes. Refractive error is also assessed, as long-sightedness can play a role in certain forms of strabismus.

In children, early detection is important to prevent the affected eye from becoming lazy. In the Netherlands, children are screened for strabismus and a lazy eye at the child health clinic. If there is any doubt or if the screening is positive, the child is referred to an ophthalmologist.

Contact lenses and strabismus

In principle, people with strabismus can wear contact lenses if they have a refractive error that can be corrected with lenses. However, contact lenses do not correct the misalignment of the eyes itself. In some forms of strabismus, such as accommodative strabismus associated with long-sightedness, wearing the correct correction – in the form of spectacles or contact lenses – can improve the alignment of the eyes.

If you have strabismus and are considering contact lenses, please discuss this with your optician, optometrist or ophthalmologist. They can assess whether contact lenses are suitable and what correction you require.

When to see an optician

If you suspect your child has a squint, or if you yourself suddenly experience double vision or notice that your eyes are no longer working together properly, please contact your GP, optician or ophthalmologist. Early detection and support are important, especially in children. In adults with sudden strabismus, a prompt examination is needed to determine the cause.